A woman’s eggs decline in quality and quantity as she ages, at least in part because an important DNA repair pathway becomes impaired, according to a paper published today (February 13) in Science Translational Medicine.

The pathway, which includes proteins encoded by the well-known BRCA genes, is supposed to repair double-strand breaks in DNA. But as women get older, the study found, repair mechanisms lose efficiency and reproductive cells accumulate damaged genes and often commit suicide.

“I think we have found a general theory of reproductive aging,” said coauthor Kutluk Oktay, a fertility specialist at New York Medical College and the Institute for Reproductive Medicine and Fertility Preservation.

“They are tying together something that has been perplexing and vexing, which is what happens to women’s eggs as they age,” said David Keefe, a New York University Langone Medical Center fertility doctor who wrote a commentary on the paper.

While women are born with 1 million oocytes, only about 500 turn into full-fledged eggs over their lifetime. By the time women reach their early 50s, the remaining oocytes have almost completely degraded. Why the oocytes degrade so rapidly in comparison to other body tissues was a mystery.