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Growth and psychomotor development of patients with Duchenne muscular dystrophy
e u r o p e a n j o u r n a l o f p a e d i a t r i c n e u r o l o g y x x x ( 2 0 1 3 ) 1 e7
Official Journal of the European Paediatric Neurology Society
Original article
Growth and psychomotor development of patients with Duchenne muscular dystrophy Elisabeth Sarrazin a,b,c,*, Maja von der Hagen d, Ulrike Schara e, Katja von Au b, Angela M. Kaindl a,b,c a
Department of Pediatric Neurology, Charite´ e Universita¨tsmedizin Berlin, Campus Virchow-Klinikum, Augustenburger Platz 1, 13353 Berlin, Germany b SPZ Pediatric Neurology, Charite´ e Universita¨tsmedizin Berlin, Campus Virchow-Klinikum, Augustenburger Platz 1, 13353 Berlin, Germany c Institute of Cell and Neurobiology, Charite´ e Universita¨tsmedizin Berlin, Campus Mitte, Charite´platz 1, 10115 Berlin, Germany d Department of Pediatric Neurology, Universita¨tskinderklinik der TU Dresden, Germany e Department of Pediatric Neurology, Universita¨tskinderklinik Essen, Germany
article info
abstract
Article history:
Duchenne muscular dystrophy (DMD) is one of the most common hereditary degenerative
Received 17 March 2013
neuromuscular diseases and caused by mutations in the dystrophin gene. The objective of the
Received in revised form
retrospective study was to describe growth and psychomotor development of patients with
19 July 2013
DMD and to detect a possible genotypeephenotype correlation. Data from 263 patients with
Accepted 19 August 2013
DMD (mean age 7.1 years) treated at the Departments of Pediatric Neurology in three German University Hospitals was assessed with respect to body measurements (length, weight, body
Keywords:
mass index BMI, head circumference OFC), motor and cognitive development as well as ge-
Growth
notype (site of mutation). Anthropometric measures and developmental data were compared
Head circumference
to those of a reference population and deviations were analyzed for their frequency in the
Height
cohort as well as in relation to the genotypes. Corticosteroid therapy was implemented in 29
DMD
from 263 patients. Overall 30% of the patients exhibit a short statue (length < 3rd centile) with
Duchenne
onset early in development at 2e5 years of age, and this is even more prevalent when steroid therapy is applied (45% of patients with steroid therapy). The BMI shows a rightwards shift (68% > 50th centile) and the OFC a leftwards shift (65% < 50th centile, 5% microcephaly). Gross motor development is delayed in a third of the patients (mean age at walking 18.3 months, 30% > 18 months, 8% > 24 months). Almost half of the patients show cognitive impairment (26% learning disability, 17% intellectual disability). Although there is no strict genotypeephenotype correlation, particularly mutations in the distal part of the dystrophin gene are frequently associated with short stature and a high rate of microcephaly as well as cognitive impairment. ª 2013 European Paediatric Neurology Society. Published by Elsevier Ltd. All rights reserved.
* Corresponding author. Department of Pediatric Neurology, Charite´ e Universita¨tsmedizin Berlin, Campus Virchow-Klinikum, Augustenburger Platz 1, 13353 Berlin, Germany. E-mail address: [email protected] (E. Sarrazin). 1090-3798/$ e see front matter ª 2013 European Paediatric Neurology Society. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ejpn.2013.08.008
Please cite this article in press as: Sarrazin E, et al., Growth and psychomotor development of patients with Duchenne muscular dystrophy, European Journal of Paediatric Neurology (2013), http://dx.doi.org/10.1016/j.ejpn.2013.08.008
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1.
e u r o p e a n j o u r n a l o f p a e d i a t r i c n e u r o l o g y x x x ( 2 0 1 3 ) 1 e7
Introduction
Duchenne muscular dystrophy (DMD, MIM#310200) is a wellknown X-linked hereditary neuromuscular disease which affects approximately 1 in 3500 live male births.12 It is characterized by progressive muscle weakness with onset in early childhood and loss of ambulation usually early, by the second decade of life.3 DMD has been associated with intellectual disability with a reduction of the mean intelligence quotient (IQ) by about 1 standard deviation (IQ 80e85) and mental retardation in about a third of all patients.5 Obesity as well as underweight and short stature have also been reported.39,21,29,9 Therapy is currently merely symptomatic. DMD is caused by mutations in one of the largest genes of the human genome with a length of 2.3 million base pairs. The dystrophin gene encodes 7 protein isoforms: 3 full length isoforms (Dp427), which are regulated by different promotors and possess unique first exons, and 4 shorter isoforms (Dp260, Dp140, Dp116 and Dp71), which are derived from internal promotors.28 Lack of dystrophin in muscle cells leads to progressive destabilization of the sarcolemma and deterioration of muscle fibers. Isoforms of dystrophin expressed in the CNS play a role in maturation of synapses and release of neurotransmitters,31 a fact that can explain the CNS involvement in many patients. Especially isoforms Dp140 and Dp71 have been linked to cognitive function, while no clear correlation between genotype and motor function or anthropometric data has been reported.23,14,24,10 The effects of mutations on the phenotype depend mainly on whether or not they disrupt the open translational reading frame, a concept referred to as frame shift hypothesis.25 The latter holds true for over 90% of cases.2 Thereby, in-frame mutations result in partly functional proteins causing the milder phenotype of Becker Muscular Dystrophy (BMD), whereas out-of-frame mutations result in a truncated dysfunctional dystrophin causing DMD. There is a wide range of clinical presentations apart from the muscle phenotype in DMD patients. The objective of this retrospective data analysis was to compare anthropometric measures of DMD patients to those of a reference population and to determine the percentage presenting with psychomotor delay. The genotype was assessed and patients were subdivided according to site of mutation to determine if there is a genotype phenotype correlation and if genotype can be used as a prognostic factor for CNS involvement.
2.
Patients and methods
2.1.
Patients and data acquisition
Medical records of patients with DMD treated in the Departments of Pediatric Neurology at three German University Hospitals in Essen, Berlin, and Dresden from 1975 until 2011 were reviewed. Inclusion criteria were age over 2 years, clinical presentation suggestive of dystrophinopathy, diagnosis of DMD verified by molecular genetic testing and/or muscle biopsy analysis, and data for head circumference present in the records. Thereby, 263 boys with an age range of 2e17 years
(mean 7 years 1.5 months) of largely (>90%) European origin could be included in the study. Anthropometric measurements of the occipito-frontal head circumference (OFC), height, and weight were retrospectively collected from the medical records. Body mass index (BMI) was calculated for each patient. Additional parameters recorded were: anthropometric measurements at birth, genotype, corticosteroid therapy for 6 months or more prior to the follow up visit, age at walking as a milestone in motor development, and data depicting cognitive development. Since information on IQ was available only in a small subset of patients, the cognitive development of patients was categorized according to their schooling (normal school, special school for learning disabilities/mental retardation) in addition to their IQ values assessed through the Kaufman Assessment Battery for Children or Wechsler Intelligence Scale for Children. The number of patients for whom data was present for each variable is given in Supplemental Table 1. Steroid therapy was implemented in 29 of the 263 children at the time of data acquisition, the low percentage of treated boys being largely due to the retrospective nature of the study and in part due to the age of the children. In the steroidtreated cohort, 26 boys were treated with deflazacort 0.9 mg per kg bodyweight, whereas the remaining 3 received prednisolone 0.75 mg per kg bodyweight on a 10 days on and 10 days off scheme. Detailed data on the nutrition was not available in a representative number of DMD patients.
2.2.
Data analysis
Growth percentile (P, percentile, e.g., P3, 3rd centile) was determined for each patient using age and sex matched reference populations: for head circumference and height,34 for BMI,19 and for anthropometric data at birth.36 Genotypes were grouped according to site of mutation and subsequently according to affected isoforms of dystrophin. Motor development was rated, depending on the age when the patient learned to walk independently, as within the normal range (walking up to 18 months), delayed (walking at 18e24 months) and severely delayed (walking after 24 months of age). Patients were further categorized according to their cognitive development as within the normal range, presenting with learning disability, or presenting with intellectual disability. Frequency analyses were performed for distribution of percentiles for growth at birth and at follow up as well as for motor and cognitive development. All parameters were analyzed according to their frequency in the patient cohort and with respect to the genotype. The type of mutation and the frequency of deletions and deletion breakpoints were assessed.
3.
Results
3.1.
Anthropometric measures
Length, weight and OFC were normally distributed at birth (Fig. 1(A)) but became abnormal later in development (Fig. 1(B)). Overall almost 30% of patients with DMD exhibit a
Please cite this article in press as: Sarrazin E, et al., Growth and psychomotor development of patients with Duchenne muscular dystrophy, European Journal of Paediatric Neurology (2013), http://dx.doi.org/10.1016/j.ejpn.2013.08.008
e u r o p e a n j o u r n a l o f p a e d i a t r i c n e u r o l o g y x x x ( 2 0 1 3 ) 1 e7
3
Fig. 1 e Anthropometric data of patients with DMD. Distribution of standardized height, weight and OFC (A) at birth and (B) at follow up (all patients, measurements are given as percentiles). (C) Dotplots depicting anthropometric data in comparison with sex and age matched percentiles.
short stature (length < P3). The slowing of growth occurs early in development, as DMD patients aged 2e5 years are already shorter than their peers and almost 30% of that age group present with short stature (Fig. 1(C)). In children treated with corticosteroids short stature is more prevalent (45% of patients, 13 of 29 DMD patients treated with steroids).
The distribution of BMI shows a rightwards shift with overall 68% of patients having a BMI > P50, while severe underweight presents a problem mainly in older patients (12% < P3 in patients 9e17 years, N ¼ 65, data not shown). Head circumference tends to be smaller than population norms (65% < P50, 5% microcephaly instead of expected 3% in
Please cite this article in press as: Sarrazin E, et al., Growth and psychomotor development of patients with Duchenne muscular dystrophy, European Journal of Paediatric Neurology (2013), http://dx.doi.org/10.1016/j.ejpn.2013.08.008
4
e u r o p e a n j o u r n a l o f p a e d i a t r i c n e u r o l o g y x x x ( 2 0 1 3 ) 1 e7
Please cite this article in press as: Sarrazin E, et al., Growth and psychomotor development of patients with Duchenne muscular dystrophy, European Journal of Paediatric Neurology (2013), http://dx.doi.org/10.1016/j.ejpn.2013.08.008
e u r o p e a n j o u r n a l o f p a e d i a t r i c n e u r o l o g y x x x ( 2 0 1 3 ) 1 e7
normal population) with distribution remaining constant among age groups.
3.2.
with delayed or severely delayed motor developmental milestones.
Motor and cognitive development
4. Data on age at walking without support were available for 193 children. The mean age at walking is 18.3 months. 30% of children with DMD do not walk by 18 months of age, and 8% walked even later than 24 months of age. Data on cognitive development were available for 195 children, almost half of which show cognitive impairment. In our cohort, 57% of patients show normal cognitive development, 26% present with learning difficulties (IQ 85e70), and 17% with intellectual disability (IQ < 70).
3.3.
Genetics
The genetic defect responsible for DMD was identified in 220 of the 263 patients, and DMD diagnosis for the remaining 43 patients was based on muscle biopsy findings. In genetically defined DMD patients, the majority are large intragenic deletions (68%) in the DMD gene, followed by point mutations in 15%, duplications in 12%, and insertions, microdeletions or intronic point mutations in 5%. More than half of the mutations occur in the central region of the gene and thereby affect isoforms Dp427, Dp260, and Dp140 (Fig. 2(A)). Only 10% of mutations occur in the most distal part of the gene, affecting all isoforms of dystrophin. A major deletion hotspot in our cohort lies within exons 45e52 (Fig. 2(B)), with most deletion breakpoints being located in intron 44 and 45 (Fig. 2(C)). These findings are in accordance to data provided in the Leiden database.38
3.4.
5
Discussion
There are significant differences in growth and psychomotor development between DMD patients and sex and age matched controls as well as a range of phenotypes within the cohort that can be predicted to some degree by the genotype. Limitations of the study are due to its retrospective nature.
4.1.
DMD and anthropometric data
Short stature appears to be a feature of DMD with the average height being about 1 standard deviation below the population mean.11,33,39,21,29 While weight and length are normal at birth, slowing of growth occurs within the first few years of development,11 which is congruent with our findings. The etiology of short stature is unclear. Muscular weakness leading to lower bone turnover, growth hormone deficiency as well as chronic inflammatory processes have been proposed as causes but considered unlikely.18,29 As a putative determinant of short stature an affection of the homeobox-containing gene SHOX on chromosome Xp22 has been proposed.29 Our finding illustrating that the percentage of steroid naı¨ve patients exhibiting short stature increases in more distal mutations suggests that another, dystrophin-specific mechanism might play a role. Corticosteroids in DMD therapy are known to aggravate short stature and cause weight gain,27 which was confirmed in our study. In steroid naı¨ve DMD patients, high incidences of obesity in young age and of body weights below the 10th centile in older age have been reported.9
Growth and development by genotype 4.2.
Patients with distal deletions of the DMD gene present more frequently with a small stature, followed by patients with mutations in the central part of the gene (Fig. 2(D)). Of patients with deletions affecting all isoforms of dystrophin, 76% have an OCF below P50 (compared to 65% of the total cohort; Fig. 2(D)), and they show a high, 9.5% rate of microcephaly. There is no apparent influence of the deletion site on the BMI (Fig. 2(D)). Retardation of motor and cognitive development is rare in mutations not affecting isoform Dp140 (Fig. 2E and F). In contrast, loss of Dp140 is associated with cognitive disability, i.e. learning disability or intellectual disability, in 40% of patients compared to 17% in patients lacking Dp427 only and 7% in patients lacking Dp427 and Dp260. Mutations located in the most distal part of the gene (upstream of exon 63) have the most severe effect on development. In this subgroup of patients, the majority of patients presents with developmental abnormalities. 15 of 18 patients with distal mutations display intellectual disability and 15 of 17 present
Motor and cognitive development in DMD patients
Psychomotor delay has been described in patients with DMD, sometimes even as one of the earliest features.13 While the WHO Motor Development Study1 defines a mean age at walking of 12.1 months for healthy individuals (2006), the mean age at walking in our cohort was 18.3 months, in agreement with previous studies which described delayed motor milestones.4,30 Cognitive deficits are a common finding in neuromuscular disorders (for review see Ref. 6), and the association of DMD with non-progressive cognitive dysfunction detected also in our cohort has been widely documented. DMD patients often exhibit a cognitive profile with deficits mainly in the areas of verbal working memory and auditory comprehension, whereas performance IQ is less impaired.16,5 A difference between patients with distal and proximal mutations regarding not only the severity of cognitive impairment, but the specific cognitive profile has been reported recently.7 Neuropsychiatric comorbidity in patients with
Fig. 2 e Genetic defects and anthropometric data of patients with DMD. (A) Mutation frequency within the dystrophin gene is depicted; arrows indicate promotor localization, and protein isoforms are indicated: Dp427, Dp260, Dp140, Dp116, Dp71. (B) Deletion frequency of exons in DMD cohort; (C) location of deletion breakpoints (50 and 30 end); (D) height, BMI, and OFC in percentiles given per genotype; please refer to Supplemental Fig. S1 for respective data excluding corticosteroid-treated DMD patients; (E) motor development by genotype; (F) cognitive development by genotype. Please cite this article in press as: Sarrazin E, et al., Growth and psychomotor development of patients with Duchenne muscular dystrophy, European Journal of Paediatric Neurology (2013), http://dx.doi.org/10.1016/j.ejpn.2013.08.008
6
e u r o p e a n j o u r n a l o f p a e d i a t r i c n e u r o l o g y x x x ( 2 0 1 3 ) 1 e7
DMD could not be assessed retrospectively in our cohort. However, it has been suggested that ADHD (attention deficit hyperactivity disorder), autism, obsessive-compulsive disorders, and social behavioral problems are clinical signs of DMD rather than solely being a reactive response to the chronic illness.17,15 Screening for elevated creatine kinase in boys according to a catalog of clinical criteria including motor milestones and cognition has been proposed.22 In our cohort, 70% of patients are walking at 18 months and 57% exhibit normal cognitive functioning which means that probably the majority would not have been detected by the screening criteria proposed.
4.3.
Genetics
While motor outcome does not depend on genotype,10 intellectual functioning in DMD patients has been associated with isoforms Dp140 and especially Dp71.23,14,24 In our study, we could verify the association of loss of Dp140 and Dp71 and psychomotor delay. Both isoforms are expressed in the developing fetal brain,26 and the Dp71 isoform specifically has been implicated in regulation of glutamatergic synapse organization and function.8 It is hypothesized that the cognitive profile in DMD is a product of the cumulative loss of functional isoforms.35,37 Brain magnetic resonance imaging studies in patients with DMD detected no gross abnormalities in brain structure,32 but with more sensitive analyzing techniques subtle gray matter changes and altered neuronal behavior could be detected.20 However, none of the imaging studies took the genotype into consideration. As to date, there are no studies regarding microcephaly in patients with distal mutations of the DMD gene. Clearly more research is needed to further clarify the mechanisms by which loss of Dp140 and Dp71 alters brain development and enhances the severity of mental retardation in DMD patients.
5.
Conclusion
This large retrospective study combines the analysis of anthropometric data and psychomotor development in DMD patients with genotyping. DMD is associated with the development of short stature and overweight in infancy already prior to corticosteroid therapy and exacerbated through such a treatment. Motor and cognitive development is delayed compared to reference populations in about one third of DMD patients. The site of mutation constitutes an important factor to determine the risk of cognitive impairment. In general, distal mutations, especially ones altering Dp71 expression, are associated with short stature and psychomotor delay. However, the heterogeneity within the DMD population is high and therefore prognoses regarding cognitive phenotype need to be made carefully.
Appendix A. Supplementary data Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.ejpn.2013.08.008.
references
1. WHO Motor Development Study: windows of achievement for six gross motor development milestones. Acta Paediatr Suppl 2006;450:86e95. 2. Aartsma-Rus A, Van Deutekom JC, et al. Entries in the Leiden Duchenne muscular dystrophy mutation database: an overview of mutation types and paradoxical cases that confirm the reading-frame rule. Muscle Nerve 2006;34(2):135e44. 3. Brooke MH, Fenichel GM, et al. Duchenne muscular dystrophy: patterns of clinical progression and effects of supportive therapy. Neurology 1989;39(4):475e81. 4. Bushby KM, Hill A, et al. Failure of early diagnosis in symptomatic Duchenne muscular dystrophy. Lancet 1999;353(9152):557e8. 5. Cotton S, Voudouris NJ, et al. Intelligence and Duchenne muscular dystrophy: full-scale, verbal, and performance intelligence quotients. Dev Med Child Neurol 2001;43(7):497e501. 6. D’Angelo MG, Bresolin N. Cognitive impairment in neuromuscular disorders. Muscle Nerve 2006;34(1):16e33. 7. D’Angelo MG, Lorusso ML, et al. Neurocognitive profiles in Duchenne muscular dystrophy and gene mutation site. Pediatr Neurol 2011;45(5):292e9. 8. Daoud F, Candelario-Martinez A, et al. Role of mental retardation-associated dystrophin-gene product Dp71 in excitatory synapse organization, synaptic plasticity and behavioral functions. PLoS One 2009;4(8):e6574. 9. Davidson ZE, Truby H. A review of nutrition in Duchenne muscular dystrophy. J Hum Nutr Diet 2009;22(5):383e93. 10. Desguerre I, Christov C, et al. Clinical heterogeneity of duchenne muscular dystrophy (DMD): definition of subphenotypes and predictive criteria by long-term follow-up. PLoS One 2009;4(2):e4347. 11. Eiholzer U, Boltshauser E, et al. Short stature: a common feature in Duchenne muscular dystrophy. Eur J Pediatr 1988;147(6):602e5. 12. Emery AE. Population frequencies of inherited neuromuscular diseases e a world survey. Neuromuscul Disord 1991;1(1):19e29. 13. Essex C, Roper H. Lesson of the week: late diagnosis of Duchenne’s muscular dystrophy presenting as global developmental delay. BMJ 2001;323(7303):37e8. 14. Felisari G, Martinelli Boneschi F, et al. Loss of Dp140 dystrophin isoform and intellectual impairment in Duchenne dystrophy. Neurology 2000;55(4):559e64. 15. Hendriksen JG, Vles JS. Neuropsychiatric disorders in males with duchenne muscular dystrophy: frequency rate of attention-deficit hyperactivity disorder (ADHD), autism spectrum disorder, and obsessive-compulsive disorder. J Child Neurol 2008;23(5):477e81. 16. Hinton VJ, De Vivo DC, et al. Poor verbal working memory across intellectual level in boys with Duchenne dystrophy. Neurology 2000;54(11):2127e32. 17. Hinton VJ, Nereo NE, et al. Social behavior problems in boys with Duchenne muscular dystrophy. J Dev Behav Pediatr 2006;27(6):470e6. 18. Kissel JT, Burrow KL, et al. Mononuclear cell analysis of muscle biopsies in prednisone-treated and untreated Duchenne muscular dystrophy. CIDD Study Group. Neurology 1991;41(5):667e72. 19. Kromeyer-Hauschild K, Wabitsch M, et al. Perzentile fu¨r den body-mass-index fu¨r das Kindes-und Jugendalter unter Heranziehung verschiedener deutscher Stichproben. Monatsschr Kinderheilkd 2001;149:807e18. 20. Lv SY, Zou QH, et al. Decreased gray matter concentration and local synchronization of spontaneous activity in the
Please cite this article in press as: Sarrazin E, et al., Growth and psychomotor development of patients with Duchenne muscular dystrophy, European Journal of Paediatric Neurology (2013), http://dx.doi.org/10.1016/j.ejpn.2013.08.008
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30. Parsons EP, Clarke AJ, et al. Developmental progress in Duchenne muscular dystrophy: lessons for earlier detection. Eur J Paediatr Neurol 2004;8(3):145e53. 31. Pilgram GS, Potikanond S, et al. The roles of the dystrophinassociated glycoprotein complex at the synapse. Mol Neurobiol 2010;41(1):1e21. 32. Rae C, Scott RB, et al. Brain biochemistry in Duchenne muscular dystrophy: a 1H magnetic resonance and neuropsychological study. J Neurol Sci 1998;160(2):148e57. 33. Rapaport D, Colletto GM, et al. Short stature in Duchenne muscular dystrophy. Growth Regul 1991;1(1):11e5. 34. Stolzenberg H, Kahl H, et al. Body measurements of children and adolescents in Germany. Results of the German Health Interview and Examination Survey for Children and Adolescents (KiGGS). Bundesgesundheitsblatt Gesundheitsforschung Gesundheitsschutz 2007;50(5e6):659e69. 35. Taylor PJ, Betts GA, et al. Dystrophin gene mutation location and the risk of cognitive impairment in Duchenne muscular dystrophy. PLoS One 2010;5(1):e8803. 36. Voigt M, Fusch C, et al. Analyse des Neugeborenenkollektivs der Bunderepublik Deutschland. Geburtsh Frauenheilk 2006;66(10):956e70. 37. Waite A, Brown SC, et al. The dystrophin-glycoprotein complex in brain development and disease. Trends Neurosci 2012;35(8):487e96. 38. White SJ, den Dunnen JT. Copy number variation in the genome; the human DMD gene as an example. Cytogenet Genome Res 2006;115(3e4):240e6. 39. Willig TN, Carlier L, et al. Nutritional assessment in Duchenne muscular dystrophy. Dev Med Child Neurol 1993;35(12):1074e82.
Please cite this article in press as: Sarrazin E, et al., Growth and psychomotor development of patients with Duchenne muscular dystrophy, European Journal of Paediatric Neurology (2013), http://dx.doi.org/10.1016/j.ejpn.2013.08.008
Official Journal of the European Paediatric Neurology Society
Original article
Growth and psychomotor development of patients with Duchenne muscular dystrophy Elisabeth Sarrazin a,b,c,*, Maja von der Hagen d, Ulrike Schara e, Katja von Au b, Angela M. Kaindl a,b,c a
Department of Pediatric Neurology, Charite´ e Universita¨tsmedizin Berlin, Campus Virchow-Klinikum, Augustenburger Platz 1, 13353 Berlin, Germany b SPZ Pediatric Neurology, Charite´ e Universita¨tsmedizin Berlin, Campus Virchow-Klinikum, Augustenburger Platz 1, 13353 Berlin, Germany c Institute of Cell and Neurobiology, Charite´ e Universita¨tsmedizin Berlin, Campus Mitte, Charite´platz 1, 10115 Berlin, Germany d Department of Pediatric Neurology, Universita¨tskinderklinik der TU Dresden, Germany e Department of Pediatric Neurology, Universita¨tskinderklinik Essen, Germany
article info
abstract
Article history:
Duchenne muscular dystrophy (DMD) is one of the most common hereditary degenerative
Received 17 March 2013
neuromuscular diseases and caused by mutations in the dystrophin gene. The objective of the
Received in revised form
retrospective study was to describe growth and psychomotor development of patients with
19 July 2013
DMD and to detect a possible genotypeephenotype correlation. Data from 263 patients with
Accepted 19 August 2013
DMD (mean age 7.1 years) treated at the Departments of Pediatric Neurology in three German University Hospitals was assessed with respect to body measurements (length, weight, body
Keywords:
mass index BMI, head circumference OFC), motor and cognitive development as well as ge-
Growth
notype (site of mutation). Anthropometric measures and developmental data were compared
Head circumference
to those of a reference population and deviations were analyzed for their frequency in the
Height
cohort as well as in relation to the genotypes. Corticosteroid therapy was implemented in 29
DMD
from 263 patients. Overall 30% of the patients exhibit a short statue (length < 3rd centile) with
Duchenne
onset early in development at 2e5 years of age, and this is even more prevalent when steroid therapy is applied (45% of patients with steroid therapy). The BMI shows a rightwards shift (68% > 50th centile) and the OFC a leftwards shift (65% < 50th centile, 5% microcephaly). Gross motor development is delayed in a third of the patients (mean age at walking 18.3 months, 30% > 18 months, 8% > 24 months). Almost half of the patients show cognitive impairment (26% learning disability, 17% intellectual disability). Although there is no strict genotypeephenotype correlation, particularly mutations in the distal part of the dystrophin gene are frequently associated with short stature and a high rate of microcephaly as well as cognitive impairment. ª 2013 European Paediatric Neurology Society. Published by Elsevier Ltd. All rights reserved.
* Corresponding author. Department of Pediatric Neurology, Charite´ e Universita¨tsmedizin Berlin, Campus Virchow-Klinikum, Augustenburger Platz 1, 13353 Berlin, Germany. E-mail address: [email protected] (E. Sarrazin). 1090-3798/$ e see front matter ª 2013 European Paediatric Neurology Society. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ejpn.2013.08.008
Please cite this article in press as: Sarrazin E, et al., Growth and psychomotor development of patients with Duchenne muscular dystrophy, European Journal of Paediatric Neurology (2013), http://dx.doi.org/10.1016/j.ejpn.2013.08.008
2
1.
e u r o p e a n j o u r n a l o f p a e d i a t r i c n e u r o l o g y x x x ( 2 0 1 3 ) 1 e7
Introduction
Duchenne muscular dystrophy (DMD, MIM#310200) is a wellknown X-linked hereditary neuromuscular disease which affects approximately 1 in 3500 live male births.12 It is characterized by progressive muscle weakness with onset in early childhood and loss of ambulation usually early, by the second decade of life.3 DMD has been associated with intellectual disability with a reduction of the mean intelligence quotient (IQ) by about 1 standard deviation (IQ 80e85) and mental retardation in about a third of all patients.5 Obesity as well as underweight and short stature have also been reported.39,21,29,9 Therapy is currently merely symptomatic. DMD is caused by mutations in one of the largest genes of the human genome with a length of 2.3 million base pairs. The dystrophin gene encodes 7 protein isoforms: 3 full length isoforms (Dp427), which are regulated by different promotors and possess unique first exons, and 4 shorter isoforms (Dp260, Dp140, Dp116 and Dp71), which are derived from internal promotors.28 Lack of dystrophin in muscle cells leads to progressive destabilization of the sarcolemma and deterioration of muscle fibers. Isoforms of dystrophin expressed in the CNS play a role in maturation of synapses and release of neurotransmitters,31 a fact that can explain the CNS involvement in many patients. Especially isoforms Dp140 and Dp71 have been linked to cognitive function, while no clear correlation between genotype and motor function or anthropometric data has been reported.23,14,24,10 The effects of mutations on the phenotype depend mainly on whether or not they disrupt the open translational reading frame, a concept referred to as frame shift hypothesis.25 The latter holds true for over 90% of cases.2 Thereby, in-frame mutations result in partly functional proteins causing the milder phenotype of Becker Muscular Dystrophy (BMD), whereas out-of-frame mutations result in a truncated dysfunctional dystrophin causing DMD. There is a wide range of clinical presentations apart from the muscle phenotype in DMD patients. The objective of this retrospective data analysis was to compare anthropometric measures of DMD patients to those of a reference population and to determine the percentage presenting with psychomotor delay. The genotype was assessed and patients were subdivided according to site of mutation to determine if there is a genotype phenotype correlation and if genotype can be used as a prognostic factor for CNS involvement.
2.
Patients and methods
2.1.
Patients and data acquisition
Medical records of patients with DMD treated in the Departments of Pediatric Neurology at three German University Hospitals in Essen, Berlin, and Dresden from 1975 until 2011 were reviewed. Inclusion criteria were age over 2 years, clinical presentation suggestive of dystrophinopathy, diagnosis of DMD verified by molecular genetic testing and/or muscle biopsy analysis, and data for head circumference present in the records. Thereby, 263 boys with an age range of 2e17 years
(mean 7 years 1.5 months) of largely (>90%) European origin could be included in the study. Anthropometric measurements of the occipito-frontal head circumference (OFC), height, and weight were retrospectively collected from the medical records. Body mass index (BMI) was calculated for each patient. Additional parameters recorded were: anthropometric measurements at birth, genotype, corticosteroid therapy for 6 months or more prior to the follow up visit, age at walking as a milestone in motor development, and data depicting cognitive development. Since information on IQ was available only in a small subset of patients, the cognitive development of patients was categorized according to their schooling (normal school, special school for learning disabilities/mental retardation) in addition to their IQ values assessed through the Kaufman Assessment Battery for Children or Wechsler Intelligence Scale for Children. The number of patients for whom data was present for each variable is given in Supplemental Table 1. Steroid therapy was implemented in 29 of the 263 children at the time of data acquisition, the low percentage of treated boys being largely due to the retrospective nature of the study and in part due to the age of the children. In the steroidtreated cohort, 26 boys were treated with deflazacort 0.9 mg per kg bodyweight, whereas the remaining 3 received prednisolone 0.75 mg per kg bodyweight on a 10 days on and 10 days off scheme. Detailed data on the nutrition was not available in a representative number of DMD patients.
2.2.
Data analysis
Growth percentile (P, percentile, e.g., P3, 3rd centile) was determined for each patient using age and sex matched reference populations: for head circumference and height,34 for BMI,19 and for anthropometric data at birth.36 Genotypes were grouped according to site of mutation and subsequently according to affected isoforms of dystrophin. Motor development was rated, depending on the age when the patient learned to walk independently, as within the normal range (walking up to 18 months), delayed (walking at 18e24 months) and severely delayed (walking after 24 months of age). Patients were further categorized according to their cognitive development as within the normal range, presenting with learning disability, or presenting with intellectual disability. Frequency analyses were performed for distribution of percentiles for growth at birth and at follow up as well as for motor and cognitive development. All parameters were analyzed according to their frequency in the patient cohort and with respect to the genotype. The type of mutation and the frequency of deletions and deletion breakpoints were assessed.
3.
Results
3.1.
Anthropometric measures
Length, weight and OFC were normally distributed at birth (Fig. 1(A)) but became abnormal later in development (Fig. 1(B)). Overall almost 30% of patients with DMD exhibit a
Please cite this article in press as: Sarrazin E, et al., Growth and psychomotor development of patients with Duchenne muscular dystrophy, European Journal of Paediatric Neurology (2013), http://dx.doi.org/10.1016/j.ejpn.2013.08.008
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Fig. 1 e Anthropometric data of patients with DMD. Distribution of standardized height, weight and OFC (A) at birth and (B) at follow up (all patients, measurements are given as percentiles). (C) Dotplots depicting anthropometric data in comparison with sex and age matched percentiles.
short stature (length < P3). The slowing of growth occurs early in development, as DMD patients aged 2e5 years are already shorter than their peers and almost 30% of that age group present with short stature (Fig. 1(C)). In children treated with corticosteroids short stature is more prevalent (45% of patients, 13 of 29 DMD patients treated with steroids).
The distribution of BMI shows a rightwards shift with overall 68% of patients having a BMI > P50, while severe underweight presents a problem mainly in older patients (12% < P3 in patients 9e17 years, N ¼ 65, data not shown). Head circumference tends to be smaller than population norms (65% < P50, 5% microcephaly instead of expected 3% in
Please cite this article in press as: Sarrazin E, et al., Growth and psychomotor development of patients with Duchenne muscular dystrophy, European Journal of Paediatric Neurology (2013), http://dx.doi.org/10.1016/j.ejpn.2013.08.008
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Please cite this article in press as: Sarrazin E, et al., Growth and psychomotor development of patients with Duchenne muscular dystrophy, European Journal of Paediatric Neurology (2013), http://dx.doi.org/10.1016/j.ejpn.2013.08.008
e u r o p e a n j o u r n a l o f p a e d i a t r i c n e u r o l o g y x x x ( 2 0 1 3 ) 1 e7
normal population) with distribution remaining constant among age groups.
3.2.
with delayed or severely delayed motor developmental milestones.
Motor and cognitive development
4. Data on age at walking without support were available for 193 children. The mean age at walking is 18.3 months. 30% of children with DMD do not walk by 18 months of age, and 8% walked even later than 24 months of age. Data on cognitive development were available for 195 children, almost half of which show cognitive impairment. In our cohort, 57% of patients show normal cognitive development, 26% present with learning difficulties (IQ 85e70), and 17% with intellectual disability (IQ < 70).
3.3.
Genetics
The genetic defect responsible for DMD was identified in 220 of the 263 patients, and DMD diagnosis for the remaining 43 patients was based on muscle biopsy findings. In genetically defined DMD patients, the majority are large intragenic deletions (68%) in the DMD gene, followed by point mutations in 15%, duplications in 12%, and insertions, microdeletions or intronic point mutations in 5%. More than half of the mutations occur in the central region of the gene and thereby affect isoforms Dp427, Dp260, and Dp140 (Fig. 2(A)). Only 10% of mutations occur in the most distal part of the gene, affecting all isoforms of dystrophin. A major deletion hotspot in our cohort lies within exons 45e52 (Fig. 2(B)), with most deletion breakpoints being located in intron 44 and 45 (Fig. 2(C)). These findings are in accordance to data provided in the Leiden database.38
3.4.
5
Discussion
There are significant differences in growth and psychomotor development between DMD patients and sex and age matched controls as well as a range of phenotypes within the cohort that can be predicted to some degree by the genotype. Limitations of the study are due to its retrospective nature.
4.1.
DMD and anthropometric data
Short stature appears to be a feature of DMD with the average height being about 1 standard deviation below the population mean.11,33,39,21,29 While weight and length are normal at birth, slowing of growth occurs within the first few years of development,11 which is congruent with our findings. The etiology of short stature is unclear. Muscular weakness leading to lower bone turnover, growth hormone deficiency as well as chronic inflammatory processes have been proposed as causes but considered unlikely.18,29 As a putative determinant of short stature an affection of the homeobox-containing gene SHOX on chromosome Xp22 has been proposed.29 Our finding illustrating that the percentage of steroid naı¨ve patients exhibiting short stature increases in more distal mutations suggests that another, dystrophin-specific mechanism might play a role. Corticosteroids in DMD therapy are known to aggravate short stature and cause weight gain,27 which was confirmed in our study. In steroid naı¨ve DMD patients, high incidences of obesity in young age and of body weights below the 10th centile in older age have been reported.9
Growth and development by genotype 4.2.
Patients with distal deletions of the DMD gene present more frequently with a small stature, followed by patients with mutations in the central part of the gene (Fig. 2(D)). Of patients with deletions affecting all isoforms of dystrophin, 76% have an OCF below P50 (compared to 65% of the total cohort; Fig. 2(D)), and they show a high, 9.5% rate of microcephaly. There is no apparent influence of the deletion site on the BMI (Fig. 2(D)). Retardation of motor and cognitive development is rare in mutations not affecting isoform Dp140 (Fig. 2E and F). In contrast, loss of Dp140 is associated with cognitive disability, i.e. learning disability or intellectual disability, in 40% of patients compared to 17% in patients lacking Dp427 only and 7% in patients lacking Dp427 and Dp260. Mutations located in the most distal part of the gene (upstream of exon 63) have the most severe effect on development. In this subgroup of patients, the majority of patients presents with developmental abnormalities. 15 of 18 patients with distal mutations display intellectual disability and 15 of 17 present
Motor and cognitive development in DMD patients
Psychomotor delay has been described in patients with DMD, sometimes even as one of the earliest features.13 While the WHO Motor Development Study1 defines a mean age at walking of 12.1 months for healthy individuals (2006), the mean age at walking in our cohort was 18.3 months, in agreement with previous studies which described delayed motor milestones.4,30 Cognitive deficits are a common finding in neuromuscular disorders (for review see Ref. 6), and the association of DMD with non-progressive cognitive dysfunction detected also in our cohort has been widely documented. DMD patients often exhibit a cognitive profile with deficits mainly in the areas of verbal working memory and auditory comprehension, whereas performance IQ is less impaired.16,5 A difference between patients with distal and proximal mutations regarding not only the severity of cognitive impairment, but the specific cognitive profile has been reported recently.7 Neuropsychiatric comorbidity in patients with
Fig. 2 e Genetic defects and anthropometric data of patients with DMD. (A) Mutation frequency within the dystrophin gene is depicted; arrows indicate promotor localization, and protein isoforms are indicated: Dp427, Dp260, Dp140, Dp116, Dp71. (B) Deletion frequency of exons in DMD cohort; (C) location of deletion breakpoints (50 and 30 end); (D) height, BMI, and OFC in percentiles given per genotype; please refer to Supplemental Fig. S1 for respective data excluding corticosteroid-treated DMD patients; (E) motor development by genotype; (F) cognitive development by genotype. Please cite this article in press as: Sarrazin E, et al., Growth and psychomotor development of patients with Duchenne muscular dystrophy, European Journal of Paediatric Neurology (2013), http://dx.doi.org/10.1016/j.ejpn.2013.08.008
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DMD could not be assessed retrospectively in our cohort. However, it has been suggested that ADHD (attention deficit hyperactivity disorder), autism, obsessive-compulsive disorders, and social behavioral problems are clinical signs of DMD rather than solely being a reactive response to the chronic illness.17,15 Screening for elevated creatine kinase in boys according to a catalog of clinical criteria including motor milestones and cognition has been proposed.22 In our cohort, 70% of patients are walking at 18 months and 57% exhibit normal cognitive functioning which means that probably the majority would not have been detected by the screening criteria proposed.
4.3.
Genetics
While motor outcome does not depend on genotype,10 intellectual functioning in DMD patients has been associated with isoforms Dp140 and especially Dp71.23,14,24 In our study, we could verify the association of loss of Dp140 and Dp71 and psychomotor delay. Both isoforms are expressed in the developing fetal brain,26 and the Dp71 isoform specifically has been implicated in regulation of glutamatergic synapse organization and function.8 It is hypothesized that the cognitive profile in DMD is a product of the cumulative loss of functional isoforms.35,37 Brain magnetic resonance imaging studies in patients with DMD detected no gross abnormalities in brain structure,32 but with more sensitive analyzing techniques subtle gray matter changes and altered neuronal behavior could be detected.20 However, none of the imaging studies took the genotype into consideration. As to date, there are no studies regarding microcephaly in patients with distal mutations of the DMD gene. Clearly more research is needed to further clarify the mechanisms by which loss of Dp140 and Dp71 alters brain development and enhances the severity of mental retardation in DMD patients.
5.
Conclusion
This large retrospective study combines the analysis of anthropometric data and psychomotor development in DMD patients with genotyping. DMD is associated with the development of short stature and overweight in infancy already prior to corticosteroid therapy and exacerbated through such a treatment. Motor and cognitive development is delayed compared to reference populations in about one third of DMD patients. The site of mutation constitutes an important factor to determine the risk of cognitive impairment. In general, distal mutations, especially ones altering Dp71 expression, are associated with short stature and psychomotor delay. However, the heterogeneity within the DMD population is high and therefore prognoses regarding cognitive phenotype need to be made carefully.
Appendix A. Supplementary data Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.ejpn.2013.08.008.
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Please cite this article in press as: Sarrazin E, et al., Growth and psychomotor development of patients with Duchenne muscular dystrophy, European Journal of Paediatric Neurology (2013), http://dx.doi.org/10.1016/j.ejpn.2013.08.008