Gender differences in premorbid cognitive performance in a national cohort of schizophrenic patients.

Despite significant research, there are still inconsistent findings regarding gender differences in cognitive performance in individuals already diagnosed with schizophrenia; studies have found that males suffering from schizophrenia are more, less or equally impaired compared with females. Gender differences in cognitive performance in individuals suffering from schizophrenia may be influenced by gender differences in premorbid cognitive performance; the very few and very small N studies published indicated that males have a poorer pre-morbid cognitive performance than females. This study examined the gender differences in premorbid cognition, utilizing cognitive assessments performed on female and male adolescents before induction into military service. The Israeli Draft Board Registry, which contains cognitive assessments equivalent to IQ scores on 16-18 year old Israeli adolescents, was linked with the Israeli National Psychiatric Hospitalization Case Registry, which records all psychiatric hospitalizations in the country. Scores on premorbid cognitive performance in schizophrenia were examined in 90 female-male case pairs matched for school attended as a proxy for socio-economic status. The mean age of first hospitalization was 20. 1+/-1.8 years of age for males and 19.6+/-1.8 years of age for females. A repeated-measures ANCOVA with age of first hospitalization and years of formal education as covariates, and controlling for gender differences in cognitive performance in healthy adolescents, revealed a significant difference in pre-morbid cognitive performance between males and females on all four cognitive measures [F(1,87)=8.07, P=0.006] with females scoring lower (worse) than males. In this national cohort, pre-morbid cognition was poorer in female, compared with male, adolescents who will suffer from schizophrenia in the future, a result consistent with some, but not all, similar studies. These results may be valid only for patients with first hospitalization around age 20. Hence, gender differences in premorbid cognition should be taken into account when assessing gender differences in cognition in schizophrenia.