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When it comes to procreation, many genetic disorders are often attributed to the age of a woman. The common consensus is that the older the woman, the higher the risk of birth defect. A recently released study contradicts this belief. It shows that - with the exception of Down Syndrome - a father’s age plays a more active role in the gene mutations passed down to children.
Believe it or not, this study actually started in the 1930’s by a leader in the, then, up-and-coming field of genealogy, J.B.S. Haldane. During a study of haemophilia and hemophilia, Haldane noticed a peculiar and common pattern of inheritance for families with long histories of the blood disorder. He noticed that the blood disorder was passed down on the X chromosome from father to daughter, not on the X chromosome passed by the mother. He suspected that children would inherit more genetic mutations from the father rather than the mother, but since genetics was in its infancy in the 1930’s, Haldane had no way to prove this. Seventy something years later, geneticists have proved just that.
By looking farther into the passing of chromosomes, researchers were able to identify that fathers - especially those starting families later in life - pass down more mutations to children than mothers. While older moms still have the chance of passing along Down Syndrome to a child, older dads can pass along many more gene mutations through their sperm. The study shows that men who started their families in their 30’s, 40’s, and older have the ability to pass along twice as many, if not more, new gene mutations to their offspring. In fact, as the average age of fathers has risen from 28 in the 1980’s to 33 in 2011, so have the number of gene mutations. In the 1980’s there was an average of 60 mutations harbored by newly born children, while in 2011 there was an average of 70 new mutations. Not a huge jump, but when you consider that these mutations can cause Autism Spectrum Disorder and Schizophrenia, the jump is significant.
But why do these mutations occur? Haldane actually had the answer back in the 1930’s, though he had no way to prove it. He believed that since men continually develop sperm, they have a higher chance of creating more new mutations, more frequently. As a man ages, he will continue to develop sperm, but also as he ages, the sperm he develops will be able to mutate time and time again in varying ways. Some of these mutations may be completely harmless, while others pose significant health risks for their children.
The trend of waiting till later in life to start a family has been growing over the past decade, as many men and women are waiting until they are well into their 30’s to have their first child. While most are familiar with the risks of pregnancy post age 35 for ladies, there has never been a line drawn for men. Now, there is at least a general rule that men can follow to provide the healthiest genes for their offspring. In general, one can expect new gene mutations to occur at a doubled rate every 16 years. In theory, men who are in the age range of 48-64 will be 2 times more likely to pass along a serious gene mutation to a child than a man under the age of 32 years. It is speculated that the delay to start families may be impacting the escalation of diagnosed autism cases. However, at this time is not definite whether this particular situation is determining the number autism cases, or if wider and more accurate testing for autism is becoming more effective.
Sources:WebMD - http://children.webmd.com/news/20120822/fathers-age-linked-autism Forbes - http://www.forbes.com/sites/alicegwalton/2012/08/24/parental-age-especially-the-fathers-is-linked-to-genetic-mutations-in-the-child/ Nature International Weekly Journal of Science (where report was published) - http://www.nature.com/news/fathers-bequeath-more-mutations-as-they-age-1.11247