Solving SIDS: The Serotonin Connection

A new study found low levels of serotonin in the brain tissue of infants who died from SIDS. The study suggests that a brain defect may cause some babies to be more vulnerable to sudden death while they sleep.

The results were published today in JAMA.



The autopsy analysis involved 35 infants who died from SIDS. They were compared with five infants who died from known causes.

Researchers examined small samples of tissue from the medulla. This is a region at the base of the brain. It regulates basic functions such as body temperature, breathing, blood pressure and heart rate.

Results show that serotonin levels were 26 percent lower in SIDS cases than in controls. Serotonin is a brain chemical that helps regulate mood. It also plays a role in regulating vital functions like breathing and blood pressure.

Measurements of “tryptophan hydroxylase” also were 22 percent lower in SIDS infants. This is an enzyme that is needed to make serotonin.

The authors suspect that this defect may hinder an infant’s capacity to respond to breathing challenges. As a result the child may inhale carbon dioxide that was exhaled while sleeping face down.

"Our research suggests that sleep unmasks the brain defect," senior author Dr. Hannah C. Kinney said in an NIH news release. "When the infant is breathing in the face-down position, he or she may not get enough oxygen. An infant with a normal brainstem would turn his or her head and wake up in response. But a baby with an intrinsic abnormality is unable to respond to the stressor."

Kinney hopes that a test will be developed to detect the abnormality. Steps could be taken to protect the infants who are most vulnerable.

She also said parents should continue to follow the Back to Sleep tips for safe infant sleep.

"Until 12 months of age, babies should sleep on their backs in a crib with a firm mattress, and without toys, soft pillows, excessive blanketing or excessive clothing," she told AFP.

An earlier study led by Kinney involved 31 infants who died of SIDS. The brainstems from SIDS infants contained more neurons that make and use serotonin. This suggested that the brain was compensating for low levels of serotonin.

Read more about sleep and infants and SIDS.