Prospective parents have long worried about the effects their advancing age might have on their children, and rightfully so; babies born to older parents have higher rates of autism, schizophrenia, and Down syndrome. But teenage dads may have reason to worry as well. A new study published yesterday in Proceedings of the Royal Society B shows that teenage dads pass on more genetic mutations to their children than previously thought.
The researchers looked at DNA samples from 24,097 subjects across Europe, the Middle East, and Africa. The samples were obtained through routine paternity tests as well as immigrants seeking to prove a relation to family members in Britain. The fathers ranged in age from just 12 years old to over 70, and the mothers between 10 and 52. The team parsed the subjects' DNA for short repeating segments called microsatellites, which mutate at a rapid pace as cells divide and thus can be traced from parent to child. Because the microsatellites only mutate when cells replicate, they functioned as a “cell-cycle counter” for the researchers, tallying the number of cell divisions that had occurred since the sample originated.
The researchers found that the mutation rate in teenage boys was higher than all but the oldest fathers; the mutation rate in older fathers was only 1.3 times that of their teenage counterparts.
Teenage dads had a six-fold higher mutation rate compared to teenage moms. “They should have been similar at the onset of puberty,” says Peter Forster, a geneticist at the University of Cambridge and lead author on the study.
Forster believes that the problem arises during the production of sperm cells, a process called spermatogenesis. Women are born with all the eggs they need to procreate, so the mutation rate in females remains relatively stable over the years. (Older women have usually trouble conceiving and have a higher risk of birth defects due to other types of mutations, rather than the kind acquired during cellular replication.) Males, on the other hand, need to continuously create a supply of sperm cells, which leads to higher rates of mutations as the cells that give rise to sperm divide. The team expected to find a much higher rate of mutation in older males, and a relatively low and stable mutation rate in males and females around puberty.
Instead, the researchers found that the mutation rate in teenage boys was higher than all but the oldest fathers; the mutation rate in older fathers was only 1.3 times that of their teenage counterparts. The non-linear relationship between mutation rate and age revealed that sperm production during puberty is still not fully understood, according to the authors.
The development of egg cells in women is well understood, but “it is difficult to study the details of spermatogenesis in humans,” Forster says. “It is useful to have new and non-invasive tool, in the form of DNA microsatellites, to study the ‘ancestry’ of cells involved in spermatogenesis and indeed in all tissues and tumors.”
Though the increased risk in having a child with a birth defect is still very low, it’s just another reason to provide teens with access to sex education and contraception.