Older Dads


The study by DeCODE in Iceland shows that each year a man delays fatherhood he increases the number of new genetic mutations that he passes on to his children. These “de novo” mutations are not ones that the father was born with, and therefore unrelated to any previous family history or condition. They occur spontaneously in the father’s sperm cells.

Using the data from the study, 23andMe’s Emily Chang lead the team that  created a simple tool that uses a man’s age to calculate the number of mutations he might pass on to his children.

So what does the number mean? The implication from the study is that the longer a man waits the more he increases the chances his child might develop certain kinds of conditions, such as autism. Yet while the risk may increase, it is still very low.

Also, keep in mind that despite the name, mutations are not necessarily bad. In fact, these different spellings within a person’s genetic code are largely benign while some may even be beneficial and lead to long term genetic diversity among people. Science writer Alok Jha pointed out in a piece in the Guardian that a single mutation in the APP gene actually protects against Alzheimer’s disease and helps people live longer. At the same time, some preliminary studies suggest that the more de novo mutations passed onto a child the higher the risk that child could develop certain types of conditions, such as autism and schizophrenia.

Or as lead author Kári Stefánsson, deCODE’s chief executive, told Ewen Callaway at Nature:

“The older we are as fathers, the more likely we will pass on our mutations. The more mutations we pass on, the more likely that one of them is going to be deleterious.”

For women, who pass on other risks to their children with age, the number of de novo mutations a mom passes on to a child is constant at about 14. The number of new mutations a father passes to a child goes up by two each year, so that a 50-year-old new father might pass on about 65 new mutations to his child, while a father half his age would pass on about 35 mutations. The reason the number of de novo mutations women and men pass on to their children is so different is because women are born with all their eggs, while men produce sperm throughout their lifetime, offering more opportunities for mutations to occur.

This doesn’t necessarily mean that men should start having kids or having their sperm frozen right out of college, but it does add more information for prospective fathers to consider. It also gives us a little more understanding about complex conditions like autism.

Past Autism Posts:
Autism Study Reveals No Genetic Associations
SNPwatch: We Care a Lot
SNPwatch: Genetic Variation Linked to Autism Risk In Boys


  • Tom

    I would like to know more in this area, such as do the mutations occur in a limited number of genes or is any gene fair game? Are certain genes more likely to have a mutation. Let’s say you have no mutations passed to a child and then you get 65 mutations will that cause a DNA test to show that you are unrelated to the child on STR, if you waited to test for 20 years. Basically a more detailed article as to what is known as of now and what may be suspected and trying to be discovered. I have been trying to find articles about this and have been stumped due to either the lack of information or work done in this area or I have just not found the magic Google or Yahoo search term to reveal the man behind the curtain.


  • Natalie

    @Tom – depends on the mechanism of mutation. As far as I know the study in question did not uncover the mechanisms leading to greater degrees of de novo mutations passed down from fathers. If the mutations are occuring through “random” accidents during replication, then any part of the genome is fair game and there is no preferred place. However, if the mechanism is not random (a repeat duplication, erroneous recombination, etc.) then certain regions may be more error-prone than others because of their chemical or informational composition.

  • Marla Jones

    Hello , this is a fascinating topic. My dad was 39 when I was concieved 50 years ago . My maternal grandfather was 61 when my mom was concieved in 1929. I want to keep up with this study!!!!!

  • Aaron

    I instinctualy feel it’s beneficial to have children at an older age because of the NOVA episode I saw on epigenes. I feel that we evolve during our lifetime and if we can survive more life throws at us and build an immunity to it we can pass that onto our children. While I’m sure there is a negative side, I think there is a strong positive side to this.

  • Jungle Boi

    I’m so confused by this article. A “de nova” – literally “from the start” are mutations that are not passed on from mother or father. Also confusing is that the last sentence and first post seem to contradict. Here they are:


    Past Autism Posts:
    Autism Study Reveals No Genetic Associations

    • ScottH

      You are correct. These are not mutations that the father or mother had and passed onto the child but mutations that occurred for the first time in one family member as a result of a mutation in a germ cell (egg or sperm) of one of the parents or in the fertilized egg itself.

  • Jungle Boi

    de novo*

  • John

    Why *not* freeze sperm right after college though? Are there any downsides?

  • LMar

    My father was 44 I believe.

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