Sudden Infant Death Syndrome, or SIDS, has been a tragic and largely-unexplained medical mystery for years. But now German scientists might have found a genetic component to explain why it happens to little boys.

After DNA from 156 white German infants who died of SIDS was analyzed, researchers found many of the male children had a mutation of an enzyme called MAOA that could have impaired their ability to properly breathe, while the same was not true for the female SIDS babies.

They also discovered that infants who died when they were between 46 and 154 days old — when most of the SIDS deaths in the group occurred — were much more likely to carry MAOA mutations than kids who died when they were more than 5 months old.

Study author Dr. Michael Klintschar, director of the Institute for Legal Medicine at Medical University Hannover in Germany, told, “The reasons for these abnormalities are unclear, but some scientists believe that the genes inherited by the parents might be one of several factors.”

However, he noted that the findings, published online and in the March issue of Pediatrics, haven’t yet been replicated in other population samples, and that “the risk conveyed by this gene variant is relatively small compared to other factors, like sleeping position [or exposure to] smoking.”

More details about SIDS can be found at the U.S. National Library of Medicine.