Neurological and morphological anomalies and the genetic liability to schizophrenia: a composite phenotype.

Background: Neurological soft signs (NSS) and minor physical anomalies (MPA) are frequent in patients with schizophrenia and their biological relatives. We examined whether the NSS and MPA are related to the genetic loading in schizophrenia.
Methods: Patients with schizophrenia (DSM-IV) (n=61), nonpsychotic parents of these patients (n=76) and healthy comparison subjects (n=44) took part in the study. Parents were further classified as "presumed carriers" of the genetic loading (n=26) if they had a second relative with schizophrenia in their ascendants and/or collaterals (first or second degree) or as "presumed noncarriers" (n=50). NSS and MPA were compared in these groups.
Results: A multivariate analysis indicated that total NSS and MPA scores, adjusted for age and gender, were significantly related to group status. Univariate tests showed higher scores in motor coordination and integration subscores (p=0.005 and 0.008, respectively) in presumed carriers than in presumed noncarriers. In addition, a discriminant function analysis based on total NSS and MPA scores correctly classified 71% of nonpsychotic parents in presumed carriers or presumed noncarriers.
Conclusions: Neurological impairments and slight morphological anomalies seem to be associated with the genetic risk for schizophrenia, even when the disease itself is absent. Their presence might be a valuable composite intermediate phenotype for genetic studies.