[Vulnerability to schizophrenia. I: Familial nature of of neuropsychologic indicators]

The existence of a genetic background is now a well admitted notion in schizophrenia, but some individuals at genetic risk for that disease could never manifest it at a clinical level. However, several vulnerability models could help us to identify such individuals. According to them, when similar perturbations at a given test are observed both in clinically stable schizophrenics and their nonschizophrenic first degree relatives, this test could be qualify as an indicator of the vulnerability to schizophrenia. In literature, that seems the case for several neuropsychological tasks, exploring attentional abilities (degraded version of the Continuous Performance Task [DS-CPT], and Span Of Apprehension task [SOA]) and executive functions (Wisconsin Card Sorting Test [WCST]). Our study was undertaken to replicate literature data and to further explore the relationship between these three neuropsychological markers. For that purpose, performances at DS-CPT, SOA and WCST were assessed among 18 clinically stable schizophrenics, 18 of their biological full siblings and 15 unrelated control subjects matched with the two others groups for several socio-demographic factors. Comparisons were performed by non parametric analysis (Kruskal-Wallis one way ANOVA, and Mann-Whitney). Compared to controls, the siblings group performances were significantly impaired on the three tasks, while they did not statistically differ from the schizophrenic ones. No relationship was observed between the markers, except for the "d'" index at DS-CPT and the number of successfully performed categories at the WCST. Results from the sibling group suggested that the observed impaired neuropsychological performances may actually represent indicators of the genetic vulnerability to schizophrenia. Moreover, the generally admitted relationship between WCST poor performances and an impairment of the prefrontal cortex, lead us to hypothesize some role of this brain area in schizophrenia vulnerability.