Sudden infant death syndrome, or SIDS, is the leading cause of death in babies from one to 12 months, killing about 2,500 infants in the United States each year. Three decades of research have found factors that increase the risk of SIDS–such as letting babies sleep on their stomachs–but no definitive answers as to what causes the condition. Recently, studies have pointed to genetic and brain abnormalities that predispose an infant to SIDS. In an isolated Amish community in southern Pennsylvania, nine families lost 21 babies in two generations to the mysterious condition and scientists from all over the country investigated to try to find a genetic link to the deaths.

What the researchers wanted to know: Why did so many seemingly healthy babies in one community die from unexplained causes?

What they did: The researchers, led by neurogeneticist Stephen Dietrich of the Translational Genomics Research Institute in Phoenix, analyzed DNA from four of the infants who died in southern Pennsylvania in the past several years, as well as DNA from their families. They looked for variations in specific chromosomes and in the genes that make up those chromosomes. When they found an abnormal gene in the affected infants, the researchers looked up the function of that gene and searched for any related symptoms the infants had before they died.

What they found: The four infants studied all had two abnormal copies of a gene called TSPYL, which regulates sexual differentiation, testicular development, and brain function. Their parents each had one abnormal TSPYL gene, so they were carriers of the condition, but, because the gene is recessive, the condition appears only in children who got two malformed copies of the gene from their parents. The two boys who died suddenly had underdeveloped testes or ambiguous genitalia, but the girls had no external sexual signs. Autopsy reports from the other 17 babies who died also showed that some of those babies had subtle, and often externally invisible, reproductive abnormalities. The researchers named this new variation of SIDS sudden infant death with dysgenesis of testes (SIDDT). Dysgenesis means disabled development and usually refers to an organ.

What it means to you: While the researchers think this genetic abnormality is likely rare, and possibly confined to several Amish populations, their research strongly suggests faulty genes may be responsible for other SIDS deaths. It also is one of the first subclassifications of SIDS, which is still a catchall term for unexplained infant deaths, and could lead to real diagnoses for the syndrome. Other studies have pointed to genetic variations that predisposed babies to SIDS, but this is the first study to directly link an abnormality to a type of SIDS and to separate that type out from other cases of sudden infant death.

Caveats: The population studied was very small and isolated, so it is not likely that this specific genetic variation appears often in the larger population. The study is better used as a model for how future genetic research could illuminate the causes of SIDS.

Find out more: The National SIDS/Infant Death Resource Center has facts about the condition, risk factors, and links to other websites and the American SIDS Institute also has a good amount of information. First candle, has information for expectant and new parents on how to prevent SIDS and support for families who have lost a baby. And, though the Amish won't be looking at it, there's a website with lots of good information about the Amish, including why they do not use electricity.

Read the article: Puffenberger, E.G. et al. "Mapping of Sudden Infant Death With Dysgenesis of the Testes Syndrome y a SNP Genome Scan and Identification of TSPYL Loss of Function." Proceedings of the National Academy of Sciences. August 10, 2004, Vol. 101, No. 32, pp. 11689-11694.

Article online: http://www.pnas.org