A study that investigated the genomes of thousands of Icelandic parents and children has concluded that older fathers pass on far more genetic mutations to children than mothers do. Researchers found that children inherit 4 times more mutations from their fathers than their mothers, and therefore suggests that rare childhood diseases are more often caused by men’s DNA. This is not to be confused with the genetic mutations that cause infertility, which are the most significant age-related factors affecting couples and are highly correlated with the female parent’s age.
Men pass on more mutations as they make sperm throughout their lifetime, and are therefore exposed to the possibility of these genetic mutations, unlike women who are born with all of their eggs. The process used to create sperm accumulates more and more faults over time – something that does not happen to eggs as damaged DNA does not affect them in the same way.
Increased research focus on paternal age is likely to lead to more revelations of the impact of older fatherhood – previous research has largely focused on maternal age, so women feel more societal pressure to have children before they reach the age of 35-40, when fertility dips dramatically.
Sperm from younger men is of a higher genetic quality, and the upper age limit for sperm donors is 40 years in the UK for this reason. While the majority of mutations will not affect the health and wellbeing of children, some of these mutations can cause conditions such as autism and schizophrenia, which are likely to rise as more and more couples have children later in life.
Dr Kari Stefansson of deCODE genetics, the company that carried out the study, stated that “An extraordinary large percentage of rare disease in children are rooted in mutations that are not found in their parents.” This study begins to explain where and why these mutations occur.