Men may have a biological clock as women do; U.S. researchers say children of middle-age fathers are at higher risk of mental illness such as autism. Brian M. D'Onofrio of Indiana University, Bloomington, and colleagues analyzed medical and public records of some 2.6 million people born in Sweden from 1973 to 2001. They estimated the risk of psychiatric problems. Sweden keeps detailed medical records so the father's age for each birth is noted and the researchers were able to track each child's medical history over time, as well as that of siblings and other relatives. The study, published in the Journal of the American Medical Association Psychiatry, compared the mental health of siblings born to the same father and found a clear pattern of increased risk of mental illness with increasing paternal age. Siblings born to fathers age 45 years and older were at higher risk for autism, attention deficit/hyperactivity disorder, psychosis, bipolar disorder, suicide attempts, substance abuse, failing a grade in school and low educational attainment compared with siblings born to fathers ages 20 to 24, the study found. Compared with the children of the young fathers, ages 20 to 24, those born to men age 45 and older had about twice the risk of developing psychosis, more than three times the likelihood of receiving a diagnosis of autism, and about 13 times the chance of having a diagnosis of attention-deficit hyperactivity disorder, The New York Times reported. Children of older fathers also tended to struggle more with school, fail grades and suffer from substance abuse, the study said. The researchers said any increased risk due solely to paternal age is most likely a result of the accumulation of genetic mutations in sperm cells. Previous research suggests older fathers at childbearing are associated with genetic mutations during the development of sperm, which may cause an increased risk of child psychiatric, intellectual and academic problems.