Over time, all human cells accumulate mutations, resulting in what is called mosaicism, a condition in which different cells from the same person have different DNA sequences. Mosaicism occurs in all humans, but mostly goes unnoticed .
When mosaicism occurs in human sperm, the mutations can affect both the man and subsequent generations. A new study published in Cell describes a new method to observe and count these mutations, and use this data to predict the likely impact of these mutations on future children .
1 in 15
The study reports that 1 in 15 men is likely to carry mutations in their sperm that could negatively affect their offspring. Previous research suggested that older men are at higher risk for certain diseases in their sons, such as autism spectrum disorder (ASD) and some forms of birth defects. In the latest study, researchers compared sperm from older men to younger men to determine differences in mutations .
They found that the detectable mutations did not differ in number, suggesting that these mutations create a stable risk of disease in the offspring. The findings also indicated that age-associated mutations are more likely to arise in single sperm cells, occurring below current levels of detection. Be the co-author Xiaoxu Yang:
We found that each ejaculation from a man shows an average of 30 mutations. Almost all of these were found in serial samples over a period of six to 12 months, while most of the mutations were completely absent in a saliva or blood sample.
Future research, the authors said, will focus on identifying the causes of the mutations that arise in older men and the environmental exposures that could explain the observed increases in mutations . The team is recruiting families where a child has a disease due to a new mutation and where the father can donate a sperm sample to look for evidence of the mutation.