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Eye movement and neuropsychological studies in first-degree relatives of schizophrenic patients
Schizophrenia Research 54 (2002) 105 – 110 www.elsevier.com/locate/schres
Eye movement and neuropsychological studies in first-degree relatives of schizophrenic patients Janusz K. Rybakowski a,*, Alina Borkowska b b
a Department of Adult Psychiatry, University of Medical Sciences, ul. Szpitalna 27/33, 60-572 Poznan, Poland Department of Psychiatry, University School of Medical Science, ul. Kurpinskiego 19, 85-096 Bydgoszcz, Poland
Received 1 October 2001; accepted 4 October 2001
Abstract The aim of the study was to compare the results of oculomotor and neuropsychological tests in first-episode schizophrenic patients, in both their parents and matched healthy controls. Eye movement tests included fixation and a smooth pursuit task and neuropsychological tests which comprised the Trail Making Test (TMT) A and B, the Stroop Test A and B, and the Wisconsin Card Sorting Test (WCST). There was a significant difference between the 21 patients and their 33 healthy parents in the results of both the eye movement tests and the TMT and WCST but not in the Stroop test. On the other hand, a significant difference between parents and their matched control subjects was found in both oculomotor tests, in the Stroop B, and in two indices of the WCST (completed categories, CC and percentage of conceptual level responses, %CONC). A correlation was obtained between patients and their fathers in the intensity of smooth pursuit disturbances and two indices of the WCST (CC and %CONC), but not between patients and their mothers. The results obtained confirm those of other studies pointing to the presence of a significant impairment on oculomotor and neuropsychological tests in first-degree nonpsychotic relatives (parents) of schizophrenic patients, which may be used as an endophenotypic markers of genetic predisposition to schizophrenia. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Schizophrenia; Eye movements; Neuropsychology; Family studies; Endophenotype
1. Introduction The identification of vulnerability to schizophrenia is compounded by a wide range of phenotypic variability in this illness. It has been postulated that neurophysiological disturbances such as eye movement dysfunctions (Holzman, 2000) or sensory gating deficit (Freedman et al., 1997) as well as neuropsychological abnormalities such as impaired working memory *
Corresponding author. Tel.: +48-61-8475087; fax: +48-618480392. E-mail address: [email protected] (J.K. Rybakowski).
(Franke et al., 1992) or attentional deficits (Cornblatt and Malhotra, 2001) may serve as endophenotypic markers of genetic predisposition to schizophrenia. This was underscored by the fact that all these abnormalities have been reported to exist in a proportion of apparently healthy relatives of schizophrenic patients. Studying various eye movement disturbances, Crawford et al. (1998) found in relatives of schizophrenic probands with high saccadic distractibility greater eye movement disturbances than in relatives of probands with normal distractibility. In the study of Thaker et al. (1996), smooth pursuit abnormalities in persons with schizotypal and schizoid personality were more intense
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in those with familial occurrence of schizophrenia. Also, by studying relatives of schizophrenic patients, these authors observed more eye movement dysfunctions in relatives with a schizophrenia spectrum personality (Thaker et al., 2000). A similar observation was made by Ross et al. (1998a,b) where antisaccade abnormalities in relatives of schizophrenia were more marked with the familial type of disease and were correlated with disturbances of visuospatial working memory. On the other hand, Lencer et al. (2000) found that saccadic abnormalities may occur in relatives of both sporadic and familial schizophrenic patients. Staal et al. (2000), comparing patients with schizophrenia, their healthy siblings and healthy control subjects, found differences in cognitive functioning in the domains of abstraction, attention, executive functioning, spatial memory, and sensory-motor functioning. The schizophrenic probands were impaired on all these five domains, whereas their healthy siblings showed impairments on executive functioning and partially on sensory-motor functioning. For executive functioning, patients and healthy siblings seemed equally impaired as compared to control subjects. Data obtained by D’Amato et al. (1998) which explored, among others, executive functions by means of the Wisconsin Card Sorting Test (WCST) indicated that compared to controls, the performances of schizophrenic siblings on WCST were significantly impaired but they did not statistically differ from the schizophrenic ones. Faraone et al. (2000) found that relatives from multiplex families with schizophrenia had a higher degree of neuropsychological dysfunctions than patients coming from families with a lesser schizophrenic history. Studies on the first-degree relatives of schizophrenic patients (siblings or parents) make a valuable approach to verify the usefulness of the endophenotypic markers. In conjunction with molecular genetic methods such as candidate gene or genome scan, they may help on identification of specific genetic loci connected with schizophrenia. Here, we report our findings with eye movement and neuropsychological disturbances in first-degree relatives (parents) of schizophrenic patients. The aim of the study was to compare the results of oculomotor and neuropsychological tests as potential endophenotypic markers between firstepisode schizophrenic patients, both their parents as well as sex- and age-matched healthy controls.
2. Method 2.1. Subjects Twenty-one patients with first-episode schizophrenia (12 males and 9 females) including two female siblings aged 18 –33 (mean 22) years and both their parents (20 fathers and 20 mothers) aged 38– 69 (mean 48) years were studied. The duration of illness in schizophrenic patients ranged from 6 to 17 (mean 10) months and their mean education level was 12 years (range 8 –17). In schizophrenic patients, the tests were performed before starting pharmacological treatment, drug-free for at least 10 days: 18 patients were neuroleptic-naive at the time of study. In the group of parents, the mean education level was 13 years (range 8– 18). Seven parents studied (3 males, 4 females) had mental illness. Three subjects (2 males, 1 female) were diagnosed with schizophrenia, one female with unipolar depression with psychotic features, and one male with severe schizotypal personality disorder at the verge of psychotic decompensation. Two female parents had bipolar disorder. Six parents were under active treatment at the time of study and in these subjects, the tests were done on medication. An age- and sex-matched healthy control group for the parents was also included: there were 10 male and 10 female subjects aged 39 –69 (mean 49) years, with education level ranging from 10 to 18 (mean 13) years. 2.2. Eye movement measurements Eye trackings were measured by the infrared reflectometry method, using an Ober II system and Grenoble 96 computer program. Investigated subjects were seated in a darkened room in front of the computer screen with goggles (with infrared detectors) on their eyes, the distance between a 17-in. computer screen and the subject’s eye being 60 cm. The conditions for measurements, with sampling rate of 400 Hz and measurement time of 20 s, during two tasks: (1) point fixation on central position on the computer screen and (2) smooth pursuit at the moving point on Lisajou curves. The reason for choosing the Lisajou curves in Ober II system for the measurement of smooth pursuit movement was that
J.K. Rybakowski, A. Borkowska / Schizophrenia Research 54 (2002) 105–110
these curves have constant mathematical characteristics but unlike regular sinusoidal curve, the subject investigated cannot predict the direction of the moving point. The subjects were instructed to keep their eyes fixed on the point during point fixation task and to observe the moving point during smooth pursuit task. Eye movement data were analyzed with CED Cambridge Spike 2 program, with script for eye movement analysis. The main indices of eye movement disturbances were the frequency (n/s) of saccades (catch-up, back-up, and intrusive saccades) occurring during each task and frequency (n/s) of square wave jerks (SWJ), regardless of their amplitude. The periods of artifacts or eye blinks were detected and not included in the analysis. The intensity of eye movement disturbances during fixation and during smooth pursuit was assessed on a 0– 3 scale. The following assessment criteria were applied: For fixation disturbances: 0 = no disturbances; 1 = minimal disturbances: intrusive saccades frequency: 0.01– 0.03; 2 = moderate disturbances: intrusive saccades frequency: 0.04 –0.07; and/or any SWJ; 3 = severe disturbances: intrusive saccades frequency > 0.07 and/or any SWJ. For smooth pursuit disturbances: 0 = no disturbances; 1 = minimal disturbances: intrusive saccades frequency < 0.005; and/or catchup and back-up saccades frequency < 0.005; no SWJ; 2 = moderate disturbances: intrusive saccades, frequency 0.005 – 0.026; and/or catch-up and back-up saccades frequency 0.003 – 0.05; and/or SWJ frequency < 0.005; 3 = severe disturbances: intrusive saccades frequency 0.026 –0.08; and/or catch-up and back-up saccades frequency 0.06 – 0.13; and SWJ frequency >0.005. 2.3. Neuropsychological assessment 2.3.1. The Trail Making Test (TMT) Part A of the test measures psychomotor speed. The results of part B reflect the ability to shift strategy and assess executive function and visuospatial working memory (Reitan, 1958). 2.3.2. The Stroop Color-Word Interference Test The first part of the test (part A), Reading Color Names in black (RNCb), measures verbal abilities and attention. The subject is asked to read as quickly as possible words (color names) printed with black ink on
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the white card. Second part (part B): Naming the Color of Word —different (NCWd)— measures verbal working memory and executive functions. The subject is asked to name color of each printed word. The color of the printed word is different from the color described by the word (Stroop, 1935). 2.3.3. The Wisconsin Card Sorting Test (WCST) The Wisconsin Card Sorting Test (WCST) is a standard test used to assess working memory and executive functions. The percentage of nonperseverative errors (NPE), the percentage of perseverative errors (PE), the number of correctly completed categories (CC), as well as the percentage of conceptual level responses (%CONC) were analyzed. The computer version of the WCST designed by Heaton et al. (1993) with instructions in Polish, was used in this research.
3. Results 3.1. Eye movement tests The results of oculomotor tests in patients, in their parents, and in control group are shown in Table 1. The values of eye movement tests obtained in healthy parents were placed between patients and the sex-matched control group for both fixation and smooth pursuit performance. There was a significant difference between patients and their 33 healthy parents, and also a significant difference between these parents and their 20 matched control subjects. In spite Table 1 The results of oculomotor tests in patients, in their parents, and in control group
Fixation Smooth pursuit
Patients, N = 21
Healthy parents, N = 33
Ill parents, N=7
Healthy controls, N = 20
1.8 ± 1.0* 2.2 ± 0.9*
1.2 ± 1.0*** 1.5 ± 1.2**
2.1 ± 0.9**** 2.3 ± 0.5
0.2 ± 0.4 0.4 ± 0.6
Difference between patients and healthy parents significant, * p < 0.05. Difference between healthy parents and their age-matched controls significant, ** p < 0.01, *** p < 0.001. Difference between ill and healthy parents significant, **** p < 0.05.
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of low number of ill parents, a significant difference was also observed between ill and healthy parents in fixation test and a trend for difference in smooth pursuit movements ( p = 0.09). In all groups (i.e., patients, their parents, and parents’ control group), no gender difference was found as to the values of oculomotor tests. A correlation was also analyzed between the intensity of eye movement disturbances in patients and those in either their fathers or their mothers, both healthy and ill. A highly significant correlation was obtained between the intensity of smooth pursuit disturbances in patients and in their fathers (Spearman r = 0.61, p = 0.003), and also between fixation disturbances in patients and smooth pursuit disturbances in their fathers (r = 0.46, p < 0.05). The respective correlation coefficients between patients and mothers were not significant (0.01 and 0.23). In the case of smooth pursuit disturbances, the difference between the magnitudes of correlation of father – patient and mother – patient was significant ( p < 0.05, two-tailed test). 3.2. Neuropsychological tests The results of neuropsychological tests in patients, in their parents, and in control group are shown in Table 2. There was a significant difference between patients and their 33 healthy parents in all subtests of TMT and WCST, however, such a difference was not observed in any part of the Stroop test. On the other hand, a significant difference between these parents and their matched control subjects was found only in Stroop B and in two indices of the WCST (CC and %CONC). A significant difference was obtained between healthy and ill parents in all indices, except for the WCST NP and %CONC. In any group, no gender difference was found as to the values of these neuropsychological tests, except for the WCST-CC in patients, with women scoring worse ( p < 0.05). The results of correlation analysis revealed a significant correlation between the degree of performance on WCST-CC and %CONC in patients and in their fathers (r = 0.49, p < 0.05 and r = 0.53, p = 0.01, respectively). The respective correlation coefficients between patients and mothers were not significant (0.10 and 0.02). The difference between father –
Table 2 The results of neuropsychological tests in patients, in their parents and in control group
TMT A TMT B Stroop A Stroop B WCST N-P WCST P WCST CC WCST %CONC
Patients, N = 21
Healthy parents, N = 33
Ill parents, N=7
46 ± 22** 133 ± 57** 30 ± 17 93 ± 29 16 ± 10**
31 ± 8 67± 28 25± 5 80± 35*** 7±5
43 ± 14****** 122 ± 28******* 31 ± 5***** 125 ± 36****** 10 ± 5
19 ± 13* 11 ± 7 18 + 7***** 3.8 ± 2.1* 5.1 ± 1.1**** 3.8 ± 1.1***** 54 ± 27* 69± 13**** 59 ± 13
Healthy controls, N = 20 28 ± 6 56 ± 24 23 + 5 61 ± 12 7±3 8±3 5.9 ± 0.4 80 ± 9
Difference between patients and healthy parents significant, * p < 0.01, ** p < 0.001. Difference between healthy parents and their age-matched controls significant, *** p < 0.01, **** p < 0.001. Difference between ill and healthy parents significant, ***** p < 0.05, ****** p < 0.01, ******* p < 0.001.
patient and mother – patient correlation magnitude was, however, not significant either for CC ( p = 0.2) or for %CONC ( p = 0.1) as analyzed by the two-tailed test.
4. Discussion The main finding of our study was a confirmation of validity for oculomotor and for some neuropsychological indices as possible endophenotypic markers of genetic vulnerability to schizophrenia. In apparently healthy parents of schizophrenic patients, these indices were significantly worse than in their matched controls. The results obtained corroborate those of other studies pointing to the presence of significant impairment on eye movement and neuropsychological tests in nonpsychotic relatives of schizophrenic patients (Crawford et al., 1998; D’Amato et al., 1998; Faraone et al., 2000; Lencer et al., 2000; Ross et al., 1998a,b; Staal et al., 2000; Thaker et al., 1996, 2000). In eye movement tests, the values of both fixation and smooth pursuit performance in schizophrenic parents were significantly different from both patients and healthy controls, however, in their magnitude they were much closer to schizophrenic patients than to
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control subjects. Among neuropsychological tests, the results of the Stroop B test were remarkable in that they significantly discriminated between healthy parents and matched controls but not between healthy parents and schizophrenic patients. However, the lack of difference between schizophrenic patients and their healthy parents might be due to age differences between these two groups. This was further supported by the fact that ill parents scored significantly worse on Stroop B test compared both with their healthy counterparts and with schizophrenic offspring. In ill parents, duration of the illness could also contribute to their poor results on this test. A significant difference between healthy parents and their matched controls obtained in the WCST-CC and the %CONC may suggest that, in addition to Stroop B, the performance on these indices may involve a genetic component associated with predisposition to schizophrenia. Such a feature of the %CONC was further supported as the values on this did not differentiate between parents with or without mental illness. There was a difference between ill and healthy parents on most neuropsychological and neurophysiological tests. The most obvious explanation is that part of the deficit in ill parents may be disease-linked as part of developing the full disease itself. The second possibility is that the ill parents may have a higher genetic liability to schizophrenia than the healthy parents. An unexpected finding of our study was the correlation obtained between the intensity of eye movement disturbances in patients and that in their fathers but not in their mothers. Similarly, the patients – fathers (but not the patients – mothers) correlation was obtained with some WCST indices (CC and %CONC), namely those also shown to be the best discriminators between schizophrenics’ parents and their healthy controls. One interpretation of this finding may be that gender differences in schizophrenia may involve an imprinting phenomenon where some genes influencing behavior may either be repressed or expressed depending on which parent they are inherited from (Reik et al., 2000). Furthermore, a predominance of paternal transmission in schizophrenia was shown in two recent studies. Husted et al. (1998) demonstrated that anticipation in familial schizophrenia was significantly greater with paternal than with maternal transmission. Also, the effect of parental age
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on the risk of schizophrenia was shown for fathers but not for mothers (Malaspina et al., 2001). To date, only one study showed possible mapping of eye movement disturbances to a locus on chromosome 6, using genomic scan for the specific region of 6p21-23 (Arolt et al., 1996). Further testing of possible linkage of eye movement disturbances to specific markers on chromosomes 8, 9, 20, and 22 performed by these authors yielded negative results, although they confirmed their previous findings with chromosome 6 (Arolt et al., 1999). Recently, we found a significant association between the intensity of eye movement disturbances (fixation and smooth pursuit) and the Ser-9-Gly polymorphism of dopamine D3 receptor (DRD3) gene both in schizophrenic patients and healthy subjects, where allele 1 (serine) was connected with worse performance (Rybakowski et al., 2001). An association was also recently reported between the Val-158-Met polymorphism of gene for catechol-O-methyl-transpherase (COMT), an enzyme responsible for dopamine metabolism, and the performance on the Wisconsin Card Sorting test in both schizophrenic patients and healthy control subjects, with allele 1 (valine) determining the lower score (Egan et al., 2001). The results of molecular genetic studies applied to such endophenotypes as eye movement and neuropsychological performance suggest that the genetic component for predisposition to schizophrenia may involve an altered dopaminergic activity in prefrontal cortex. This is where both DRD3 receptors and COMT activity are located and also the region mostly connected with the pathophysiology of both oculomotor and neuropsychological tests used in our study. Such a notion was also corroborated by the neuroimaging study of eye movement disturbances in relatives of schizophrenic patients performed recently by O’Driscoll et al. (1999). In schizophrenics’ first-degree relatives exhibiting eye movement disturbances, the features of subtle frontal dysfunction were found and were proposed by these authors as a biological substrate of the genetic predisposition to schizophrenia.
Acknowledgements This work was supported by Polish Committee of Scientific Research (KBN) Grant No. 4P05B 06512.
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References Arolt, V., Lencer, R., Nolte, A., Muller-Myhsok, B., Purmann, S., Schurmann, M., Leutelt, J., Pinnow, M., Schwinger, E., 1996. Eye tracking dysfunction is a putative phenotypic susceptibility marker of schizophrenia and maps to a locus on chromosome 6p in families with multiple occurrence of the disease. Am. J. Med. Genet. 67, 564 – 579. Arolt, V., Lencer, R., Purmann, S., Schu¨rmann, M., Mu¨ller-Myhsok, B., Krecker, K., Schwinger, E., 1999. Testing for linkage of eye tracking dysfunction and schizophrenia to markers on chromosomes 6, 8, 9, 20, and 22 in families multiply affected with schizophrenia. Am. J. Med. Genet. 88, 603 – 606. Cornblatt, B.A., Malhotra, A.K., 2001. Impaired attention as an endophenotype for molecular genetic studies of schizophrenia. Am. J. Med. Genet. 105, 11 – 15. Crawford, T.J., Sharma, T., Puri, B.K., Murray, R.M., Berridge, D.M., Lewis, S.W., 1998. Saccadic eye movements in families multiply affected with schizophrenia: the Maudsley family study. Am. J. Psychiatry 155, 1703 – 1710. D’Amato, T., Saoud, M., Triboulet, P., Bertaud, J.P., Dalery, J., 1998. Vulnerability to schizophrenia I: Familial nature of neuropsychologic indicators. Encephale 24, 442 – 448 (in French). Egan, M.F., Goldberg, T.E., Kolachana, B.S., Callicott, J.H., Mazzanti, C.M., Straub, R.E., Goldman, D., Weinberger, D.R., 2001. Effect of COMT Val108/158 Met phenotype on frontal lobe function and risk for schizophrenia. Proc. Natl. Acad. Sci. U. S. A. 98, 6917 – 6922. Faraone, S.V., Seidman, L.J., Kremen, W.S., Toomey, R., Pepple, J.R., Tsuang, M.T., 2000. Neuropsychologic functioning among the nonpsychotic relatives of schizophrenic patients: the effect of genetic loading. Biol. Psychiatry 48, 120 – 126. Franke, P., Maier, W., Hain, C., Klingler, T., 1992. Wisconsin Card Sorting Test: an indicator of vulnerability to schizophrenia? Schizophr. Res. 6, 243 – 249. Freedman, R., Coon, H., Myles-Worshley, M., Orr-Utreger, A., Olincy, A., Davis, A., Polymeropoulos, M., Holik, J., Hopkins, J., Hoff, M., Rosenthal, J., Waldo, M.C., Reimherr, F., Wender, P., Yaw, J., Young, D.A., Breese, C.R., Adams, C., Patterson, D., Adler, L.E., Kruglyak, L., Leonard, S., Byerley, W., 1997. Linkage of a neuropsychological deficit in schizophrenia to a chromosome 15 locus. Proc. Natl. Acad. Sci. U. S. A. 94, 587 – 592. Heaton, R.K., Chelune, G.J., Talley, J.L., Kay, G.G., Curtis, G.1993. Wisconsin Card Sorting Test Manual. Psychological Assessment Resources, Odessa, FL. Holzman, P.S., 2000. Eye movements and the search for the essence of schizophrenia. Brain Res. Rev. 31, 350 – 356.
Husted, J., Scutt, L.E., Bassett, A.S., 1998. Paternal transmission and anticipation in schizophrenia. Am. J. Med. Genet. 28, 156 – 162. Lencer, R., Malchow, C.P., Trillenberg-Krecker, K.T., Schwinger, E., Arolt, V., 2000. Eye tracking dysfunction (ETD) in families with sporadic and familial schizophrenia. Biol. Psychiatry 47, 391 – 401. Malaspina, D., Harlap, S., Fennig, S., Heiman, D., Nahon, D., Feldman, D., Susser, E.S., 2001. Advancing paternal age and risk of schizophrenia. Arch. Gen. Psychiatry 58, 361 – 367. O’Driscoll, G., Benkelfat, H., Florencio, P.S., Wolff, A.L., Joober, R., Lal, S., Evans, A.C., 1999. Neural correlates of eye tracking deficits in first-degree relatives of schizophrenic patients. Arch. Gen. Psychiatry 56, 1127 – 1134. Reik, W., Wilkinson, L.S., Walter, J., Dean, W., Constancia, M., Maher, E., Feil, R., Kelsey, G., 2000. Imprinting in development and disease: effect of growth and behaviour. Am. J. Med. Genet. 96, 455. Reitan, R.M., 1958. The relation of the trail making test to organic brain damage. J. Cons. Psychol. 19, 393 – 394. Ross, R.G., Olincy, A., Harris, J.G., Radant, A., Adler, L.E., Freedman, R., 1998a. Anticipatory saccades during smooth pursuit eye movements and familial transmission of schizophrenia. Biol. Psychiatry 44, 690 – 697. Ross, R., Harris, J.G., Olincy, A., Radant, A., Adler, L.E., Freedman, R., 1998b. Familial transmission of two independent saccadic abnormalities in schizophrenia. Schizophr. Res. 30, 59 – 70. Rybakowski, J.K., Borkowska, A., Czerski, P.M., Hauser, J., 2001. Dopamine D3 receptor (DRD3) gene polymorphism is associated with the intensity of eye movement disturbances in schizophrenic patients and healthy subjects. Mol. Psychiatry 6, 718 – 724. Staal, W.G., Hijman, R., Hulshoff Pol, H.E., Kahn, R.S., 2000. Neuropsychological dysfunctions in siblings discordant for schizophrenia. Psychiatry Res. 95, 227 – 235. Stroop, J.R., 1935. Studies of interference in serial verbal reactions. J. Exp. Psychol. 18, 643 – 661. Thaker, G.K., Cassady, S.L., Adami, H.M., Moran, M., Ross, D.E., 1996. Eye movements in spectrum personality disorders: comparison of community subjects and relatives of schizophrenic patients. Am. J. Psychiatry 153, 362 – 368. Thaker, G.K., Ross, D.E., Cassady, S.L., Adami, H.M., Medoff, D.R., Sherr, J., 2000. Saccadic eye movement abnormalities in relatives of patients with schizophrenia. Schizophr. Res. 45, 235 – 244.
Eye movement and neuropsychological studies in first-degree relatives of schizophrenic patients Janusz K. Rybakowski a,*, Alina Borkowska b b
a Department of Adult Psychiatry, University of Medical Sciences, ul. Szpitalna 27/33, 60-572 Poznan, Poland Department of Psychiatry, University School of Medical Science, ul. Kurpinskiego 19, 85-096 Bydgoszcz, Poland
Received 1 October 2001; accepted 4 October 2001
Abstract The aim of the study was to compare the results of oculomotor and neuropsychological tests in first-episode schizophrenic patients, in both their parents and matched healthy controls. Eye movement tests included fixation and a smooth pursuit task and neuropsychological tests which comprised the Trail Making Test (TMT) A and B, the Stroop Test A and B, and the Wisconsin Card Sorting Test (WCST). There was a significant difference between the 21 patients and their 33 healthy parents in the results of both the eye movement tests and the TMT and WCST but not in the Stroop test. On the other hand, a significant difference between parents and their matched control subjects was found in both oculomotor tests, in the Stroop B, and in two indices of the WCST (completed categories, CC and percentage of conceptual level responses, %CONC). A correlation was obtained between patients and their fathers in the intensity of smooth pursuit disturbances and two indices of the WCST (CC and %CONC), but not between patients and their mothers. The results obtained confirm those of other studies pointing to the presence of a significant impairment on oculomotor and neuropsychological tests in first-degree nonpsychotic relatives (parents) of schizophrenic patients, which may be used as an endophenotypic markers of genetic predisposition to schizophrenia. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Schizophrenia; Eye movements; Neuropsychology; Family studies; Endophenotype
1. Introduction The identification of vulnerability to schizophrenia is compounded by a wide range of phenotypic variability in this illness. It has been postulated that neurophysiological disturbances such as eye movement dysfunctions (Holzman, 2000) or sensory gating deficit (Freedman et al., 1997) as well as neuropsychological abnormalities such as impaired working memory *
Corresponding author. Tel.: +48-61-8475087; fax: +48-618480392. E-mail address: [email protected] (J.K. Rybakowski).
(Franke et al., 1992) or attentional deficits (Cornblatt and Malhotra, 2001) may serve as endophenotypic markers of genetic predisposition to schizophrenia. This was underscored by the fact that all these abnormalities have been reported to exist in a proportion of apparently healthy relatives of schizophrenic patients. Studying various eye movement disturbances, Crawford et al. (1998) found in relatives of schizophrenic probands with high saccadic distractibility greater eye movement disturbances than in relatives of probands with normal distractibility. In the study of Thaker et al. (1996), smooth pursuit abnormalities in persons with schizotypal and schizoid personality were more intense
0920-9964/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 9 9 6 4 ( 0 1 ) 0 0 3 5 7 - 7
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in those with familial occurrence of schizophrenia. Also, by studying relatives of schizophrenic patients, these authors observed more eye movement dysfunctions in relatives with a schizophrenia spectrum personality (Thaker et al., 2000). A similar observation was made by Ross et al. (1998a,b) where antisaccade abnormalities in relatives of schizophrenia were more marked with the familial type of disease and were correlated with disturbances of visuospatial working memory. On the other hand, Lencer et al. (2000) found that saccadic abnormalities may occur in relatives of both sporadic and familial schizophrenic patients. Staal et al. (2000), comparing patients with schizophrenia, their healthy siblings and healthy control subjects, found differences in cognitive functioning in the domains of abstraction, attention, executive functioning, spatial memory, and sensory-motor functioning. The schizophrenic probands were impaired on all these five domains, whereas their healthy siblings showed impairments on executive functioning and partially on sensory-motor functioning. For executive functioning, patients and healthy siblings seemed equally impaired as compared to control subjects. Data obtained by D’Amato et al. (1998) which explored, among others, executive functions by means of the Wisconsin Card Sorting Test (WCST) indicated that compared to controls, the performances of schizophrenic siblings on WCST were significantly impaired but they did not statistically differ from the schizophrenic ones. Faraone et al. (2000) found that relatives from multiplex families with schizophrenia had a higher degree of neuropsychological dysfunctions than patients coming from families with a lesser schizophrenic history. Studies on the first-degree relatives of schizophrenic patients (siblings or parents) make a valuable approach to verify the usefulness of the endophenotypic markers. In conjunction with molecular genetic methods such as candidate gene or genome scan, they may help on identification of specific genetic loci connected with schizophrenia. Here, we report our findings with eye movement and neuropsychological disturbances in first-degree relatives (parents) of schizophrenic patients. The aim of the study was to compare the results of oculomotor and neuropsychological tests as potential endophenotypic markers between firstepisode schizophrenic patients, both their parents as well as sex- and age-matched healthy controls.
2. Method 2.1. Subjects Twenty-one patients with first-episode schizophrenia (12 males and 9 females) including two female siblings aged 18 –33 (mean 22) years and both their parents (20 fathers and 20 mothers) aged 38– 69 (mean 48) years were studied. The duration of illness in schizophrenic patients ranged from 6 to 17 (mean 10) months and their mean education level was 12 years (range 8 –17). In schizophrenic patients, the tests were performed before starting pharmacological treatment, drug-free for at least 10 days: 18 patients were neuroleptic-naive at the time of study. In the group of parents, the mean education level was 13 years (range 8– 18). Seven parents studied (3 males, 4 females) had mental illness. Three subjects (2 males, 1 female) were diagnosed with schizophrenia, one female with unipolar depression with psychotic features, and one male with severe schizotypal personality disorder at the verge of psychotic decompensation. Two female parents had bipolar disorder. Six parents were under active treatment at the time of study and in these subjects, the tests were done on medication. An age- and sex-matched healthy control group for the parents was also included: there were 10 male and 10 female subjects aged 39 –69 (mean 49) years, with education level ranging from 10 to 18 (mean 13) years. 2.2. Eye movement measurements Eye trackings were measured by the infrared reflectometry method, using an Ober II system and Grenoble 96 computer program. Investigated subjects were seated in a darkened room in front of the computer screen with goggles (with infrared detectors) on their eyes, the distance between a 17-in. computer screen and the subject’s eye being 60 cm. The conditions for measurements, with sampling rate of 400 Hz and measurement time of 20 s, during two tasks: (1) point fixation on central position on the computer screen and (2) smooth pursuit at the moving point on Lisajou curves. The reason for choosing the Lisajou curves in Ober II system for the measurement of smooth pursuit movement was that
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these curves have constant mathematical characteristics but unlike regular sinusoidal curve, the subject investigated cannot predict the direction of the moving point. The subjects were instructed to keep their eyes fixed on the point during point fixation task and to observe the moving point during smooth pursuit task. Eye movement data were analyzed with CED Cambridge Spike 2 program, with script for eye movement analysis. The main indices of eye movement disturbances were the frequency (n/s) of saccades (catch-up, back-up, and intrusive saccades) occurring during each task and frequency (n/s) of square wave jerks (SWJ), regardless of their amplitude. The periods of artifacts or eye blinks were detected and not included in the analysis. The intensity of eye movement disturbances during fixation and during smooth pursuit was assessed on a 0– 3 scale. The following assessment criteria were applied: For fixation disturbances: 0 = no disturbances; 1 = minimal disturbances: intrusive saccades frequency: 0.01– 0.03; 2 = moderate disturbances: intrusive saccades frequency: 0.04 –0.07; and/or any SWJ; 3 = severe disturbances: intrusive saccades frequency > 0.07 and/or any SWJ. For smooth pursuit disturbances: 0 = no disturbances; 1 = minimal disturbances: intrusive saccades frequency < 0.005; and/or catchup and back-up saccades frequency < 0.005; no SWJ; 2 = moderate disturbances: intrusive saccades, frequency 0.005 – 0.026; and/or catch-up and back-up saccades frequency 0.003 – 0.05; and/or SWJ frequency < 0.005; 3 = severe disturbances: intrusive saccades frequency 0.026 –0.08; and/or catch-up and back-up saccades frequency 0.06 – 0.13; and SWJ frequency >0.005. 2.3. Neuropsychological assessment 2.3.1. The Trail Making Test (TMT) Part A of the test measures psychomotor speed. The results of part B reflect the ability to shift strategy and assess executive function and visuospatial working memory (Reitan, 1958). 2.3.2. The Stroop Color-Word Interference Test The first part of the test (part A), Reading Color Names in black (RNCb), measures verbal abilities and attention. The subject is asked to read as quickly as possible words (color names) printed with black ink on
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the white card. Second part (part B): Naming the Color of Word —different (NCWd)— measures verbal working memory and executive functions. The subject is asked to name color of each printed word. The color of the printed word is different from the color described by the word (Stroop, 1935). 2.3.3. The Wisconsin Card Sorting Test (WCST) The Wisconsin Card Sorting Test (WCST) is a standard test used to assess working memory and executive functions. The percentage of nonperseverative errors (NPE), the percentage of perseverative errors (PE), the number of correctly completed categories (CC), as well as the percentage of conceptual level responses (%CONC) were analyzed. The computer version of the WCST designed by Heaton et al. (1993) with instructions in Polish, was used in this research.
3. Results 3.1. Eye movement tests The results of oculomotor tests in patients, in their parents, and in control group are shown in Table 1. The values of eye movement tests obtained in healthy parents were placed between patients and the sex-matched control group for both fixation and smooth pursuit performance. There was a significant difference between patients and their 33 healthy parents, and also a significant difference between these parents and their 20 matched control subjects. In spite Table 1 The results of oculomotor tests in patients, in their parents, and in control group
Fixation Smooth pursuit
Patients, N = 21
Healthy parents, N = 33
Ill parents, N=7
Healthy controls, N = 20
1.8 ± 1.0* 2.2 ± 0.9*
1.2 ± 1.0*** 1.5 ± 1.2**
2.1 ± 0.9**** 2.3 ± 0.5
0.2 ± 0.4 0.4 ± 0.6
Difference between patients and healthy parents significant, * p < 0.05. Difference between healthy parents and their age-matched controls significant, ** p < 0.01, *** p < 0.001. Difference between ill and healthy parents significant, **** p < 0.05.
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of low number of ill parents, a significant difference was also observed between ill and healthy parents in fixation test and a trend for difference in smooth pursuit movements ( p = 0.09). In all groups (i.e., patients, their parents, and parents’ control group), no gender difference was found as to the values of oculomotor tests. A correlation was also analyzed between the intensity of eye movement disturbances in patients and those in either their fathers or their mothers, both healthy and ill. A highly significant correlation was obtained between the intensity of smooth pursuit disturbances in patients and in their fathers (Spearman r = 0.61, p = 0.003), and also between fixation disturbances in patients and smooth pursuit disturbances in their fathers (r = 0.46, p < 0.05). The respective correlation coefficients between patients and mothers were not significant (0.01 and 0.23). In the case of smooth pursuit disturbances, the difference between the magnitudes of correlation of father – patient and mother – patient was significant ( p < 0.05, two-tailed test). 3.2. Neuropsychological tests The results of neuropsychological tests in patients, in their parents, and in control group are shown in Table 2. There was a significant difference between patients and their 33 healthy parents in all subtests of TMT and WCST, however, such a difference was not observed in any part of the Stroop test. On the other hand, a significant difference between these parents and their matched control subjects was found only in Stroop B and in two indices of the WCST (CC and %CONC). A significant difference was obtained between healthy and ill parents in all indices, except for the WCST NP and %CONC. In any group, no gender difference was found as to the values of these neuropsychological tests, except for the WCST-CC in patients, with women scoring worse ( p < 0.05). The results of correlation analysis revealed a significant correlation between the degree of performance on WCST-CC and %CONC in patients and in their fathers (r = 0.49, p < 0.05 and r = 0.53, p = 0.01, respectively). The respective correlation coefficients between patients and mothers were not significant (0.10 and 0.02). The difference between father –
Table 2 The results of neuropsychological tests in patients, in their parents and in control group
TMT A TMT B Stroop A Stroop B WCST N-P WCST P WCST CC WCST %CONC
Patients, N = 21
Healthy parents, N = 33
Ill parents, N=7
46 ± 22** 133 ± 57** 30 ± 17 93 ± 29 16 ± 10**
31 ± 8 67± 28 25± 5 80± 35*** 7±5
43 ± 14****** 122 ± 28******* 31 ± 5***** 125 ± 36****** 10 ± 5
19 ± 13* 11 ± 7 18 + 7***** 3.8 ± 2.1* 5.1 ± 1.1**** 3.8 ± 1.1***** 54 ± 27* 69± 13**** 59 ± 13
Healthy controls, N = 20 28 ± 6 56 ± 24 23 + 5 61 ± 12 7±3 8±3 5.9 ± 0.4 80 ± 9
Difference between patients and healthy parents significant, * p < 0.01, ** p < 0.001. Difference between healthy parents and their age-matched controls significant, *** p < 0.01, **** p < 0.001. Difference between ill and healthy parents significant, ***** p < 0.05, ****** p < 0.01, ******* p < 0.001.
patient and mother – patient correlation magnitude was, however, not significant either for CC ( p = 0.2) or for %CONC ( p = 0.1) as analyzed by the two-tailed test.
4. Discussion The main finding of our study was a confirmation of validity for oculomotor and for some neuropsychological indices as possible endophenotypic markers of genetic vulnerability to schizophrenia. In apparently healthy parents of schizophrenic patients, these indices were significantly worse than in their matched controls. The results obtained corroborate those of other studies pointing to the presence of significant impairment on eye movement and neuropsychological tests in nonpsychotic relatives of schizophrenic patients (Crawford et al., 1998; D’Amato et al., 1998; Faraone et al., 2000; Lencer et al., 2000; Ross et al., 1998a,b; Staal et al., 2000; Thaker et al., 1996, 2000). In eye movement tests, the values of both fixation and smooth pursuit performance in schizophrenic parents were significantly different from both patients and healthy controls, however, in their magnitude they were much closer to schizophrenic patients than to
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control subjects. Among neuropsychological tests, the results of the Stroop B test were remarkable in that they significantly discriminated between healthy parents and matched controls but not between healthy parents and schizophrenic patients. However, the lack of difference between schizophrenic patients and their healthy parents might be due to age differences between these two groups. This was further supported by the fact that ill parents scored significantly worse on Stroop B test compared both with their healthy counterparts and with schizophrenic offspring. In ill parents, duration of the illness could also contribute to their poor results on this test. A significant difference between healthy parents and their matched controls obtained in the WCST-CC and the %CONC may suggest that, in addition to Stroop B, the performance on these indices may involve a genetic component associated with predisposition to schizophrenia. Such a feature of the %CONC was further supported as the values on this did not differentiate between parents with or without mental illness. There was a difference between ill and healthy parents on most neuropsychological and neurophysiological tests. The most obvious explanation is that part of the deficit in ill parents may be disease-linked as part of developing the full disease itself. The second possibility is that the ill parents may have a higher genetic liability to schizophrenia than the healthy parents. An unexpected finding of our study was the correlation obtained between the intensity of eye movement disturbances in patients and that in their fathers but not in their mothers. Similarly, the patients – fathers (but not the patients – mothers) correlation was obtained with some WCST indices (CC and %CONC), namely those also shown to be the best discriminators between schizophrenics’ parents and their healthy controls. One interpretation of this finding may be that gender differences in schizophrenia may involve an imprinting phenomenon where some genes influencing behavior may either be repressed or expressed depending on which parent they are inherited from (Reik et al., 2000). Furthermore, a predominance of paternal transmission in schizophrenia was shown in two recent studies. Husted et al. (1998) demonstrated that anticipation in familial schizophrenia was significantly greater with paternal than with maternal transmission. Also, the effect of parental age
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on the risk of schizophrenia was shown for fathers but not for mothers (Malaspina et al., 2001). To date, only one study showed possible mapping of eye movement disturbances to a locus on chromosome 6, using genomic scan for the specific region of 6p21-23 (Arolt et al., 1996). Further testing of possible linkage of eye movement disturbances to specific markers on chromosomes 8, 9, 20, and 22 performed by these authors yielded negative results, although they confirmed their previous findings with chromosome 6 (Arolt et al., 1999). Recently, we found a significant association between the intensity of eye movement disturbances (fixation and smooth pursuit) and the Ser-9-Gly polymorphism of dopamine D3 receptor (DRD3) gene both in schizophrenic patients and healthy subjects, where allele 1 (serine) was connected with worse performance (Rybakowski et al., 2001). An association was also recently reported between the Val-158-Met polymorphism of gene for catechol-O-methyl-transpherase (COMT), an enzyme responsible for dopamine metabolism, and the performance on the Wisconsin Card Sorting test in both schizophrenic patients and healthy control subjects, with allele 1 (valine) determining the lower score (Egan et al., 2001). The results of molecular genetic studies applied to such endophenotypes as eye movement and neuropsychological performance suggest that the genetic component for predisposition to schizophrenia may involve an altered dopaminergic activity in prefrontal cortex. This is where both DRD3 receptors and COMT activity are located and also the region mostly connected with the pathophysiology of both oculomotor and neuropsychological tests used in our study. Such a notion was also corroborated by the neuroimaging study of eye movement disturbances in relatives of schizophrenic patients performed recently by O’Driscoll et al. (1999). In schizophrenics’ first-degree relatives exhibiting eye movement disturbances, the features of subtle frontal dysfunction were found and were proposed by these authors as a biological substrate of the genetic predisposition to schizophrenia.
Acknowledgements This work was supported by Polish Committee of Scientific Research (KBN) Grant No. 4P05B 06512.
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