The median lifetime morbid risk for schizophrenia is 7.2 per 1000 people. The male-to-female risk ratio is 1.4:1. A connection may exist between later onset in females and higher pre-morbid functioning. It appears that the incidence and prevalence of schizophrenia vary depending on race and geographic location. Patients with schizophrenia have a higher mortality than the general population due to physical illness (e.g., cardiovascular diseases and cancers), accidents, and suicide.
The age of onset is usually <25 years for males and <35 years for females. It has been reported that more affected people are born in the winter versus the spring or summer seasons, but these data are controversial. Additionally, a higher disease incidence has been reported in urban and low-income populations when compared with rural and higher-income groups. The incidence and prevalence appears to increase over time. There is a reported higher incidence in migrant populations, which appears to persist into the second generation. While the prevalence of psychotic disorders in the 10- to 18-year-old age group is relatively low at around 0.4%, the prevalence of schizophrenia in 10- to 18-year-olds hospitalised for psychiatric causes is 25%, with an exponential increase over the adolescent years.
Cognitive deficits tend to precede the development of schizophrenia, persist for the whole duration of illness, and be closely tied to functional outcomes.
There appears to be a significant increase in the risk of schizophrenia in children of fathers age ≥30 years.
This includes fetal growth retardation, maternal infection, blood group incompatibilities, perinatal hypoxia, and premature delivery.
Heavy marijuana use may increase both the vulnerability to schizophrenia and the likelihood of developing the disorder (odds ratio of around 2.2 to 2.8). Cannabis use following onset of first-psychosis is associated with both an increased risk of relapse and non-adherence with antipsychotic medication. The results of one prospective analysis suggest that up to 36% of the negative effects of continued cannabis use in patients with psychosis are due to a reduction in concordance with medication.
A longitudinal, long-term follow-up cohort study looked at adolescents at ultra-high risk of developing psychosis. Low IQ was the single neurocognitive factor that discriminated the ultra-high risk patients who developed psychosis from those who did not, and from controls.
Soft neurological signs (minor abnormalities in motor performance on clinical examination; for example, rigidity, gait imbalance, tremor) differentiate individuals at ultra-high risk for psychosis. These signs also correlate with an increase over time in the severity of negative symptoms.
Evidence suggests a link between psychological stressors and disease onset.
Connected with an increased risk of psychosis in adulthood.
The evidence is debatable.
Outcome of schizophrenia has been inversely correlated with mean daily temperatures.
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