Approximately 60% of subjects with schizophrenia present minor neurological signs (neurological soft signs, NSS), which include abnormalities in sensory and motor performance indicative of a non-specific cerebral dysfunction. These are also present in healthy individuals and relatives of patients with psychosis, at significantly lower rates. The excess of NSS in psychosis may be a potential endophenotype for this disorder, and reflect the same neurodevelopmental brain dysfunction that also underlies the cognitive deficits consistently reported in psychosis. To establish whether neurological and cognitive dysfunction meet the essential criterion required for a refined endophenotype for psychosis, the association with the illness, we explored evidence that certain neurological and cognitive deficits co-occur in affected individuals. This evidence suggests that signs of motor dysfunctions may be specific to patients with psychosis, in whom they are associated with dysfunction in cognitive tasks requiring motor skills. Thus, they may form a promising candidate endophenotype for psychosis.
