Fathers Pass on Four Times as Many Genetic Mutations Than Mothers, Study Says

New data out reveals that fathers pass on significantly more genetic mutations that could be responsible for many rare childhood diseases.

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Children inherit at least four times as many genetic mutations from their fathers than from their mothers, according to new research published in Nature. The study found that men passed on one new mutation for every eight months of age, whereas women only passed on a new mutation for every three years of age. But don’t worry dads, it’s not all bad or all your fault.

“De novo or new mutations provide an important part of the substrate for evolution, launching a constant flow of new versions of the human genome into the environment,” Kari Stefansson, study co-author and CEO of deCODE (the Icelandic genetics company that led the research), said in a statement. “However, they are also believed to be responsible for the majority of cases of rare diseases of childhood.”

Past studies have linked older fathers to schizophrenia, autism, and other such mental disorders, as well as more genetic mutations. Part of the reason for this is because men produce a large amount of sperm in a lifetime, and the more they do, the more DNA is copied over and over again with a bigger margin of error, thus producing a build-up of mutations in sperm over the years. However, scientists weren’t clear on how this compared to mutations passed on by mothers, who produce fewer eggs comparatively.

For the current study, Stefansson and his team looked at the entire genomes of 14,000 Icelanders — then narrowed the dataset down to the DNA of 1,548 people and their parents, along with a subset of 225 that included data from at least one child, for analysis. They found that new genetic mutations for mothers increase .37 for every year of age, compared to fathers whose increased 1.51 for every year of age. To put it in perspective, a kid would inherit about 13 mutations from their mother and 53 from their father if their parents had them at 35 years old.

However, results revealed in 10 percent of the genome, the mothers’ de novo mutations were equal to fathers. Researchers suspect that this is likely due to a flawed repair in double-strand DNA breaks that has existed in the genome for a very long time.

“It seems that when a chromosome breaks in an egg, it can sometimes be repaired, avoiding a chromosomal catastrophe but leaving a scar of small mutations,” Martin Taylor, a geneticist at the University of Edinburgh who was not involved in the study, explained to The Guardian.  

It’s important to note that not all genetic mutations are bad. Many changes in the genome are a necessary part of human evolution, but sometimes they cause rare and serious genetic diseases in children, such as Tay-Sachs. The purpose of having a greater inventory of what these mutations are isn’t so scientists can blame mom or dad. It’s so they are better equipped to identify, prevent, and potentially treat rare genetic diseases in the future through experimental gene therapy and editing.

“Providing a comprehensive catalog of such mutations from across an entire population is therefore not just scientifically interesting but also an important contribution to improving rare disease diagnostics,” Stefansson says.

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