Sperm Mutations That Can Cause Diseases Among Kids Identified

Throughout development, life, and the processes of aging, all human cells accumulate mutations, resulting in what is called mosaicism, a condition in which different cells in the same person have different DNA sequences or genetic makeup, Scott Lafee of the University of California-San Diego reported for Phys.org.

Photo Insert: 3d rendering of sperm cells

Mosaicism occurs in every human but is mostly unnoticeable. If abnormal cells begin to outnumber normal cells, however, diseases may result. When mosaicism occurs in human sperm or egg cells, the mutations can affect both man and woman with the mutation and subsequent generations.

In a study published in the journal Cell, researchers from the Rady Children's Institute of Genomic Medicine and University of California San Diego School of Medicine describe a new method for observing and counting these mutations and using this data to predict the likely impact of these mutations on future children.

Notably, they report that one in 15 men is likely to carry mutations in their sperm that could adversely affect their offspring. Previous research suggested that older men have a higher risk of certain diseases in their children, such as autism spectrum disorder (ASD) and some forms of birth defects. In the latest study, researchers compared sperm from older men with younger men to ascertain any differences in mutations.

They found that detectable mutations did not differ in number, suggesting these mutations create a stable risk of disease in offspring.

"We think that these mutations contribute a substantial burden on human health," said Dr. Joseph Gleeson, Rady Professor of Neuroscience at UC San Diego School of Medicine and director of neuroscience research at the Rady Children's Institute for Genomic Medicine, "potentially causing 15 percent of ASD cases, congenital heart disease and severe pediatric diseases. But we are hopeful that by identifying men at risk, future cases of disease can be avoided."

The findings also indicated that age-associated mutations appear most likely to arise in single sperm cells, which occur below current levels of detection.

"Our earlier studies told us that 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 Gleeson.

"We found that each ejaculate from a man shows an average of 30 mutations," said co-first author Xiaoxu Yang, Ph.D., a postdoctoral scholar in Gleeson's lab. "Almost all of these were found in serial sampling from a period of six to 12 months, whereas most of the mutations were completely absent from a saliva or blood sample."

The data, said Yang, indicates the mutations are restricted to sperm cells, and also validates their detection method.

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