Do schizotypal symptoms mediate the relationship between genetic risk for schizophrenia and impaired neuropsychological performance in co-twins of schizophrenic patients?

BACKGROUND: Neurocognitive deficits and symptoms of schizotypal personality disorder are both elevated in the first-degree relatives of schizophrenic patients, but their relationship to each other and their potential common genetic source remain unclear. METHODS: Fifty unaffected co-twins of schizophrenic patients and 123 control twins were assessed with a neuropsychological battery and structured clinical interviews. RESULTS: Working memory was influenced by genetic risk for schizophrenia but not schizotypal symptoms. Nearly all other domains were influenced by schizotypy symptoms but only in the co-twins of schizophrenic patients. Schizotypy symptoms in the absence of a family history did not seem to be related to impaired neurocognitive functioning. CONCLUSIONS: Schizotypy symptoms in those with genetic risk for schizophrenia are associated with increased risk for cognitive deficits. Some neurocognitive deficits might covary with subpsychotic symptoms due to a shared genetic factor. Community-ascertained schizotypal individuals might not be appropriate for modeling underlying genetic risk for schizophrenia.