Autism and Older Fathers
Last reviewed and revised on June 17, 2011
By Michael Craig Miller, M.D.
A study published in the September, 2006 issue of the Archives of General Psychiatry may give older prospective fathers pause before plunging into biological parenthood. The authors found a significant increase in the risk of autism and similar disorders as fathers got older.
The risk was smallest for children of fathers younger than 20 and greatest for children of fathers older than 50. A man in his 40s, for example, was almost 6 times as likely to have an autistic child as a man age 20. This relationship held even after researchers adjusted the results for the year of the person's birth, their socioeconomic status, or the mother's age.
This is not the first discovery of its type. Health care professionals have long known that as parents age, the risk of giving birth to a child with certain illnesses goes up. Older mothers, for example, are more likely to have a child with Down syndrome. In recent years, studies have revealed a link between aging fathers and schizophrenia.
The Archives study took advantage of the extraordinarily complete health records of over 300,000 Israeli men and women. They underwent a complete health assessment when they were 17-year olds, prior to entering military service. Using this database, researchers were able to determine the incidence of autism in the population. The researchers had access to intellectual, medical and psychiatric evaluations of almost all Israeli boys and three-quarters of girls. (Their identities were kept secret, however.) For most individuals, the father's age at birth was known.
Although boys were more likely to develop autism than girls, the risk for girls also increased as fathers got older. When fathers were young, about 1 in 6 children with autism were girls. After fathers passed the 40 year-old mark, the proportion of girls with autism rose to about 1 in 3. This suggests that the genetic factors in play for offspring of older fathers are different from those for offspring of younger fathers.
All children inherit genetic material in equal amounts from both parents. In the case of autism, scientists think that the genetic material in the sperm of these older fathers has somehow become altered in harmful ways. These flaws make the child more vulnerable to developing the disease.
According to one theory, mutations (changes) are more likely to develop as men get older. Germ cells give rise to sperm throughout a man's life. These cells make copies of themselves and after several decades, the germ cells are copies of copies of copies. A second theory suggests that the offending genes passed down by older men are not properly marked or "imprinted." Accurate marking which establishes whether a gene is from the father or the mother determines if it will be active or not. If there is an error, the gene may function abnormally.
It's true that medical technology and general improvements in health have made life much more enjoyable for people in middle to late life. Maybe 50 is the new 30 when it comes to some aspects of aging. But a healthy and active lifestyle does not make 50-year-old sperm the new 30-year-old sperm.
The increased risk of passing on any genetic vulnerability to a child is significant when you are older. When it comes to autism, however, the numbers are sobering. A man younger than 30 has no more than a 1 in 1,000 chance of fathering a child with autism. But the risk bumps up to approximately 3 in 1,000 for a man in his 40s and 5 in 1,000 above age 50. If a father in his fifties has a son, the risk of autism may approach 1 in 100.
This study has important implications for what causes autism, but it also has limitations:
Until recently, health care professionals have focused almost exclusively on the mother's age as a risk factor for health problems in the child. But we now know that the father's age also adds to the risk of potentially devastating diseases. And there is no practical way to detect these illnesses during pregnancy. For those weighing the risks, the decision can be wrenching. Adoption and in some instances a sperm donation may be acceptable alternatives to older fathers wanting to build a healthy family.
Michael Craig Miller, M.D. is Editor in Chief of the Harvard Mental Health Letter. He is also associate physician at Beth Israel Deaconess Medical Center and assistant professor at Harvard Medical School. He has been practicing psychiatry for more than 25 years and teaches in the Harvard Longwood Psychiatry Residency Program.