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Relationship between motor skill impairment and severity in children with Asperger syndrome
Research in Autism Spectrum Disorders 1 (2007) 339–349 http://ees.elsevier.com/RASD/default.asp
Relationship between motor skill impairment and severity in children with Asperger syndrome§ Claudia Hilton a,*, Lyndsay Wente a, Patricia LaVesser b, Max Ito c, Carol Reed c, Georgiana Herzberg c a
Department of Occupational Science & Occupational Therapy, Saint Louis University, St. Louis, MO, United States b Program in Occupational Therapy, Washington University, St. Louis, MO, United States c Occupational Therapy Department, Nova Southeastern University, Fort Lauderdale, FL, United States Received 20 December 2006; accepted 22 December 2006
Abstract This study examined the correlation between severity and motor impairment in children with Asperger syndrome (AS). Children, ages 6–12 with AS (N = 51) and a control group of typical children (N = 56), were assessed using the Social Responsiveness Scale (SRS) and the Movement Assessment Battery For Children (MABC). A bivariate correlational design was used to compare the scores (Spearman rank correlational coefficient). Significant differences were seen between typical, mild to moderate and severe categories of SRS scores, based on the Kruskal–Wallis one-way analysis of variance by ranks ( p < .05). Strong correlations were found between the MABC motor impairment levels and the SRS severity levels. This study adds a clearer understanding of the relationship between motor impairment and severity for children with AS. The degree of correlation indicates that motor skill impairment is a function of severity within AS. # 2007 Elsevier Ltd. All rights reserved. Keywords: Pervasive developmental disorder; Autism spectrum disorder; Manual dexterity; Ball skills; Balance skills
1. Introduction Motor skill impairment has been examined in numerous studies of children with Asperger Syndrome (AS). Delayed motor milestones and motor clumsiness are listed in the International
§ This study was started as part of the dissertation research completed by the first author in the pursuit of her doctor of philosophy degree in occupational therapy. * Corresponding author at: Department of Occupational Science & Occupational Therapy, Saint Louis University, 3437 Caroline St., St. Louis, MO 63104, United States. Tel.: +1 314 977 8582; fax: +1 314 977 5414. E-mail address: [email protected] (C. Hilton).
1750-9467/$ – see front matter # 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.rasd.2006.12.003
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Statistical Classification of Diseases and Related Health Problems, 10th Edition (ICD-10; World Health Organization, 1992) as associated, but not necessarily diagnostic features of AS, while the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, Text Revision (DSM-IV-TR; American Psychiatric Association, 2000) does not include any type of motor problem in the diagnosis. Motor skill impairments have been found in 50–100% of participants in previous studies (Ghazuiddin & Butler, 1998; Ghazuiddin, Butler, Tsai, & Ghazuiddin, 1994; Gillberg, 1998; Green et al., 2002; Klin, Volkmar, Ciccetti, & Rourke, 1995). While occupational and physical therapists frequently address these motor problems in their interventions for children with AS, no study has investigated the relationship between motor impairment and severity with these children. Using a recently developed assessment of autistic impairment severity, the Social Responsiveness Scale (SRS, Constantino & Gruber, 2005), with the widely used Movement Assessment Battery for Children (MABC, Henderson & Sugden, 1992), we sought to examine the relationship between these characteristics of children with AS. 2. Literature review Diagnostic criteria for AS include impaired social interaction; restricted, repetitive, and stereotyped patterns of behavior, interests, and activities; and lack of delay in language or cognitive development. AS is a diagnostic category under the larger group of Pervasive Developmental Disorders (PDD) in the ICD-10 (WHO, 1992) and is known as Asperger’s disorder in the DSM-IV-TR (APA, 2000). The United States Department of Health and Human Services, Centers for Disease Control and Prevention (CDC, 2006), recognizes a prevalence rate for PDD between two and six per 1000 individuals. Epidemiological data for AS are not yet available from the CDC, but a recent study estimated a prevalence of 9.5 per 10,000 children (Chakrabarti & Fombonne, 2005), and a four to one ratio of boys to girls is suggested (Ehlers & Gillberg, 1993). Asperger (1944) noted that each of the four case histories in his original paper, describing children who would later be identified as having Asperger syndrome, had some problem with delayed motor skills or motor incoordination. Wing (1981) described 90% of the 34 cases that she had diagnosed based on Asperger’s descriptions as being ‘‘poor at games involving motor skills, and sometimes the executive problems affect the ability to write or to draw’’ (p. 116). 2.1. Long-term participation and pervasive developmental disorders To understand the importance of the limitations of individuals with PDD, it is helpful to explore the long-term issues from studies examining adult participation. Among five studies of between a to 43 subjects, proportions of individuals who participated in successful adult occupations of living semi-independently or independently, participating in paid work, or attending college was less than 50% (Larsen & Mouridsen, 1997; Mawhood, Howlin, & Rutter, 2000; Rumsey, Rappaport, & Sceery, 1985; Szatmari, Bartolucci, Bremner, Bond, & Rich, 1989; Venter, Lord, & Schopler, 1992). The number of subjects who had married was very low, with the highest number of two in one study (Larsen & Mourisen). In a study of 42 adults with HFA and AS, researchers found that they often have extensive need for help from their families and/or society (Engstro¨m, Ekstro¨m, & Emilsson, 2003). These rather bleak adult outcomes may have some relationship to motor impairment. They also support the importance of early identification and intervention addressing the factors, such as motor impairment, that are related to participation, in order to facilitate more successful adult participation.
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2.2. Motor skills in Asperger syndrome 2.2.1. Prevalence of motor problems Research results vary in regard to prevalence of motor problems in persons with AS. Studies examining motor problems or clumsiness in children with AS reveal rates ranging from 50 to 100% and are usually part of a study comparing them to another diagnostic category (Ghazuiddin & Butler, 1998; Ghazuiddin et al., 1994; Gillberg, 1989; Green et al., 2002; Klin et al., 1995; Manjiviona & Prior, 1995; Miyahara et al., 1997). Gillberg found that 83% of the 23 children between ages 5 and 18 with AS either had low scores on the gross motor component of the Griffiths test or were assessed through clinical observation as being ‘‘clumsy.’’ Ghazuiddin et al. used the Bruininks Oseretsky Test of Motor Proficiency (BOTMP, Bruininks, 1978) to examine children with AS between ages 9 and 19. Comparison of the scores from their study to percentile ranks reveals that 91% of the subjects exhibited two standard deviations below the mean on the overall battery score. Fifty-four percent of the gross motor scores were at least two standard deviations below the norm, as were 45% of the fine motor scores. However, several of the subjects tested were beyond the age of the norms for the motor assessment, limiting the validity of these results. Ghazuiddin and Butler (1998) found that all 12 of their subjects with AS, aged 8–15, demonstrated motor coordination problems on the BOTMP (Bruininks, 1978), but actual scores were not available in the report. Klin et al. (1995) used a collection of fine motor assessments (grooved pegboard, Purdue Pegboard, and finger-tapping test) to evaluate fine motor skills, along with observation to evaluate gross motor skills. All of the 21 subjects demonstrated gross motor impairment and 19 of the 21 had impairment of manual dexterity. This was not surprising, because delayed motor milestones and clumsiness were added as diagnostic criteria in this study. Another research group (Miyahara et al., 1997) reported that 85% of their 26 Japanese subjects between 6 and 15 with AS obtained Movement Assessment Battery for Children (MABC, Henderson & Sugden, 1992) scores at least two standard deviations below the norm. All of the children had impaired manual dexterity, 96% had impairment in ball skills, and 92% had impairment in balance skills. The researchers cautioned interpretation of these results, suggesting that the norms for the assessment should be adjusted for Japanese children, and they do reflect more impairment than most other studies. Manjiviona and Prior (1995) found that 50% of their 12 subjects between ages 7 and 17 scored in the definitely impaired range of overall motor performance (at least two standard deviations below the norm) on the Test of Motor Impairment-Henderson Revision, a predecessor of the MABC. In the subscales, 58% scored as definitely impaired in manual dexterity, and 50% scored as definitely impaired in both ball skills and balance. Green et al. (2002) found that 81% of the 11 children between ages 6 and 10 with AS in their study scored in the definitely impaired range and 100% scored in at least the borderline impaired range, according to the MABC. They found that tasks involving aiming and catching a ball and manual dexterity were the most significantly impaired skills, with balance being less impaired. One explanation for the range in prevalence of motor problems in previous studies (50–100%) is that methodology for evaluating this performance skill is inconsistent. Subject age beyond the normative standards of the motor assessments used and the use of non-standardized assessments have been limitations in some studies (Ghazuiddin et al., 1994; Klin et al., 1995). Including motor delay and clumsiness as one of the criteria for subjects identified as having AS has had an impact on some results (Klin et al., 1995). In addition, the definitions of the levels of impairment are not specified in some studies or are reported in a cursory manner.
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2.2.2. Motor impairment diagnoses and Asperger syndrome The two diagnoses that are most commonly used in the current literature referring to children with motor planning difficulties are Developmental Coordination Disorder (DCD) from the DSM-IV and DSM-IV-TR (APA, 1994, 2000) and Specific Developmental Disorder of Motor Function (SDD-MF) from the ICD-10 (Guiffrida, 2001; WHO, 1992). The DCD definition is much more commonly discussed than SDD-MF, and is consistent with criteria for the clumsy child syndrome initially defined by Gubbay (1985). These criteria include late motor milestones and poor motor performances that interfere significantly with the child’s academic achievement and activities of daily living. This category specifically excludes those children whose motor difficulties are due to a general medical condition, including PDD. The SDD-MF definition is similar to DCD, but is slightly more formalized, requiring an intelligence quotient of at least 70 and performance at least two standard deviations below the mean on a standardized test of motor coordination (Spagna, Cantwell, & Baker, 2000). Although the DCD definition does not specify a cutoff, studies typically label a subject as having DCD with a score of one standard deviation below the mean (Crawford, Wilson, & Dewey, 2001). The exact mechanisms contributing to motor problems in persons with AS continue to be enigmatic to researchers. While motor problems have been frequently seen in research examining children with AS, some researchers have also found a relationship between AS and DCD. In a study of children with DCD, Gillberg and Kadesjo¨ (2003) reported DCD to be strongly associated with attention deficits, AS, and other autism spectrum disorders. A significant positive relationship between the presence of motor control problems and AS was also found in a study of 818 Swedish children, who were repeatedly tested at ages 7, 8, 9, and 10 (Kadesjo¨ & Gillberg, 1999). Children with DCD had more symptoms of AS than children without DCD. Specifically, the children with DCD had an average of 3.2 out of a possible 22 AS symptoms, compared with 0.3 in the group without DCD. 2.2.3. Relationship between motor impairment and severity No prior studies have examined the relationship between motor impairment and severity in children with AS. One study did examine the relationship between sensory processing and a measure of severity. Hilton, Graver, and LaVesser (2007) used the SRS to compare the severity of 36 children with high functioning autism spectrum disorders with their sensory processing quadrant scores, as measured by the Sensory Profile (Dunn, 1999). They found moderate to strong correlations between the SRS scores and the sensory processing quadrant scores, indicating that sensory processing is a function of severity within autism spectrum disorders. 3. Research design and methodology This study used a bivariate correlational research design (Spearman rank correlational coefficient). It examined the relationship between severity levels and motor impairment levels in children between age 6 and 12 in two groups, those diagnosed with AS and a control group. Descriptive statistics were used to describe the motor impairment levels and severity. Research procedures to assure the safety and privacy of the subjects and to prevent unnecessary risk for them were included as part of this study in accordance with Institutional Review Board protocol. One hundred seven children participated in the study, 51 with AS and 56 in the control group, and additional information was provided by at least one parent. A convenience sample of participants was tested at six sites. Data were collected from both the child subject and the parent. Participants were children of ages 6–12 years, who were full-term, had an overall IQ of at least
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70, had no history of cerebral palsy or any other diagnosed major neurological condition, were proficient in using the English language, had no history of hearing problems, and had no hearing or sight problems that were not correctible. Diagnostic categories were based on physician diagnosis per parent report on the Data Form and confirmed by the DSM-IV-TR (APA, 2000). 3.1. Recruitment procedure A voluntary convenience sample of participants was recruited through parent contacts and persons known to the principal investigator. Other recruitment efforts were made at parent support group meetings and through support group computer listserves and newsletters for parents of children with autism spectrum disorders and through parents of children in the subject age group in the various metropolitan areas included in the study. The AS group was recruited and tested first, followed by the control group one year later. Similar characteristics were recruited in the control group participants to avoid variance that could not be controlled. 3.2. Assessment measures 3.2.1. Social Responsiveness Scale The SRS (Constantino & Gruber, 2005) was used to assess autistic impairment on a quantitative scale. T-scores from the SRS were used to categorize behavior into levels of typical, mild to moderate, or severe levels. The SRS is a 65-item questionnaire that examines a child’s ability to engage in emotionally appropriate reciprocal social interactions, which is believed to be the core domain of deficiency in all PDDs (Constantino et al., 2003). It is a parent- and/or teacherreport measure of a child’s social impairments in naturalistic social settings. In addition to a total score, the SRS generates five subscale scores, specified to be used solely for treatment planning and treatment effectiveness. They are social awareness (e.g., knows when he/she is too close to someone or invading someone’s space), social cognition (e.g., concentrates too much on parts of things rather than seeing the ‘whole picture’), social communication (e.g., two-way turn taking, appropriate responses), social motivation (e.g., motivational aspects of social interactionaloofness versus social interest), and autistic mannerisms (e.g., has repetitive, odd behaviors, such as hand flapping or rocking). Each item is rated on a four point scale (0 = never true, 1 = sometimes, 2 = often true, 3 = almost always true). Raw scores are converted to t-scores. Higher scores indicate greater severity of social impairment. Psychometric properties of the SRS have been tested in studies involving over 1900 children age 4–15 years (Constantino & Todd, 2003; Constantino et al., 2003). Three-month test-retest reliability of 0.88 was found. Correlation coefficients comparing the SRS scores and all the algorithm scores for the DSM-IV criterion sets generated by the Autism Diagnostic Interview– Revised (ADI–R) were greater than 0.64. Correlation coefficients between mothers, fathers, and teachers ranged from 0.75 to 0.91. This suggests that the SRS is a valid quantitative measure of autistic traits and/or their severity. 3.2.2. Movement Assessment Battery for Children The MABC (Henderson & Sugden, 1992) was used to examine motor skill impairments. The MABC was developed to assess children aged 4–12 years. It contains two assessment components, a teacher checklist and a norm-referenced performance test, both designed to measure impairment of motor function. The norm-referenced performance test was used for the children with AS in this study and the checklist was used for the children in the control group.
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Components of the performance test include manual dexterity, ball skills, and static and dynamic balance. Scores derived from this assessment include overall impairment levels, representing definite motor impairment, borderline motor impairment, or no motor impairment. Because the focus of the test is exclusively on motor acts, it does not have specific verbal instructions and the examiner can use any strategy that he or she believes will lead to proper understanding of the task demands. Raw scores are converted to scaled scores, which range from 0 to 5, with higher scores representing greater impairment. Overall percentile equivalents can be obtained from scaled scores. Test-retest reliability for the MABC ranged from 0.92 to 0.98 (Croce, Horvat, & McCarthy, 2001). Concurrent validity between the MABC and the BOTMP (Bruininks, 1978) resulted in Pearson r-values from 0.60 to 0.90. The MABC was standardized on 1,234 children with generally representative percentages of gender, region, and ethnic origin for the United States population. The 60-question checklist, used with the control group, identifies whether or not children should be tested with the complete assessment. It includes 60 items for which parents or teachers score by how well the child can perform the item. Categories include five sections: (1) items done while the child is stationary and the environment is stable, (2) items done while the child is moving and the environment is stable, (3) items done while the child is stationary and the environment is changing, (4) items done while the child is moving and the environment is changing, and (5) behavioral problems related to motor difficulties. Results in percentile scores that can be categorized into no impairment (<1 standard deviation below the norm), at risk or borderline (between 1 and <2 standard deviations below the norm), and definitely impaired motor skills (2 or more standard deviations below the norm). 3.3. Data analysis procedures All data were analyzed using SPSS for Windows, version 13.0. Data cleaning and validation were completed prior to data analysis. Scatter plot analyses were undertaken for each set of data to examine for the presence of a linear relationship and for data entry error. Data entry errors were corrected using verification from original data forms. A descriptive analysis of the demographic data was completed on the aggregate of the subjects including the frequencies of gender, age, secondary diagnoses, and place of residence. A Kruskal–Wallis one-way analysis of variance by ranks was used to examine the relationship between the independent variable, severity level, and the dependent variable, motor skills impairment level. Spearman’s rank correlation coefficient analysis was used to examine the correlation between the severity levels and motor impairment levels. 3.4. Sample characteristics Fifty-one children with AS and 56 typically developing children and their parents volunteered to participate in this study. Chi-square analyses revealed no significant differences between gender or age in the AS and control groups. Forty-four of the AS subjects were male (86%) and seven were female (14%), while 45 of the control group (80%) were male and 11 (20%) were female (see Table 1). The mean age of the AS group was 9.52 years and of the control was 9.63. A low percentage of ethnic minorities was represented in the sample. Caucasian subjects were 92% of the AS group and 91% of the control group. Spanish, Hispanic or Latino subjects were 6% of the AS group and 7% of the control group. American Indian or Alaskan subjects were 2% of each group.
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Table 1 Characteristics of subjects (N = 107) Characteristic
AS count
AS percent
Control count
Control percent
x2
Gender Male Female
44 7
86 14
45 11
80.4 19.6
.414
Age category 6–8 years 9–10 years 11–12 years
19 18 14
37 35 28
22 18 16
39.3 32.1 28.6
.942
Secondary conditions for the subjects were identified for 29 (57%) of the AS subjects and 3 (5%) of the control group. Most frequently identified conditions included attention deficit/ hyperactivity disorder (35% of AS, 4% of control), anxiety disorder (10% of AS), learning disability (8% of AS, 2% of control), depression (4% of AS), Tourette syndrome (4% of AS), and epilepsy (2% of AS). Parent respondents reported up to four secondary diagnoses for the subjects with AS and up to two diagnoses in the control group. 4. Results Analysis included examination of means and standard deviations of scores for overall motor skills impairment levels, manual dexterity impairment levels, ball skills impairment levels, and static and dynamic balance impairment levels of the subjects with AS. Overall impairment scores consisted of 65% in the category of definite impairment, 25% with borderline impairment, and the remaining 10% with no impairment. All control group subjects were in the no impairment category. Impairment levels in Table 2 illustrate the more common occurrence of definite manual dexterity impairments in comparison to ball skills impairments or balance skill impairments in the AS subjects. Performance indicating no impairments was seen more often in static and dynamic balance, in comparison to ball skills or manual dexterity. SRS severity levels revealed the 56 control group subjects with typical behavior, 41 of the AS group with severe level of behavior, and 10 of the AS group with mild to moderate levels of impairment. Because the data were categorical, a Kruskal–Wallis one-way analysis of variance by ranks was used to compare means, which revealed a significant difference between SRS severity levels and MABC motor impairment levels. Post hoc analyses (Mann–Whitney U) revealed a significant difference between the motor impairment levels and SRS severity levels between typical and both mild to moderate and severe, but not between mild to moderate and severe (see Table 3). Separate analyses were completed with the outliers removed from the data, but no Table 2 MABC impairment levels for subjects with Asperger syndrome (N = 51) Scale
Definite impairment (%)
Borderline impairment (%)
No impairment (%)
Total Manual dexterity Ball skills Static/dynamic balance
65 82 53 33
25 6 22 16
10 12 25 51
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Table 3 Comparison of MABC motor impairment level and SRS severity level (N = 107)
MABC Motor Impairment Level
SRS severity level
N
Mean rank
x2
d.f.
p
Typical Mild to moderate Severe
56 10 41
77 29.9 28.46
82.38
2
.000
Note: Post hoc analyses (Mann–Whitney U) revealed a significant difference between the MABC motor impairment levels and SRS severity levels between typical and both mild to moderate and severe, but not between mild to moderate and severe. Table 4 Relationship between motor impairment levels and SRS t-scores (N = 107) SRS SRS level Social awareness t-score Social cognition t-score Social communication t-score Social motivation t-score Autistic mannerisms t-score **
MABC overall impairment level .856** .745** .770** .764** .735** .788**
p < .01.
difference in significance resulted from this alteration. The SRS levels increase with severity, while MABC impairment levels decrease with severity, so correlations were expected to be negative. Correlational analyses revealed strong relationships between motor impairment levels and all of the SRS t-scores, including total severity and all of the SRS subscales (see Table 4). 5. Discussion Eighty-nine percent of the subjects with AS scored at least one standard deviation below the norm in overall motor skills. Sixty-five percent scored below the fifth percentile (two standard deviations below the norm) on the MABC, which would qualify them as having the comorbid condition of SDD-MF (Spagna et al., 2000). The motor skill results were generally consistent with other studies of motor skills in children with AS (Ghazuiddin & Butler, 1998; Ghazuiddin et al., 1994; Gillberg, 1989; Green et al., 2002; Klin et al., 1995; Manjiviona & Prior, 1995; Miyahara et al., 1997), although the most common occurrence of manual dexterity impairment is not consistent among studies. The comparison of means results indicated a significant difference between MABC motor impairment levels with the three groups of SRS severity levels, but no significant difference was seen between the SRS mild to moderate and severe levels. It is possible that the smaller number of subjects in the mild to moderate severity group could have represented a skewed portion of the population in this category, which would not represent the true relationship between these groups. All relationships between the MABC impairment levels and SRS severity levels and subscale t-scores were strongly correlated. Within a highly selected sample, as is the sample in this study, a moderate or strong correlation is probably representative of a much higher correlation in the general population. The fact that even subtle variations in the motor impairment within this AS group correlate with subtle variations in severity is important. Many variables differ between
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individuals with AS and controls, but the acid test for whether a variable is truly related to autism spectrum is whether that variable varies as a function of severity within the spectrum. The relationship between the MABC impairment levels and the SRS severity levels indicates that motor impairment is related to severity in AS and has significant importance for understanding the neurobiology of AS. The subjects were a convenience sample, recruited from a limited section of the country, with very little ethnic diversity. Using this type of sample gives no assurance of a non-biased group of participants and does not assure the ability to generalize the results. In addition, because the study relied on diagnostic determinations made by various professionals, consistency was not always seen in the determination of the diagnosis, but the SRS gave assurance of levels of severity, according to quantitative measurement of autistic characteristics. Recruitment of a larger number of subjects with mild to moderate severity for future examination would help to substantiate the lack of differentiation between the motor skill impairment levels of mild to moderately severe and severe subjects. Replication of this study in a larger and more ethnically and geographically diverse population would help to strengthen the results of this study and to examine for ethnic differences in motor impairment. Further expansion of the underlying causes of motor impairment in children with AS and other PDDs would also add an important dimension to what is currently known about motor impairments. Another valuable direction of inquiry would be to examine the relationship between motor skills and participation patterns by these children. This would allow better understanding and interpretation of the findings from this study regarding the relative value of motor skills for actual participation. The impact of various interventions addressing the motor performance with children who have AS would add depth to the understanding of this group. Examination of other factors correlated with the presence or lack of motor impairment could expand our understanding of this complex condition. This study has added a clearer understanding of the relationship between motor impairment and severity for children with AS. The use of a standardized assessment of motor impairment along with a quantitative measure of autistic characteristic severity, with a moderately large group of subjects (in comparison to previous studies) adds clarity to the understanding of motor impairment prevalence among children with AS. By using a test of autistic impairment on a quantitative scale across a wide range of severity, it was possible to examine the relationship between motor impairment and severity. The findings indicate that motor impairment is related to severity in AS and has significant importance for understanding the neurobiology of AS. Acknowledgements The authors are thankful to Kate Graver, Jessica Reinken, Andrea Runzi, Mary Crouch, and Nicolle Drew for their tireless commitment to the completion of the data collection. They would like to thank Betty Schaefer, Cathy Crouch, Valerie Harbolovic; Sonia O’Donnell, Lynda Cordry, Tami Morrissey, Deb Dolan, Barb Eckels, Nancy Vanderweile Milligan, Jackie Kilburn, Lois Ehrhard, Joan Smith, Tina Kreummel, Nancy Buchholz, Lori Thompson, Marla Johnson, and Lou Pruitt for their help in finding subjects and coordinating test sites. They are thankful to Charlotte Royeen, Dean of the College of Health Sciences at Saint Louis University, for funding a portion of this research. They would like to thank Diane Lynn Smith, Heidi Israel, Randy Richter, William Siler, William Hart, and Karen Barney, for their help with problem solving. They would like to thank the many wonderful mothers, fathers, and children who volunteered to participate in the study, many of whom traveled several hours to the test sites. Finally, they are thankful for the
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Klin, A., Volkmar, F., Cicchetti, D., & Rourke, B. (1995). Validity and neuropsychological characterization of Asperger syndrome: Convergence with non-verbal learning disabilities syndrome. Journal of Child Psychology and Psychiatry, 36, 1127–1140. Larsen, F. W., & Mouridsen, S. E. (1997). The outcome in children with childhood autism and Asperger syndrome originally diagnosed as psychotic: A 30-year follow-up study of subjects hospitalized as children. European Child and Adolescent Psychiatry, 6, 181–190. Manjiviona, J., & Prior, M. (1995). Comparison of Asperger syndrome and high-functioning autistic children on a test of motor impairment. Journal of Autism and Developmental Disorders, 25(1), 23–39. Mawhood, L., Howlin, P., & Rutter, M. (2000). Autism and developmental receptive language disorder-a comparative follow-up in early adult life. I. Cognitive and language outcomes. Journal of Child Psychology & Psychiatry & Allied Disciplines, 41(5), 547–559. Miyahara, M., Tsujii, M., Hori, M., Nakanishi, K., Kageyama, H., & Sugiyama, T. (1997). Brief report: Motor incoordination in children with Asperger syndrome and learning disabilities. Journal of Autism and Developmental Disorders, 27(5), 595–603. Rumsey, J. M., Rapoport, J. L., & Sceery, W. R. (1985). Autistic children as adults: Psychiatric, social and behavioural outcomes. Journal of the American Academy of Child Psychiatry, 24, 465–473. Spagna, M., Cantwell, D., & Baker, L. (2000). Motor skills disorder: Developmental coordination disorder. In B. J. Sadock & V. J. Sadock (Eds.), Kaplan & Sadock’s Comprehensive Textbook of Psychiatry (7th ed.). Philadelphia: Lippincott Williams & Wilkins. (chap. 36). Szatmari, P., Bartolucci, G., Bremner, R. S., Bond, S., & Rich, S. (1989). A follow-up study of high functioning autistic children. Journal of Autism and Developmental Disorders, 19, 213–226. Venter, A., Lord, C., & Schopler, E. (1992). A follow-up study of high functioning autistic children. Journal of Child Psychology and Psychiatry, 33, 489–507. Wing, L. (1981). Asperger’s syndrome: A clinical account. Psychological Medicine, 11, 115–129. World Health Organization. (1992). The ICD 10 classification of mental and behavioral disorders: Clinical descriptions and diagnostic guidelines. Geneva, Switzerland: World Health Organization.
Relationship between motor skill impairment and severity in children with Asperger syndrome§ Claudia Hilton a,*, Lyndsay Wente a, Patricia LaVesser b, Max Ito c, Carol Reed c, Georgiana Herzberg c a
Department of Occupational Science & Occupational Therapy, Saint Louis University, St. Louis, MO, United States b Program in Occupational Therapy, Washington University, St. Louis, MO, United States c Occupational Therapy Department, Nova Southeastern University, Fort Lauderdale, FL, United States Received 20 December 2006; accepted 22 December 2006
Abstract This study examined the correlation between severity and motor impairment in children with Asperger syndrome (AS). Children, ages 6–12 with AS (N = 51) and a control group of typical children (N = 56), were assessed using the Social Responsiveness Scale (SRS) and the Movement Assessment Battery For Children (MABC). A bivariate correlational design was used to compare the scores (Spearman rank correlational coefficient). Significant differences were seen between typical, mild to moderate and severe categories of SRS scores, based on the Kruskal–Wallis one-way analysis of variance by ranks ( p < .05). Strong correlations were found between the MABC motor impairment levels and the SRS severity levels. This study adds a clearer understanding of the relationship between motor impairment and severity for children with AS. The degree of correlation indicates that motor skill impairment is a function of severity within AS. # 2007 Elsevier Ltd. All rights reserved. Keywords: Pervasive developmental disorder; Autism spectrum disorder; Manual dexterity; Ball skills; Balance skills
1. Introduction Motor skill impairment has been examined in numerous studies of children with Asperger Syndrome (AS). Delayed motor milestones and motor clumsiness are listed in the International
§ This study was started as part of the dissertation research completed by the first author in the pursuit of her doctor of philosophy degree in occupational therapy. * Corresponding author at: Department of Occupational Science & Occupational Therapy, Saint Louis University, 3437 Caroline St., St. Louis, MO 63104, United States. Tel.: +1 314 977 8582; fax: +1 314 977 5414. E-mail address: [email protected] (C. Hilton).
1750-9467/$ – see front matter # 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.rasd.2006.12.003
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Statistical Classification of Diseases and Related Health Problems, 10th Edition (ICD-10; World Health Organization, 1992) as associated, but not necessarily diagnostic features of AS, while the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, Text Revision (DSM-IV-TR; American Psychiatric Association, 2000) does not include any type of motor problem in the diagnosis. Motor skill impairments have been found in 50–100% of participants in previous studies (Ghazuiddin & Butler, 1998; Ghazuiddin, Butler, Tsai, & Ghazuiddin, 1994; Gillberg, 1998; Green et al., 2002; Klin, Volkmar, Ciccetti, & Rourke, 1995). While occupational and physical therapists frequently address these motor problems in their interventions for children with AS, no study has investigated the relationship between motor impairment and severity with these children. Using a recently developed assessment of autistic impairment severity, the Social Responsiveness Scale (SRS, Constantino & Gruber, 2005), with the widely used Movement Assessment Battery for Children (MABC, Henderson & Sugden, 1992), we sought to examine the relationship between these characteristics of children with AS. 2. Literature review Diagnostic criteria for AS include impaired social interaction; restricted, repetitive, and stereotyped patterns of behavior, interests, and activities; and lack of delay in language or cognitive development. AS is a diagnostic category under the larger group of Pervasive Developmental Disorders (PDD) in the ICD-10 (WHO, 1992) and is known as Asperger’s disorder in the DSM-IV-TR (APA, 2000). The United States Department of Health and Human Services, Centers for Disease Control and Prevention (CDC, 2006), recognizes a prevalence rate for PDD between two and six per 1000 individuals. Epidemiological data for AS are not yet available from the CDC, but a recent study estimated a prevalence of 9.5 per 10,000 children (Chakrabarti & Fombonne, 2005), and a four to one ratio of boys to girls is suggested (Ehlers & Gillberg, 1993). Asperger (1944) noted that each of the four case histories in his original paper, describing children who would later be identified as having Asperger syndrome, had some problem with delayed motor skills or motor incoordination. Wing (1981) described 90% of the 34 cases that she had diagnosed based on Asperger’s descriptions as being ‘‘poor at games involving motor skills, and sometimes the executive problems affect the ability to write or to draw’’ (p. 116). 2.1. Long-term participation and pervasive developmental disorders To understand the importance of the limitations of individuals with PDD, it is helpful to explore the long-term issues from studies examining adult participation. Among five studies of between a to 43 subjects, proportions of individuals who participated in successful adult occupations of living semi-independently or independently, participating in paid work, or attending college was less than 50% (Larsen & Mouridsen, 1997; Mawhood, Howlin, & Rutter, 2000; Rumsey, Rappaport, & Sceery, 1985; Szatmari, Bartolucci, Bremner, Bond, & Rich, 1989; Venter, Lord, & Schopler, 1992). The number of subjects who had married was very low, with the highest number of two in one study (Larsen & Mourisen). In a study of 42 adults with HFA and AS, researchers found that they often have extensive need for help from their families and/or society (Engstro¨m, Ekstro¨m, & Emilsson, 2003). These rather bleak adult outcomes may have some relationship to motor impairment. They also support the importance of early identification and intervention addressing the factors, such as motor impairment, that are related to participation, in order to facilitate more successful adult participation.
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2.2. Motor skills in Asperger syndrome 2.2.1. Prevalence of motor problems Research results vary in regard to prevalence of motor problems in persons with AS. Studies examining motor problems or clumsiness in children with AS reveal rates ranging from 50 to 100% and are usually part of a study comparing them to another diagnostic category (Ghazuiddin & Butler, 1998; Ghazuiddin et al., 1994; Gillberg, 1989; Green et al., 2002; Klin et al., 1995; Manjiviona & Prior, 1995; Miyahara et al., 1997). Gillberg found that 83% of the 23 children between ages 5 and 18 with AS either had low scores on the gross motor component of the Griffiths test or were assessed through clinical observation as being ‘‘clumsy.’’ Ghazuiddin et al. used the Bruininks Oseretsky Test of Motor Proficiency (BOTMP, Bruininks, 1978) to examine children with AS between ages 9 and 19. Comparison of the scores from their study to percentile ranks reveals that 91% of the subjects exhibited two standard deviations below the mean on the overall battery score. Fifty-four percent of the gross motor scores were at least two standard deviations below the norm, as were 45% of the fine motor scores. However, several of the subjects tested were beyond the age of the norms for the motor assessment, limiting the validity of these results. Ghazuiddin and Butler (1998) found that all 12 of their subjects with AS, aged 8–15, demonstrated motor coordination problems on the BOTMP (Bruininks, 1978), but actual scores were not available in the report. Klin et al. (1995) used a collection of fine motor assessments (grooved pegboard, Purdue Pegboard, and finger-tapping test) to evaluate fine motor skills, along with observation to evaluate gross motor skills. All of the 21 subjects demonstrated gross motor impairment and 19 of the 21 had impairment of manual dexterity. This was not surprising, because delayed motor milestones and clumsiness were added as diagnostic criteria in this study. Another research group (Miyahara et al., 1997) reported that 85% of their 26 Japanese subjects between 6 and 15 with AS obtained Movement Assessment Battery for Children (MABC, Henderson & Sugden, 1992) scores at least two standard deviations below the norm. All of the children had impaired manual dexterity, 96% had impairment in ball skills, and 92% had impairment in balance skills. The researchers cautioned interpretation of these results, suggesting that the norms for the assessment should be adjusted for Japanese children, and they do reflect more impairment than most other studies. Manjiviona and Prior (1995) found that 50% of their 12 subjects between ages 7 and 17 scored in the definitely impaired range of overall motor performance (at least two standard deviations below the norm) on the Test of Motor Impairment-Henderson Revision, a predecessor of the MABC. In the subscales, 58% scored as definitely impaired in manual dexterity, and 50% scored as definitely impaired in both ball skills and balance. Green et al. (2002) found that 81% of the 11 children between ages 6 and 10 with AS in their study scored in the definitely impaired range and 100% scored in at least the borderline impaired range, according to the MABC. They found that tasks involving aiming and catching a ball and manual dexterity were the most significantly impaired skills, with balance being less impaired. One explanation for the range in prevalence of motor problems in previous studies (50–100%) is that methodology for evaluating this performance skill is inconsistent. Subject age beyond the normative standards of the motor assessments used and the use of non-standardized assessments have been limitations in some studies (Ghazuiddin et al., 1994; Klin et al., 1995). Including motor delay and clumsiness as one of the criteria for subjects identified as having AS has had an impact on some results (Klin et al., 1995). In addition, the definitions of the levels of impairment are not specified in some studies or are reported in a cursory manner.
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2.2.2. Motor impairment diagnoses and Asperger syndrome The two diagnoses that are most commonly used in the current literature referring to children with motor planning difficulties are Developmental Coordination Disorder (DCD) from the DSM-IV and DSM-IV-TR (APA, 1994, 2000) and Specific Developmental Disorder of Motor Function (SDD-MF) from the ICD-10 (Guiffrida, 2001; WHO, 1992). The DCD definition is much more commonly discussed than SDD-MF, and is consistent with criteria for the clumsy child syndrome initially defined by Gubbay (1985). These criteria include late motor milestones and poor motor performances that interfere significantly with the child’s academic achievement and activities of daily living. This category specifically excludes those children whose motor difficulties are due to a general medical condition, including PDD. The SDD-MF definition is similar to DCD, but is slightly more formalized, requiring an intelligence quotient of at least 70 and performance at least two standard deviations below the mean on a standardized test of motor coordination (Spagna, Cantwell, & Baker, 2000). Although the DCD definition does not specify a cutoff, studies typically label a subject as having DCD with a score of one standard deviation below the mean (Crawford, Wilson, & Dewey, 2001). The exact mechanisms contributing to motor problems in persons with AS continue to be enigmatic to researchers. While motor problems have been frequently seen in research examining children with AS, some researchers have also found a relationship between AS and DCD. In a study of children with DCD, Gillberg and Kadesjo¨ (2003) reported DCD to be strongly associated with attention deficits, AS, and other autism spectrum disorders. A significant positive relationship between the presence of motor control problems and AS was also found in a study of 818 Swedish children, who were repeatedly tested at ages 7, 8, 9, and 10 (Kadesjo¨ & Gillberg, 1999). Children with DCD had more symptoms of AS than children without DCD. Specifically, the children with DCD had an average of 3.2 out of a possible 22 AS symptoms, compared with 0.3 in the group without DCD. 2.2.3. Relationship between motor impairment and severity No prior studies have examined the relationship between motor impairment and severity in children with AS. One study did examine the relationship between sensory processing and a measure of severity. Hilton, Graver, and LaVesser (2007) used the SRS to compare the severity of 36 children with high functioning autism spectrum disorders with their sensory processing quadrant scores, as measured by the Sensory Profile (Dunn, 1999). They found moderate to strong correlations between the SRS scores and the sensory processing quadrant scores, indicating that sensory processing is a function of severity within autism spectrum disorders. 3. Research design and methodology This study used a bivariate correlational research design (Spearman rank correlational coefficient). It examined the relationship between severity levels and motor impairment levels in children between age 6 and 12 in two groups, those diagnosed with AS and a control group. Descriptive statistics were used to describe the motor impairment levels and severity. Research procedures to assure the safety and privacy of the subjects and to prevent unnecessary risk for them were included as part of this study in accordance with Institutional Review Board protocol. One hundred seven children participated in the study, 51 with AS and 56 in the control group, and additional information was provided by at least one parent. A convenience sample of participants was tested at six sites. Data were collected from both the child subject and the parent. Participants were children of ages 6–12 years, who were full-term, had an overall IQ of at least
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70, had no history of cerebral palsy or any other diagnosed major neurological condition, were proficient in using the English language, had no history of hearing problems, and had no hearing or sight problems that were not correctible. Diagnostic categories were based on physician diagnosis per parent report on the Data Form and confirmed by the DSM-IV-TR (APA, 2000). 3.1. Recruitment procedure A voluntary convenience sample of participants was recruited through parent contacts and persons known to the principal investigator. Other recruitment efforts were made at parent support group meetings and through support group computer listserves and newsletters for parents of children with autism spectrum disorders and through parents of children in the subject age group in the various metropolitan areas included in the study. The AS group was recruited and tested first, followed by the control group one year later. Similar characteristics were recruited in the control group participants to avoid variance that could not be controlled. 3.2. Assessment measures 3.2.1. Social Responsiveness Scale The SRS (Constantino & Gruber, 2005) was used to assess autistic impairment on a quantitative scale. T-scores from the SRS were used to categorize behavior into levels of typical, mild to moderate, or severe levels. The SRS is a 65-item questionnaire that examines a child’s ability to engage in emotionally appropriate reciprocal social interactions, which is believed to be the core domain of deficiency in all PDDs (Constantino et al., 2003). It is a parent- and/or teacherreport measure of a child’s social impairments in naturalistic social settings. In addition to a total score, the SRS generates five subscale scores, specified to be used solely for treatment planning and treatment effectiveness. They are social awareness (e.g., knows when he/she is too close to someone or invading someone’s space), social cognition (e.g., concentrates too much on parts of things rather than seeing the ‘whole picture’), social communication (e.g., two-way turn taking, appropriate responses), social motivation (e.g., motivational aspects of social interactionaloofness versus social interest), and autistic mannerisms (e.g., has repetitive, odd behaviors, such as hand flapping or rocking). Each item is rated on a four point scale (0 = never true, 1 = sometimes, 2 = often true, 3 = almost always true). Raw scores are converted to t-scores. Higher scores indicate greater severity of social impairment. Psychometric properties of the SRS have been tested in studies involving over 1900 children age 4–15 years (Constantino & Todd, 2003; Constantino et al., 2003). Three-month test-retest reliability of 0.88 was found. Correlation coefficients comparing the SRS scores and all the algorithm scores for the DSM-IV criterion sets generated by the Autism Diagnostic Interview– Revised (ADI–R) were greater than 0.64. Correlation coefficients between mothers, fathers, and teachers ranged from 0.75 to 0.91. This suggests that the SRS is a valid quantitative measure of autistic traits and/or their severity. 3.2.2. Movement Assessment Battery for Children The MABC (Henderson & Sugden, 1992) was used to examine motor skill impairments. The MABC was developed to assess children aged 4–12 years. It contains two assessment components, a teacher checklist and a norm-referenced performance test, both designed to measure impairment of motor function. The norm-referenced performance test was used for the children with AS in this study and the checklist was used for the children in the control group.
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Components of the performance test include manual dexterity, ball skills, and static and dynamic balance. Scores derived from this assessment include overall impairment levels, representing definite motor impairment, borderline motor impairment, or no motor impairment. Because the focus of the test is exclusively on motor acts, it does not have specific verbal instructions and the examiner can use any strategy that he or she believes will lead to proper understanding of the task demands. Raw scores are converted to scaled scores, which range from 0 to 5, with higher scores representing greater impairment. Overall percentile equivalents can be obtained from scaled scores. Test-retest reliability for the MABC ranged from 0.92 to 0.98 (Croce, Horvat, & McCarthy, 2001). Concurrent validity between the MABC and the BOTMP (Bruininks, 1978) resulted in Pearson r-values from 0.60 to 0.90. The MABC was standardized on 1,234 children with generally representative percentages of gender, region, and ethnic origin for the United States population. The 60-question checklist, used with the control group, identifies whether or not children should be tested with the complete assessment. It includes 60 items for which parents or teachers score by how well the child can perform the item. Categories include five sections: (1) items done while the child is stationary and the environment is stable, (2) items done while the child is moving and the environment is stable, (3) items done while the child is stationary and the environment is changing, (4) items done while the child is moving and the environment is changing, and (5) behavioral problems related to motor difficulties. Results in percentile scores that can be categorized into no impairment (<1 standard deviation below the norm), at risk or borderline (between 1 and <2 standard deviations below the norm), and definitely impaired motor skills (2 or more standard deviations below the norm). 3.3. Data analysis procedures All data were analyzed using SPSS for Windows, version 13.0. Data cleaning and validation were completed prior to data analysis. Scatter plot analyses were undertaken for each set of data to examine for the presence of a linear relationship and for data entry error. Data entry errors were corrected using verification from original data forms. A descriptive analysis of the demographic data was completed on the aggregate of the subjects including the frequencies of gender, age, secondary diagnoses, and place of residence. A Kruskal–Wallis one-way analysis of variance by ranks was used to examine the relationship between the independent variable, severity level, and the dependent variable, motor skills impairment level. Spearman’s rank correlation coefficient analysis was used to examine the correlation between the severity levels and motor impairment levels. 3.4. Sample characteristics Fifty-one children with AS and 56 typically developing children and their parents volunteered to participate in this study. Chi-square analyses revealed no significant differences between gender or age in the AS and control groups. Forty-four of the AS subjects were male (86%) and seven were female (14%), while 45 of the control group (80%) were male and 11 (20%) were female (see Table 1). The mean age of the AS group was 9.52 years and of the control was 9.63. A low percentage of ethnic minorities was represented in the sample. Caucasian subjects were 92% of the AS group and 91% of the control group. Spanish, Hispanic or Latino subjects were 6% of the AS group and 7% of the control group. American Indian or Alaskan subjects were 2% of each group.
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Table 1 Characteristics of subjects (N = 107) Characteristic
AS count
AS percent
Control count
Control percent
x2
Gender Male Female
44 7
86 14
45 11
80.4 19.6
.414
Age category 6–8 years 9–10 years 11–12 years
19 18 14
37 35 28
22 18 16
39.3 32.1 28.6
.942
Secondary conditions for the subjects were identified for 29 (57%) of the AS subjects and 3 (5%) of the control group. Most frequently identified conditions included attention deficit/ hyperactivity disorder (35% of AS, 4% of control), anxiety disorder (10% of AS), learning disability (8% of AS, 2% of control), depression (4% of AS), Tourette syndrome (4% of AS), and epilepsy (2% of AS). Parent respondents reported up to four secondary diagnoses for the subjects with AS and up to two diagnoses in the control group. 4. Results Analysis included examination of means and standard deviations of scores for overall motor skills impairment levels, manual dexterity impairment levels, ball skills impairment levels, and static and dynamic balance impairment levels of the subjects with AS. Overall impairment scores consisted of 65% in the category of definite impairment, 25% with borderline impairment, and the remaining 10% with no impairment. All control group subjects were in the no impairment category. Impairment levels in Table 2 illustrate the more common occurrence of definite manual dexterity impairments in comparison to ball skills impairments or balance skill impairments in the AS subjects. Performance indicating no impairments was seen more often in static and dynamic balance, in comparison to ball skills or manual dexterity. SRS severity levels revealed the 56 control group subjects with typical behavior, 41 of the AS group with severe level of behavior, and 10 of the AS group with mild to moderate levels of impairment. Because the data were categorical, a Kruskal–Wallis one-way analysis of variance by ranks was used to compare means, which revealed a significant difference between SRS severity levels and MABC motor impairment levels. Post hoc analyses (Mann–Whitney U) revealed a significant difference between the motor impairment levels and SRS severity levels between typical and both mild to moderate and severe, but not between mild to moderate and severe (see Table 3). Separate analyses were completed with the outliers removed from the data, but no Table 2 MABC impairment levels for subjects with Asperger syndrome (N = 51) Scale
Definite impairment (%)
Borderline impairment (%)
No impairment (%)
Total Manual dexterity Ball skills Static/dynamic balance
65 82 53 33
25 6 22 16
10 12 25 51
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Table 3 Comparison of MABC motor impairment level and SRS severity level (N = 107)
MABC Motor Impairment Level
SRS severity level
N
Mean rank
x2
d.f.
p
Typical Mild to moderate Severe
56 10 41
77 29.9 28.46
82.38
2
.000
Note: Post hoc analyses (Mann–Whitney U) revealed a significant difference between the MABC motor impairment levels and SRS severity levels between typical and both mild to moderate and severe, but not between mild to moderate and severe. Table 4 Relationship between motor impairment levels and SRS t-scores (N = 107) SRS SRS level Social awareness t-score Social cognition t-score Social communication t-score Social motivation t-score Autistic mannerisms t-score **
MABC overall impairment level .856** .745** .770** .764** .735** .788**
p < .01.
difference in significance resulted from this alteration. The SRS levels increase with severity, while MABC impairment levels decrease with severity, so correlations were expected to be negative. Correlational analyses revealed strong relationships between motor impairment levels and all of the SRS t-scores, including total severity and all of the SRS subscales (see Table 4). 5. Discussion Eighty-nine percent of the subjects with AS scored at least one standard deviation below the norm in overall motor skills. Sixty-five percent scored below the fifth percentile (two standard deviations below the norm) on the MABC, which would qualify them as having the comorbid condition of SDD-MF (Spagna et al., 2000). The motor skill results were generally consistent with other studies of motor skills in children with AS (Ghazuiddin & Butler, 1998; Ghazuiddin et al., 1994; Gillberg, 1989; Green et al., 2002; Klin et al., 1995; Manjiviona & Prior, 1995; Miyahara et al., 1997), although the most common occurrence of manual dexterity impairment is not consistent among studies. The comparison of means results indicated a significant difference between MABC motor impairment levels with the three groups of SRS severity levels, but no significant difference was seen between the SRS mild to moderate and severe levels. It is possible that the smaller number of subjects in the mild to moderate severity group could have represented a skewed portion of the population in this category, which would not represent the true relationship between these groups. All relationships between the MABC impairment levels and SRS severity levels and subscale t-scores were strongly correlated. Within a highly selected sample, as is the sample in this study, a moderate or strong correlation is probably representative of a much higher correlation in the general population. The fact that even subtle variations in the motor impairment within this AS group correlate with subtle variations in severity is important. Many variables differ between
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individuals with AS and controls, but the acid test for whether a variable is truly related to autism spectrum is whether that variable varies as a function of severity within the spectrum. The relationship between the MABC impairment levels and the SRS severity levels indicates that motor impairment is related to severity in AS and has significant importance for understanding the neurobiology of AS. The subjects were a convenience sample, recruited from a limited section of the country, with very little ethnic diversity. Using this type of sample gives no assurance of a non-biased group of participants and does not assure the ability to generalize the results. In addition, because the study relied on diagnostic determinations made by various professionals, consistency was not always seen in the determination of the diagnosis, but the SRS gave assurance of levels of severity, according to quantitative measurement of autistic characteristics. Recruitment of a larger number of subjects with mild to moderate severity for future examination would help to substantiate the lack of differentiation between the motor skill impairment levels of mild to moderately severe and severe subjects. Replication of this study in a larger and more ethnically and geographically diverse population would help to strengthen the results of this study and to examine for ethnic differences in motor impairment. Further expansion of the underlying causes of motor impairment in children with AS and other PDDs would also add an important dimension to what is currently known about motor impairments. Another valuable direction of inquiry would be to examine the relationship between motor skills and participation patterns by these children. This would allow better understanding and interpretation of the findings from this study regarding the relative value of motor skills for actual participation. The impact of various interventions addressing the motor performance with children who have AS would add depth to the understanding of this group. Examination of other factors correlated with the presence or lack of motor impairment could expand our understanding of this complex condition. This study has added a clearer understanding of the relationship between motor impairment and severity for children with AS. The use of a standardized assessment of motor impairment along with a quantitative measure of autistic characteristic severity, with a moderately large group of subjects (in comparison to previous studies) adds clarity to the understanding of motor impairment prevalence among children with AS. By using a test of autistic impairment on a quantitative scale across a wide range of severity, it was possible to examine the relationship between motor impairment and severity. The findings indicate that motor impairment is related to severity in AS and has significant importance for understanding the neurobiology of AS. Acknowledgements The authors are thankful to Kate Graver, Jessica Reinken, Andrea Runzi, Mary Crouch, and Nicolle Drew for their tireless commitment to the completion of the data collection. They would like to thank Betty Schaefer, Cathy Crouch, Valerie Harbolovic; Sonia O’Donnell, Lynda Cordry, Tami Morrissey, Deb Dolan, Barb Eckels, Nancy Vanderweile Milligan, Jackie Kilburn, Lois Ehrhard, Joan Smith, Tina Kreummel, Nancy Buchholz, Lori Thompson, Marla Johnson, and Lou Pruitt for their help in finding subjects and coordinating test sites. They are thankful to Charlotte Royeen, Dean of the College of Health Sciences at Saint Louis University, for funding a portion of this research. They would like to thank Diane Lynn Smith, Heidi Israel, Randy Richter, William Siler, William Hart, and Karen Barney, for their help with problem solving. They would like to thank the many wonderful mothers, fathers, and children who volunteered to participate in the study, many of whom traveled several hours to the test sites. Finally, they are thankful for the
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