Sibling characteristics and early onset psychoses among the young adolescent patient population.

We investigated the relationship between sibling characteristics (birth order, number of siblings and birth interval) and early onset psychosis among adolescent psychiatric inpatients and their mentally healthy controls. A short birth interval of 1-2 years to the nearest sibling was more common among adolescents with schizophrenia and schizophrenia spectrum psychoses and differed significantly from healthy controls (p = 0.037). A large family (at least 6 children in family) was more common among adolescents with psychosis NOS than among healthy controls (p = 0.035). The birth order among young adolescents with any subtype of psychosis did not differ from healthy controls. Sibling characteristics may be contributing factors in the multifactorial aetiology of schizophrenia and other psychotic disorders. Further studies are required to determine whether sibling characteristics reflect other unknown environmental factors.