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When it comes to having children, the biological clock isn't ticking down just for women.
Men also run the risk of having offspring with chromosomal birth defects if they postpone fatherhood for too long, according to a Dutch study.
The findings are based on 118 children whose genome, or genetic code, was analyzed at Radboud University Nijmegen Medical Centre in the Netherlands.
"We were looking at a specific form of genetic mutation which we find in some children with an intellectual disability," explained the lead researcher, Jayne Hehir-Kwa.
In those cases, both parents are healthy but the child is born with chromosomal abnormalities in which sequences of DNA are missing, repeated, inverted or misplaced. As DNA is packed into 23 pairs of chromosomes, with half the genetic material originating from the mother and half from the father, the researchers were trying to determine which parent was the source of the defective DNA. "We found there was a strong bias towards the father's DNA," said Dr. Hehir-Kwa.
The study revealed that in 90 of the 118 children the mutations were linked to the fathers. The results, published in the Journal of Medical Genetics, also showed that the men tended to be older than other Dutch fathers when their children were conceived. "Some were in their 40s and a few above 50," she said.
Dr. Hehir-Kwa suspects that the DNA problems arise from faulty sperm production in the older men.
Earlier research has also suggested that children of older men may be at higher risk for certain diseases such as schizophrenia. But "this is the first study linking these genetic mutations for intellectual disability to the father's age," said Dr. Hehir-Kwa.
The degree of intellectual disability in offspring varies, reflecting the fact that the children don't have identical chromosomal abnormalities.
In the case of Down Syndrome, which is associated with older mothers, one entire chromosome is duplicated. By contrast, chromosomal defects leading to intellectual disabilities "are randomly dispersed throughout the genome," said Dr. Hehir-Kwa.
Although a lot more work needs to be done, researchers may be able to develop a prenatal test for some intellectual disabilities, which occur at a rate of 1 per cent of births.
"The [genetic]variants we looked at explain about 10 per cent of that 1 per cent," she said.