Answer from: Douglas Lester, PhD, MSc, BSc (Hons)
Mostly genes that affect fertility are often known as recessive genes. This means you generally need to have inherited two bad copies of a particular sperm or ovum gene before you experience infertility. Such mutations or variations are often present in both your mother’s and your father’s side of the family. But these family members will be unaffected as they possess one good and one bad copy of the gene, which is enough to have a normal fertility phenotype. It’s only if you have the two bad ones together, you get the bad phenotype. Occasionally, however, you might have one bad copy of the variant form of a gene that is present in several individuals from one side of the family, say from your mother’s side. Unfortunately, you might also have a bad copy of the same gene from the other parent, say your father, where no individuals have a family history of a bad gene. In Latin, this mutation is called the Novo or the New or Sporadic Mutation; it has just occurred in the father’s sperm. It is in the development of the father/mother sperm or the father/mother ovum. Early on, there’s been a mutation that’s not in any other cells of the parents. It just happened in the progenitor cells of the sperm or ovum. So this mutation is then passed on and is present in all the chromosomes of the infertile patient.
An example of this is the chromosome 15 deletion that I mentioned earlier that causes deafness and male infertility. In this case, some may inherit the deletion of one of his chromosome 15s through his unaffected mother. The other would be chromosome 15 can be shown not to be present in DNA extracted from his father’s blood or saliva, but why is he got two bad copies of chromosome 15. The only explanation is inheriting a bad chromosome 15 from the father is that there’s been a new, de novo mutation during the father’s sperm production. Unfortunately, they end up with two mutated chromosomes 15, despite this mutation not being found in any of the father’s relatives. Novo and new mutations are much more likely to occur in older fathers. The older the sperm-making cells, the more likely a new mutation will come to arise. You get many more genetic mutations, the older the father, maybe over 40,50, and 60.
Hereditary, sporadic and acquired mutations – how do they impact my fertility?
Inherited (hereditary or germline) mutations, as the name suggests, are inherited from our parents and we are born with them. They include mutations that cause, for example, cystic fibrosis, hemophilia, and sickle cell disease. Other types of mutations that can surface during a person’s life are called sporadic, spontaneous, or new mutations.