Neuropsychological deficits are considered endophenotypes for schizophrenia, because they are not only found in patients but also in many of their unaffected relatives, albeit in attenuated form. It is not yet clear which of these deficits in relatives are related to genetic or to environmental causes. We tested effects of inferred genetic liability for schizophrenia on neurocognitive variables to address this problem.

Twenty-eight patients with schizophrenia, 129 non-affected biological parents and 143 matched controls were assessed with an extensive neuropsychological test battery including tests of attention, memory, executive functioning and motor soft signs. Twenty-two parents had an ancestral history of schizophrenia and therefore were hypothesized to be more likely than their spouses without such a history (n = 17) to carry a genetic risk for schizophrenia.

Unaffected parents of schizophrenic patients showed significant deficits in a wide array of neuropsychological tasks and task domains. However, comparison of more likely and less likely carriers of illness-related genes showed specifically attentional and executive functioning, but not memory, to vary with degree of inferred genetic loading.

Attentional and executive (frontal) impairments vary with genetic loading for schizophrenia and can be considered true endophenotypes for this disorder. Consequently, these functions are particularly suited to evaluate the functional impact of candidate genes for schizophrenia in future studies.