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Gene Linked to Some SIDS Deaths

Identifying specific disorder explains the unexplainable

MONDAY, July 19, 2004 (HealthDayNews) -- Sudden infant death syndrome (SIDS) claims the lives of almost 3,000 infants each year in the United States, but what it is and why it happens is not known.

Now a new study sheds light on one cause.

Scientists have found a gene responsible for one type of SIDS, which they called sudden infant death with dysgenesis of testes, or SIDDT.

Babies who are born with this disorder seem normal, but die suddenly from cardiac and respiratory failure before their first birthday, according to the report.

"We have identified a gene that, when broken, causes kids to die in their infancy," said lead researcher Dietrich A. Stephan, director of the neurogenomics program at the Translational Genomics Research Institute in Phoenix.

This accounts for only one subclass of SIDS, Stephan stressed. The goal remains to find all the other causes.

"SIDS is a generic term that is used by doctors to say, 'We don't know what killed this baby,'" Stephan said. "It's not a diagnosis. It's more people throwing their hands up and not understanding it."

Several factors can cause SIDS, Stephan explained. These include accidents in the crib and genetic disorders.

Stephan and his colleagues identified patients with SIDDT in an Old Order Amish community in central Pennsylvania. SIDDT had taken the lives of 21 infants from nine families over two generations, according to the report in this week's issue of the Proceeding of the National Academy of Sciences.

All these infants died before one year from sudden cardiac and respiratory arrest. Though many of these infants were tested at major medical centers, they appeared to be normal.

To the researchers, this cluster of similar deaths suggested the cause was genetic.

Stephan's team studied DNA from four of these infants and their parents, brothers and sisters, and other family members. They found a gene called TSPYL, which is found in the brain stem and in testes, seems to be responsible for SIDDT.

This gene is involved in developing the brain's ability to manage breathing and heart rate. "If this gene is broken, that part of the brain doesn't develop correctly, and the babies have trouble breathing and regulating their heart," Stephan said.

According to Stephan, all the infants had two abnormal copies of the TSPYL gene, and all parents were carriers of this abnormal gene. "If one broken copy of the gene from Mom and one broken copy from Dad come together in a kid, that kid will die with 100 percent certainty," he said.

This genetic disorder appears to be common among Amish families, affecting almost 50 percent of the population. However, it is unclear how common it is in the general population. Finding this out is the next step in the research, Stephan said.

Stephan believes that finding out how common this genetic disorder is will account for a significant percentage of all SIDS cases.

"At some point, we are going to have the ability to test families that have had a sudden infant death in their family history and counsel them, so this doesn't happen in their family," Stephan said.

Moreover, the researchers hope to find treatments that will prevent the affected infants from dying. "This is pretty exciting," he said. "It starts to give families and doctors the ability to say, 'We really know what happened to your baby.'"

Stephan believes that other genetic disorders are also responsible for SIDS.

"One of our hopes is that we can get rid of the term SIDS, because it doesn't mean anything," Stephan said. "By identifying the real causes, you will have real names for real disorders."

"These are very exciting findings," said SIDS expert Dr. Debra E. Weese-Mayer, a professor of pediatrics and director of pediatric respiratory medicine at Rush University Medical Center.

"My research team has been studying the genetics that might predispose an infant to dying from SIDS," Weese-Mayer said. "This has been a slow concept to catch on despite very important findings. Hopefully, this paper will ignite the SIDS investigative network to accelerate the study of the genetic basis for SIDS."

Weese-Mayer believes a significant proportion of infants who have a genetic predisposition to SIDS, combined with environmental factors such as sleeping on the stomach, cigarette smoking, soft bedding and overheating, will account for many SIDS deaths.

"Just because the number of SIDS cases has declined with the aggressive Back to Sleep campaign does not mean that we are done with SIDS," Weese-Mayer said. "In reality, we are just beginning to get to the essence of SIDS."

More information

The National Institute of Child Health and Human Development has more about SIDS.

SOURCES: Dietrich A. Stephan, Ph.D., director and senior investigator, Neurogenomics Division Program, Translational Genomics Research Institute, Phoenix; Debra E. Weese-Mayer, M.D., professor, pediatrics, and director, pediatric respiratory medicine, Rush University Medical Center, Chicago; July 19-23, 2004, Proceedings of the National Academy of Sciences
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