The following is an excerpt.
Scientists at USC have unlocked the mystery of why new cases of the genetic disease Noonan Syndrome are so common: a mutation that causes the disease disproportionately increases a normal father’s production of sperm carrying the disease trait.
When this Noonan syndrome mutation arises in a normal sperm stem cell it makes that cell more likely to reproduce itself than stem cells lacking the mutation. The father then is more likely to have an affected child because more mutant stem cells result in more mutant sperm. The longer the man waits to have children the greater the chance of having a child with Noonan syndrome.
Read the full story here: Common Genetic Disease Linked To Father’s Age