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Last year an international team of researchers reported that older dads are much more likely to father a child with mental health issues and learning disabilities. Now it looks like teen dads may risk passing on genetic mutations, according to researchers at the University of Cambridge and the Institute for Forensic Genetics in Munster, Germany.

In the study of 24,000 parents and their children, researchers found that men 20 years-old or younger were six times more likely to pass on genetic mutations to their children than teen mothers. They also found that kids of teen dads had more mutations than those of older dads.

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Overall, the risk of teen dads fathering a baby with birth defects was low (2 percent), but still significant. "The mutation rate is high in teenagers. It goes lower in the young adults and then rises again after 35," lead researcher David Forster told NBC News.

What's going on? There may be something wrong with the sperm of younger men and boys," NBC reported. Forster believes the mutations start with germ cells—the precursors to sperm cells. While women are born with all the eggs they will ever carry, men continually produce new sperm throughout their lives. It’s possible that "the mutations arise in sperm precursor cells, which may not be made anew but which may exist from early childhood."

Yet another reason to encourage teens to practice safe sex.