In Nature a group of researchers from Denmark and Iceland report the results of their studies of mutation rates of Icelandic parent-child groups. They found that the level of new mutations, called a “de novo mutations,” in their samples when father’s average age was 29.7 was 1.20?X?10?8 per nucleotide per generation, but that number increases by two every year. In round numbers one might estimate that at about 20 years of age a father’s single sperm cell could carry 25 new spontaneous mutations, but at 40 years of age it might carry more than 65.
Not all the mutations would necessarily have ill effects; many are neutral, but those that affect brain structure and function would be particularly important. Of course effects on the brain would fit with problems such as autism and schizophrenia. Dr. Kari Steffansson, one of the lead scientists for the research, says that he is “absolutely convinced” that better diagnostic identification is responsible for increases in the observed rates of Autism, but he also thinks that trends toward later fathering of children is contributing to those observed increases, too.
As Professor Alexey Kondrashov, who is in the Department of Ecology and Evolutionary Biology and the Life Sciences Institute at the University of Michigan, wrote in an editorial that accompanies the study, it is “reasonable to assume that the ongoing increase in the incidence and prevalence of autism in many human populations could be due, at least in part, to the accumulation of mutations resulting from relaxed selection and a higher average paternal age—and not only to better recognition of cases.”
Listen to Dr. Kari Steffansson, one of the lead scientists discuss the study’s results in a podcast. It’s the first segment in Nature’s regular free audio show.
Kong, A., Frigge, M. L., Masson, G., Besenbacher, S., Sulem, P., Magnusson, G., … & Stefansson, K. (2012). Rate of de novo mutations and the importance of father’s age to disease risk. Nature, 488, 471-475. doi:10.1038/nature11396
Regular readers will recognize that these topics—de novo mutations, autism, and schizophrenia—have been discussed frequently on EBD Blog previously. Indeed, in 2007 Leslie Feldman compiled links on the topic of paternal age and autism and we created a document that is available as “Fathers’ Age as Contributor to Risk for Autism.” It’s cleverly hidden under the documents tab at the top of the page.