Heritability of age of onset of psychosis in schizophrenia

Schizophrenia is a genetically complex illness with heterogeneous clinical presentation, including variable age of onset. Inthis study, the heritability, or proportion of variation in age of onset of psychotic symptoms due to genetic factors, was estimated using a maximumlikelihood method. The subjects were 717 members of families with more than onemember affected with schizophrenia from Mexican and Central American populations. Age of onset of psychosis was determined by best-estimate consensus diagnosis based on the Diagnostic Interview for Genetic Studies, Family Interviewfor Genetic Studies, and each subject's medical records. Mean age of onset was 21.44 years (SD 8.07); 20.55 years for males (SD 6.90), and 22.67 for females (SD 9.34). Variance components were estimated using a polygenic model in the SOLAR software package. The sex of the participant was a significant covariate (P=0.010) accountingfor 0.02 of the total variance inage ofonset. The heritability of age of onset of psychosis was 0.33 (SE=0.09; P=0.00004). These findings suggest that genetic factors significantly contribute to the age of onset of psychotic symptoms in individuals with schizophrenia and that sex influences this trait as well.