A new study has found that older fathers are more likely to pass along new genetic mutations to their children. It has been previously observed that children of older fathers are at increased risk for autism, schizophrenia and new single gene disorders such as achondroplasia, a type of dwarfism, and Apert syndrome.
The study “ Rate of de novo mutations and the importance of father’s age to disease risk” was published in the journal Nature on August 23, 2012. The authors studied the entire genome of 78 parent-child trios in families where the parents had no signs of a mental disorder gave birth to a child that developed either autism spectrum disorder or schizophrenia.
The results of this study demonstrate that nearly all of the new gene mutations detected in children were from mutations in the father’s sperm. For each year increase in the father’s age at conception, the number of new mutations increases by about two per year. The research team observed a child born to a 20-year old father had 25 random mutations that were paternal in origin. By age 40, the number had increased to 65. The great majority of the observed mutations will likely have no consequences. In comparison, the average number of mutations on the mother’s side was 15, regardless of her age.
Mutations such as seen in this study may account for up to 15-30% of autism cases and perhaps may also contribute to the development of schizophrenia. It will be interesting to see if other populations studied show similar findings.
Keep in mind, according to the CDC, that 1 in 33 children are born in the United States with a birth defect. With increasing maternal age, there is the known increase in chromosomal abnormalities such as Down’s syndrome. As an example, a 40 year-old woman has a 1 in 66 (1.5%) chance of delivering a live born child with a chromosomal abnormality.
This study is an important addition to our knowledge on the risks of delaying fatherhood. It is important to consider this information in light of many parents delaying childbearing. The authors report that the average of a new father in Iceland is 33. A similar pattern has been reported in other Western countries. In the United States, the age of fathers 40 and older has increased by over 30% since 1980.
Clearly, the causes of autism are multiple and complex. A single gene is probably not the sole cause of autism. Environmental and Maternal factors must be taken in account. The father’s age must be considered as one of the established risk factors. It has been estimated that at age 40, a man has a 6-fold increase in the likelihood of a child developing an autism spectrum disorder as compared to a 20 year-old
While autism and other new single gene conditions are seen in an increasing frequency in the offspring of older fathers, we must keep in mind that the vast majority of children born to older fathers are healthy.
It appears that men also have a biological clock!