Neuropathological, obstetrical, and epidemiological evidence increasin
gly suggest that some cases of adult-onset schizophrenia have prenatal
or neonatal etiological roots. We evaluated the developmental histori
es of 23 monozygotic twin pairs discordant for schizophrenia to determ
ine when they markedly and permanently began diverging from each other
in motor skills or unusual behavior. Seven of the twins (30%) who lat
er developed schizophrenia had become permanently different from their
cotwins by age 5 years. The early divergence group differed from the
others by multivariate tests (p = 0.002) for within-twin pair effects
and by univariate tests for physical anomaly scores (p = 0.01), total
finger ridge counts (p = 0.001), family history of psychosis (p = 0.00
4), and serious perinatal complications or low birth weight (p = 0.05)
. It is concluded that some cases of adult-onset schizophrenia are ass
ociated with prenatal events, which may include neurodevelopmental abn
ormalities or specific insults such as anoxia or infectious agents.