Increased number of offspring in first degree relatives of psychotic individuals: a partial explanation for the persistence of psychotic illnesses

Abstract

As patients with psychotic illness have fewer offspring than controls, the persistence of psychotic illness is puzzling. We hypothesized that unaffected first-degree relatives of patients have more offspring than controls. Probands were 4904, individuals with non-affective psychotic disorders identified from a hospitalization registry. Unaffected first degree relatives and matched controls were identified from the Israeli Population Registry. The number of offspring of unaffected parents, biological siblings and controls was ascertained. Unaffected parents of psychotic patients had more offspring/person than controls; 4.5 +/- 2.7 vs. 3.4 +/- 2.2, P = 0.000. Unaffected parents from familial psychosis families (more than one affected family member) had 1.83 more offspring than controls; unaffected parents from non-familial psychosis families had 0.97 more offspring than controls (both P < 0.001). These findings might imply that genes which increase susceptibility for schizophrenia may be associated with increased number of offspring, perhaps supplying a partial explanation for the persistence of psychosis.