A recent landmark study published in the journal Nature showed that older fathers were more likely than younger ones to pass on a gene mutation that is responsible for the risk of developing autism and schizophrenia. The researchers in the study reasoned that random mutations were more present as the father grew older, which provided a plausible explanation for the surging rate of autism observed in recent decades along with the average increase in age of conceiving fathers. Autism spectrum disorders can range from relatively mild symptoms, such as those seen in people with Asperger’s Syndrome to people with severe mental retardation, who show a profound inability to communicate. The important contribution of this study is two-fold. First, it challenged the conventional wisdom that previously placed the blame of developmental disorders on the age of the mother. According to recent findings, the father’s age was crucial to the genetic risk of such disorders. Secondly, findings from this study are the first to quantify the effect of genetic mutations with each passing year. The research team found that children born of fathers who were 20 years of age had on average 25 random mutations. This figured increases by 2% ever year until it reaches a total of 65 random mutations in off-springs of 40-year-old fathers. Before older fathers decide to forgo fatherhood, the researchers caution that the overall risk to a man in his 40s is in the magnitude of 2% at most and other contributing biological factors are yet unknown. Although these findings may have some influence on parents’ reproductive decisions, experts say that the kind of random mutations observed in this study only account for 20%-30% of cases of autism and schizophrenia. The remaining 70% is probably due to a combination of genetic predisposition and environmental factors that influences gene expression. Instead of thinking in absolute terms and wondering whether you should have kids at the age of 20 when you are young and inexperienced, keep in mind that it’s all about the level of risk. The vast majority of these mutations have no consequences and many men in their 50s conceive and have healthy children!
Kong, A. et al., (2012). Rate of de novo mutations and the importance of father’s age to decrease risk. Nature, 488, 471-475.