It was in the middle of the day. Kristin Marr had showered and just finished vacuuming. “I thought everything was great. He had just moved into the nursery. It just turned horrible. I checked on him and he was blue,” says Marr, who lost her son Colton in 1999. He was only 8 weeks and 2 days old. Still tearful after eight years, she says, “You can’t do anything. The hardest thing is trying to understand why.”

Marr, who is married with two other children, is now the chairman of the Spring for SIDS national fundraiser and SIDS Awareness Day (www.springforsids.org).

LuAnn Kolbe, a parent and teacher, finds it hard to believe that this happened to her family as well.

“He was healthy and big, over eight pounds at birth. When it happened, we just didn’t believe it.” Kolbe’s son died 18 years ago while he was sleeping at a babysitter’s house. “Sometimes it feels like it was just yesterday,” she says.

Possible Causes of SIDS

Families who have lost a child to SIDS know that it’s every parent’s worst nightmare—checking in to find that their baby is not sleeping, but has passed away.

Sudden Infant Death Syndrome (SIDS) is the leading cause of post-neonatal infant death in the United States. SIDS deaths do not occur because of something parents did or failed to do; it cannot be explained. Usually the child is found dead after being put to sleep. Most SIDS deaths occur when a baby is between the ages of 1 and 4 months of age. Sixty percent of SIDS victims are male, and forty percent are female.

Brain Abnormality Research Sheds Light

According to results of a 2006 study in the Journal of the American Medical Association, researchers with the U.S. National Institute of Child Health and Human Development found evidence that SIDS may be caused by brain stem abnormalities, specifically an imbalance in the way the brain uses serotonin. The study found that some of the babies who died had an abnormality in the serotonin system that controls such basic functions as “breathing, heart rate, blood pressure, body temperature and arousal. Researchers have hypothesized that abnormalities may make an infant vulnerable to life-threatening challenges during sleep such as high carbon dioxide and low oxygen levels or elevated body temperature.”

“This finding lends credence to the view that SIDS risk may greatly increase when an underlying predisposition combines with an environmental risk, such as sleeping face down, at a developmentally sensitive time in early life,” says Duane Alexander, M.D., director of the NIH’s National Institute of Child Health and Human Development.

Serotonin is one of the neurotransmitters that relay messages between nerve cells, regulating mood and vital functions such as breathing and blood pressure. Normal levels of serotonin are needed for a baby to breath normally after gasping. Researchers found significant differences in the brainstems of SIDS infants.

In future studies, the researchers plan to examine the role of other serotonin receptor subtypes in both lab animals and in SIDS cases. According to Chuck Milhalko of SIDS Network, they also plan to test selective serotonin reuptake inhibitors (SSRIs) in pregnant lab animals to see if the drugs have an effect on the fetal animals’ developing brainstems in regions that are affected in SIDS infants. Currently there is no testing available for serotonin abnormalities.

Genetic Defects

Recent discoveries at Mayo Clinic added two more cardiac genes to the list of potential causes, increasing the possibility that genetic defects of the heart may cause up to 15 percent of SIDS cases.

Some researchers think that MCADD, a metabolic disorder, may also be to blame. Medium Chain Acyl-CoA Dehydrogenase Deficiency (MCADD) is a rare hereditary disease caused by the lack of an enzyme required to convert fat to energy. Some researchers believe that SIDS babies may have a gene for long QT syndrome, a subtle electrical disturbance in the heart that causes very fast heart rates.

Events After Birth

Lack of oxygen, and excessive carbon dioxide levels may produce respiratory infections, causing breathing problems that can lead to SIDS if babies breathe exhaled air trapped in underlying bedding when sleeping on their stomachs.

What Does It Mean?

While these studies explore potential preconditions for SIDS, Dr. Thomas G. Keens, a physician with the Division of Pediatric Pulmonology at Children’s Hospital, is quick to point out that “it is probably not as simple as one abnormality in one physiological system. There is no way currently to predict which baby will die from SIDS ahead of time. It is more likely that small differences in infant vulnerabilities … all come together to cause a SIDS death.”

“Current understanding of SIDS suggests a triple-threat model in that SIDS occurs during a particularly vulnerable developmental stage of a child, that there is an environmental trigger such as bundling, sleeping on a stomach, secondhand smoke and there exists defects in serotonin receptors in the brain that results in the baby being unable to restart their breathing after a period of apnea,” says Raymond D. Pitetti, MD, an Assistant Professor of Pediatrics. “Certainly, arrhythmias, metabolic disease, child abuse and infection play a role as well,”

What Can Parents Do?

Currently, Keens says, “There is no testing that anyone can do that will predict if a baby will die from SIDS.”

While there are no specific tests to predict which babies may be vulnerable to SIDS, there is now a procedure called tandem mass spectrometry, which screens for several hundred metabolic disorders in one blood spot, including MCADD.

“Some people think that these [MCADD defects] may be causes of up to five percent of SIDS deaths. However, this number is not proven. So, assuming it is in the ballpark, such testing of all infants might be expected to reduce the SIDS rate by five percent. Note that back sleeping alone has reduced incidences of SIDS by two-thirds, or 67 percent. Therefore, it would be misleading to suggest that this is a test for SIDS. MCADD is one of the metabolic disorders tested for, not the only one,” says Keens.

Many states now include tandem mass spectrometry as part of their routine newborn screening procedures (but it is not offered in California at this time). Keens feel that “for those families who have had two or more SIDS, a SIDS and an apnea, or severe apneas not resolving as one would expect, metabolic screening is reasonable.”

Tandem mass spectrometry can be used to effectively screen newborns for more than 40 potentially life-threatening metabolic disorders. Certain cases of sudden unexplained death after infancy might be attributable to complications of unrecognized metabolic diseases.

If your family has a history of SIDS, doctors may wish to screen for the possibility of a genetic disorder in your baby.

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Michelle Donaghey is a freelance writer.