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

Objective: 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. Method: 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. Results: 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). Conclusion: 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.