Older fathers are more likely to have children with schizophrenia, research suggests.
Men aged 50 or over are three times more likely to father a child with the illness compared to men of 27 or under. And men aged between 45 and 49 are twice as likely to have a child with schizophrenia.
The scientists behind the research estimate that as many as one in four cases of schizophrenia could be caused by the father being old. Their study looked at records of almost 56,000 people born in Jerusalem between 1966 and 1986, and compared them to data from the Israel Psychiatric Register, which is part of the Israeli Ministry of Health.
Lead researcher Professor Dolores Malaspina, of the Columbia University College of Physicians and Surgeons, said her findings showed "a man has a biological clock too".
She said: "Men should be aware of the risks when they do their family planning." As men get older, their sperm reproduces through division. Each successive division introduces a slight risk of error in the genetic material of the new sperm, which is then passed on to the child.
Mutations are tiny, and difficult to spot without knowing in advance what mutations to look for.
Any abnormalities in women's eggs can be picked up more easily, as almost all divisions in a woman's eggs occur before she is born. Egg abnormalities also usually involve larger chromosomal changes, and are therefore easier to test for.
Schizophrenia is the most common serious mental illness. It affects one person in a hundred at some time in their life, and the rate is the same in every country.Most people are affected when they are in their late teens or early 20s, though it can start at any age. Schizophrenia is a psychotic disorder. Symptoms include hallucinations and delusions.
Genetic and environmental factors are thought to be responsible.
An additional finding in the study was that the longer parents had been married, the more the risk of schizophrenia decreased. But the benefit does not cancel out the risk associated with a father's age. The researchers said further work was now needed to be done to identify exactly why the sperm mutations occur, and how they can be spotted.