Research: Sudden Infant Death Syndrome

Ongoing research is being conducted to determine the cause for sudden infant death syndrome. Recent studies have revealed some possible leads.

Brain Abnormalities and SIDS

Some doctors theorize that SIDS babies may have a defect in the arcuate nucleus, which is the area of the brain that regulates blood pressure, breathing, and body temperature, along with sleeping and waking processes. More specifically, this defect appears to affect serotonin, a neurotransmitter that spreads messages between the brain and nerve cells. Researchers discovered that SIDS babies often had problems with the way serotonin functioned in their brains.

For example, if a baby without this defect breathes stale air while sleeping, an automatic reaction triggers the baby to move or to wake up and cry, increasing oxygen intake and adjusting the heart rate. But a baby born with this brain defect is not able to respond to the trigger because the message concerning the stale air is not being transmitted properly. This could result in SIDS.

This brain abnormality might work in a similar way when a baby is overheated. Normally, if a baby is too warm, he or she will wake up and move or cry. But in a baby who has this defect, the brain might not trigger that response, again possibly leading to SIDS.

Defects in other parts of the body may also be responsible for increasing SIDS risk. For example, some abnormalities may form if a fetus is exposed to a toxic substance, such as cigarette smoke. Also, fetuses of mothers who smoke during pregnancy may not receive the right amount of oxygen before birth, making the baby more sensitive to changes in oxygen levels after birth.

Dangers of Covers Over the Infant's Head

In June 2008, a team of researchers from New Zealand reported that covering the head (e.g., with blankets) might play a role in SIDS deaths. After reviewing SIDS cases in New Zealand and Germany, the researchers found that in 15.6 percent of New Zealand SIDS cases and 28.1 percent of German SIDS cases, the infants' heads were covered and sweaty before they died. This occurs more often in older infants than younger babies, corresponding to the infant's growing ability to move in the crib.

Bacterial Infections and SIDS

In May 2008, British researchers announced a possible connection between Staphylococcus aureus and Escherichia coli (E. coli) infections and SIDS. In this study, samples of bacteria were taken from 470 infants who had died before their first birthday and examined. Of the group, researchers discovered higher levels of bacteria present in babies whose deaths were unexplained and attributed to SIDS than in those whose deaths were attributed to causes that could be explained.

It was noted that around 8 to 10 weeks of age, a common age for SIDS occurrences, babies normally start to lose the antibodies they were born with, which were obtained through the placenta. Because infants in the study had not yet built up enough of their own antibodies, they might not have been able to fight off infection. It is important to note, however, that this connection is still considered a preliminary finding that needs further research. There is not enough evidence to say that bacterial infections can cause SIDS.

Inner Ear Abnormality and SIDS

In 2007, a connection between newborn hearing and SIDS was reported. In this study, newborn hearing test results of 31 infants who had died of SIDS were evaluated and it was determined that each baby had an abnormality in the right inner ear.

It may be possible that this inner ear abnormality is connected to the ability of the infant's body to adjust the respiratory system when carbon dioxide levels increase. Inner ear damage may occur during delivery, particularly if the mother is in labor for more than 16 hours. Usually, this type of injury heals by the time the baby is 6 months old; the age of 6 months is generally when the incidence of SIDS starts to decrease.

However, further research is needed to determine whether this inner ear abnormality can predict a higher risk for SIDS. Also, newborn hearing tests are not regulated worldwide, so a more reliable measure would be necessary to accurately predict risk.

Genetics and SIDS

In January 2007, researchers reported that approximately 10% of SIDS babies have a mutation in a heart gene that can cause deadly changes in heart rhythms (arrhythmias). Further research is necessary to determine whether widespread heart screenings for newborns is warranted and, if so, the best procedures to use.

A mutation in a heart protein was discovered in 2006. When this defect is present, it increases the risk for SIDS in African American babies 24 times. This genetic mutation causes an irregular heartbeat when oxygen levels have lowered.

In 2004, researchers in Lancaster County, Pennsylvania and Phoenix, Arizona reported the discovery of a mutated gene that had been passed down through two generations of nine Amish families. This gene mutation affects the body's ability to regulate breathing and heart rate. In this study, 21 babies in the families who had this mutation died of SIDS. Researchers are now studying the gene in non-Amish children to determine if the mutation is common in non-Amish populations.

Depression in Mothers and SIDS

In a study conducted in 2007, researchers reported that babies born to mothers who had experienced depression during the year before delivery were five times more likely to die of SIDS than babies whose mothers had no history of depression. However, more research is needed to determine if additional factors, such as low birth weight and premature birth are related to this link.

Air Quality and SIDS

A connection between pollution and SIDS in California was reported in 2006. By studying levels of carbon monoxide, nitrogen dioxide, ozone, and other air particles at different intervals before infant deaths, researchers concluded that exposure to high levels of pollution increased the risk for infant death before the age of 1 year.

The study also indicated a higher risk for premature infants and infants with low birth weight; however, it did not explore the roles of other factors, such as secondhand smoke and infant sleeping position. The study also noted the relationship between pollution and death from SIDS and other respiratory diseases, not SIDS alone.

Testosterone and SIDS

In 2006, researchers reported unusually high levels of testosterone in both male and female infants who had died of SIDS when compared to babies who had died of other causes. High testosterone levels can be linked to a decrease in ventilation among sleeping adults and ongoing studies are being conducted to determine if there is a cause and effect relationship between these levels and SIDS.

Other SIDS Research

According to the American SIDS Institute, "…most (60–70 percent) of the [SIDS] deaths are related to a subtle chronic abnormality, which occurs before birth. At this time, we do not know the specific pattern or nature of this chronic abnormality." The Institute plans to conduct extensive research to develop tests that will help doctors identify the abnormality at birth. In addition, researchers will conduct studies during pregnancy to help determine what prenatal factors might lead to this abnormality and how to prevent the abnormality from occurring.

Publication Review By: the Editorial Staff at

Published: 28 Aug 2008

Last Modified: 05 Mar 2015