Single or multiple familial cognitive risk factors in schizophrenia?

The fact that relatives of patients with schizophrenia display subtle cognitive abnormalities suggests genetic transmission of an underlying cognitive endophenotype. It was examined to what extent the cognitive abnormalities that discriminate patients and relatives from controls do so independently of each other, and independent of IQ. Neuropsychological measures were assessed in 50 patients with schizophrenia, 50 first-degree relatives of patients with schizophrenia, and 50 healthy controls. The assessment focused on episodic memory, attentional span, simple and complex speed of information, and semantic memory. Factor analysis of the cognitive test results yielded four factors reflecting speed, episodic memory, working memory, and semantic fluency. Performance of the relatives was intermediate to that of the patients and the controls after adjustment for age, sex, educational level, and IQ. For both patients and relatives, speed of information processing, working memory, and episodic memory independently discriminated from control performance, with a similar pattern in the order of the size of the effects. The results suggest the existence of more than one familial cognitive risk factor for schizophrenia. Independent familial cognitive risk factors may represent separate causal influences or separate indicators of risk related to the same genetic mechanism.