One in 15 men likely have mutations in their sperm that could cause childhood diseases, research suggests.
Human cells accumulate mutations as we age. When this occurs in sperm or egg cells, the mutations may be passed down to future generations.
Using state-of-the-art tools, scientists from the University of California in San Diego sequenced multiple sperm samples, identifying potentially harmful mutations in 6.66% of the cells.
"These mutations contribute a substantial burden on human health", causing up to 15% of autism spectrum disorders, newborn heart disease cases and other "severe paediatric" conditions, the scientists have warned.
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Identifying men with these mutations may help ward off childhood disease, they added.
The accumulation of mutations throughout a person's life is known as mosaicism. This causes different cells within the same individual to have varying DNA sequences.
Mosaicism does not usually cause symptoms, however if abnormal cells outnumber the healthy ones, it may result in disease.
To better understand this process, the San Diego scientists used a new method of counting these mutations.
"We found each ejaculate from a man shows an average of 30 mutations," said study author Dr Xiaoxu Yang.
The mutations were exclusively in sperm cells, not saliva or blood, and were "stably present" across multiple ejaculations.
Mutations that may cause disease were estimated to affect one in 15 men.
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"We think these mutations contribute a substantial burden on human health, potentially causing 15% of ASD [autism spectrum disorder] cases, congenital [present from birth] heart disease and severe paediatric diseases," said co-author Dr Joseph Gleeson.
"We are hopeful by identifying men at risk, future cases of disease can be avoided."
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The children of older men were thought to be more at risk of autism spectrum disorder or birth defects. In the San Diego study, however, sperm mutations did not differ between the older and younger participants.
"Our earlier studies told us sperm mutations contribute to the cause of disorders, such as autism and epilepsy, but the implications in men without a family history of disease was completely unknown," said Dr Joseph Gleeson.
Surprised by the results – published in the journal Cell – co-author Dr Martin Breuss added: "The comparison between the old and young men showed few differences in mutations, telling us these mutations probably arose when the father was an embryo, where the mutations could reside undetected until the man has children".
The scientists hope future research will focus on how to identify the causes of these mutations and better understand the role of environmental exposure in their onset.
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