Premorbid and current general intellectual function in familial and non-familial schizophrenia : a study of schizophrenic patients and their first-degree relatives

Abstract

Objective: To estimate premorbid and current general intellectual levels in schizophrenic patients from multiply and singly affected families, their relatives and normal control subjects.

Methods: Premorbid and current general intellectual function was investigated in two groups of schizophrenic patients (familial/non-familial), their first-degree healthy relatives and normal controls (251 subjects in total). Premorbid and current general intellectual levels were examined using the National Adult Reading Test (NART) and Canavan's (1986) five subtest short form (Vocabulary, Comprehension, Similarities, Block Design, Object Assembly) of the Wechsler Adult Intelligence Scale - Revised (WAIS-R).

Results: All groups scored within the average or high average IQ range. Familial schizophrenics performed significantly worse than controls (z = 3.59, P < 0.0001 ) and their relatives (z = 3.48, P<0.0001) on current IQ. Non-familial schizophrenics performed significantly worse than controls and their relatives on both premorbid (non-familial vs. controls z=2.27, P=0.02; non-familial vs. relatives z=2.52, P=0.01) and current IQ (non-familial vs. controls z=4.58, P<0.0001; non-familial vs. relatives z=4.99, P<0.0001). Neither of the relative groups differed significantly from controls on either measure.

Conclusions: (1) As has previously been suggested (Aylward, 1984; Goldberg et al., 1990) schizophrenic probands score lower, even when performing within the normal limits, than would be expected from their genetic and environmental endowed potential when compared with the performance of their relatives. (2) The lower premorbid IQ found in the non-familial, but not the familial, groups might suggest a different underlying aetiological mechanism.