Schizophrenia 103
hyperactivity disord er). These symptoms should not be attributed to schizophrenia with-
out due consideration of the more common disorders of childhood. Childhood-onset cases
tend to resemble poor-outcome adult cases, with gradual onset and prominent negative
symptoms. Children who later receive the diag nosis of schizophrenia are more likely to
have experienced nonspecific emotional-behavioral distur bances and psychopathology,
intellectual and language alterati ons, and subtle motor delays.
Late-onset cases (i.e., onset after age 40 ye ars) are overrepresent ed by females, who
may have married. Often, the course is ch aracterized by a predom inance of psychotic
symptoms with preservation of affect and soci al functioning. Such late-onset cases can still
meet the diagnostic crit eria for schizophrenia, but it is not yet clear whether this is the
same condition as schizophrenia diagnosed prio r to mid-life (e.g., prior to age 55 years).
Risk and Prognostic Factors
Environmental. Season of birth has been linked to the incidence of schizophrenia, in-
cluding late winter/early spring in some locations and summer for the deficit form of the
disease. The incidence of schizophrenia and related disorders is high er for children grow-
ing up in an urban environment an d for some minority ethnic groups. 
Genetic and physiological. There is a strong contribution  for genetic factors in deter-
mining risk for schizophrenia, although most individuals who have been diagnosed with
schizophrenia have no family history of psyc hosis. Liability is conferred by a spectrum of
risk alleles, common and rare, with each allele contributing only a small fraction to the to-
tal population variance. The risk alleles identi fied to date are also associated with other
mental disorders, including bipolar disorder, depression, an d autism spectrum disorder.