AFTER struggling for years to ­explain why some apparently healthy babies die suddenly in their sleep, a study ­published recently singles out ­serotonin deficiency as a key culprit in sudden infant death syndrome (SIDS) or cot death.

Researchers at the Children’s Hospital in Boston found that infants who died of cot death, which is the leading cause of death in babies under the age of one in the United States, had significantly lower levels of the ­neurotransmitter  serotonin and the enzyme that helps make it in their brainstems.

SIDS babies also had fewer ­serotonin receptors in the brainstem, another  indication that there was a problem with the babies’ systems, ­according to the  study, which was published in the Journal of the American Medical Association (Jama).

Brainstem serotonin controls ­involuntary functions such as heart rate,  blood pressure, body ­temperature and breathing.

The researchers who conducted the study believe that SIDS claims babies’  lives because the serotonin-deficient brainstem, which works with no back-up during sleep, fails to spring into action to alert the infant when it is faced with a life-threatening challenge while asleep.

“When the baby is awake, the brainstem works together with other systems in the forebrain to control functions like heart rate and  ­breathing,” David Paterson, one of the lead authors of the study, told AFP.

“However, when the baby is asleep, the higher functions in the brain switch  off, so the brainstem system itself is solely responsible for controlling all  these functions,” he said.

If the infant has a serotonin ­deficiency, and if there are other SIDS  risk-factors such as the baby ­sleeping on its stomach and rebreathing its own breath, which contains more carbon dioxide, the serotonin system in the brainstem could fail to detect a ­problem and ‘tell’ the baby to take action, Paterson explained.

“If the serotonin brainstem system is not working properly, the baby might not respond to this challenge and die.”

The findings of the small study, which looked at tissue from 35 babies who died of SIDS, marked a step forward in the fight to end cot death, which has stumped doctors for ­decades.

Earlier studies which found that the risk of cot death increased when a baby is laid on its stomach to sleep had sparked campaigns around the world to get parents to lay their little ones in their cribs for the night on their backs or sides.

The campaigns initially met with success, but then the overall SIDS rate  levelled off and has stayed steady for years.

Following this latest study, the researchers say the next step would be to  devise a test to identify infants with a serotonin brainstem defect and develop treatments to correct serotonin deficiency.

But they stressed that while the study provides strong evidence for a  biological cause of SIDS, it also shows that other factors, such as  stomach-sleeping, can aggravate the risk of cot death.

Of the 35 SIDS infants in the study, 95% died with at least one risk factor and 88% died with at
least two.

Until scientists have come up with a test and remedy for serotonin ­brainstem deficiency, parents can do their part to reduce the danger of their baby dying suddenly in its sleep by removing SIDS risk factors from the infant’s ­environment, said ­neuropathologist Hannah Kinney, who led the study.

“During pregnancy, there is no safe level of alcohol a mother can drink and no safe level of smoking.

“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 said. – AFP