Researchers from the New York State Psychiatric Institute compared the birth records of approximately 88,000 individuals born in Israel between 1964 and 1976. They found 658 subjects who were diagnosed with schizophrenia or a related psychotic disorder and looked at the number of reported psychotic episodes at age 21. They found that among those whose fathers were younger than 25 years at the time of conception, 3.5/1,000 people experienced a psychotic episode. Among those whose fathers were older than 50 years at the time of conception, 11.4/1,000 experienced a psychotic episode. The researchers took into account maternal age, education, socioeconomic status, and ethnicity to rule out other possible explanations for the strong correlation between increased paternal age and the risk of schizophrenia.

Researchers are now exploring gene mutations in the fathers' sperm that may be responsible for the association. Such a provocative finding needs to be independently confirmed before researchers can look at its possible implications.