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Background: Studies have shown that patients with Schizophrenia (SZ) or Bipolar Disorder (BP) have cognitive deficits. Several studies have also reported that offspring of SZ or BP parents performed worse, on average, than non at risk offspring. However, only a minority of at risk offspring will develop SZ or BP later on. Hence, the reported deficits concerning them may represent a mixture of larger and smaller deficits which, respectively, would refer to those subjects who would eventually convert versus those who never would. The present study addresses this issue by attempting to separate the at-risk offspring into two subgroups according to their cognitive performance.
Methods: Our sample was composed of 131 at risk offspring from 6 to 24 years old assessed on five cognitive domains: Processing speed, Verbal memory, Visual Memory (VISEM), Working memory, and Executive functioning. A hierarchical clustering analysis was performed on all five domains. The pseudo F statistics and Pseudo T square-index were used to estimate the number of clusters. Then each cluster found was compared to a matched sample of 131 healthy control subjects using a two way ANOVA.
Results: Two clusters were revealed: a cluster of at risk offspring that showed a cognitive profile almost identical to that of control subjects, and another cluster that performed much worse than the healthy controls with effect sizes often exceeding those previously seen in the literature, and reaching 2.3 for VISEM.
Conclusion: To our knowledge, this is the first study highlighting a very healthy cognitive performance for a subset of at risk offspring, but a worse than known performance in the remaining offspring. Still, further longitudinal studies are needed to investigate whether these findings are associated with the transition to a major psychiatric disorder such as SZ or BP.
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