Study links autism risk to dad’s age

LONDON— A father’s age, not a mother’s, when a baby is conceived is the single largest factor in the risk of passing on new gene mutations to children and may help explain why childhood autism rates are rising, scientists said Wednesday.

In a study that turns conventional thinking on its head, researchers sequenced the genomes of 78 Icelandic families with children diagnosed with autism or schizophrenia and found a father’s age was crucial to the genetic risk of such disorders.

“Conventional wisdom has been to blame developmental disorders of children on the age of mothers,” said Kari Stefansson, chief executive of the private firm deCODE Genetics in Reykjavik, whose work was published in the journal Nature. “(But) our results all point to the possibility that as a man ages, the number of hereditary mutations in his sperm increases.”

He said this age-linked increase in mutations proportionally increased the chance a child might carry a harmful mutation that could lead to conditions like autism and schizophrenia.

“It is the age of fathers that appears to be the real culprit,” he said.

The study found an average of two more new gene mutations appeared in offspring for every year of increase in a father’s age — meaning the number of new mutations passed on by fathers would double every 16.5 years after puberty.

However, it was not possible to say at what age this could become a concern for a man, since there are so many other factors involved.

Women who conceive later in life are at higher risk of having babies with Down syndrome and other rare chromosomal abnormalities, but Stefansson said his study showed men transmitted far more new gene mutations to children.

Richard Sharpe, a professor at the University of Edinburgh’s Centre for Reproductive Health who was not involved in this research, said its results suggested men should recognize there is a price to pay for remaining fertile into old age.

“The price is paid by their children because the older your father at conception, the greater the number of gene mutations you inherit from him,” he said.

The finding jibes with results of three U.S. studies that found spontaneous mutations could occur in egg or sperm cells that raised the risk of autism, and that fathers were four times more likely than mothers to pass on these mutations.