New research reveals a significant increase in disease-causing genetic mutations in sperm as men age. The major finding, published in Nature, is that this increase is not just due to random accumulation, but because a form of natural selection within the testes actually favors and promotes the multiplication of certain harmful DNA changes during sperm production.
The study, led by scientists from the Wellcome Sanger Institute and King's College London, mapped how these mutations accumulate across the entire sperm genome in men aged 24 to 75.
Key Findings on Age and Risk
Researchers used a highly accurate sequencing technology (NanoSeq) to analyze sperm from 81 healthy men.
- Mutation Rate Rises with Age: The proportion of sperm carrying disease-causing mutations rose from about 2 percent in men in their early 30s to between 3 and 5 percent in men aged 43 to 74.
- The Selection Advantage: The increase is driven by a hidden process where specific mutations gain a reproductive advantage, allowing the sperm cells that carry them to multiply faster than others.
- Targeted Genes: The study pinpointed 40 genes favored by this selection process, many of which are linked to serious inherited risks, including neurodevelopmental disorders and inherited cancers in children. This phenomenon affects far more genes than previously understood.
Complementary Study Confirms the Effect
A separate, complementary study also published in Nature investigated the phenomenon by analyzing DNA mutations already passed on to children (from over 54,000 parent-child trios).
- This analysis also identified more than 30 genes where mutations gave sperm cells a competitive edge, with many genes overlapping the set found directly in sperm.
- The study found that these selected mutations can increase the sperm mutation rate up to 500-fold, helping to explain why some rare genetic disorders appear even when parents do not carry the mutation in their own DNA.
Implications for Future Health
The findings challenge the common assumption that the male germline is well-protected from genetic changes.
- Dynamic Germline: "The male germline is a dynamic environment where natural selection can favor harmful mutations, sometimes with consequences for the next generation," said Dr. Raheleh Rahbari, senior author.
- Future Research: While the number of affected sperm rises with age, the actual impact on children's health outcomes requires more study, as many mutations may prevent fertilization or cause miscarriage.
- Personalized Risk: By revealing this hidden selection process, the research aims to refine reproductive risk assessments and provide a better understanding of how genetics, lifestyle, and environment interact across generations.
Disclaimer: This content is published only for health awareness and informational purposes. It's not a substitute for your professional medical advice. You must consult a doctor/healthcare professional regarding your specific health concerns.
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