Low Serotonin Levels May Be Key to SIDS
Study Shows Link Between Sudden Infant Death Syndrome and Deficiency of Hormone Serotonin
WebMD News Archive
Explanations for SIDS
SIDS research is a ''controversial area," Kinney says. Many experts look to
the "triple risk" model to explain it, believing that SIDS results from an
underlying vulnerability, a critical developmental period, and an outside
''The real risk period is the first six months," Kinney says of the critical
period in which most deaths occur.
But experts disagree on what the vulnerability is. Kinney's research
suggests low levels of the neurotransmitter serotonin, and probably other brain
chemicals yet to be identified, are what make infants vulnerable. Other experts
suspect other vulnerabilities, such as infections.
Yet others say SIDS is due simply to suffocation, she says. "We say, yes,
some babies will die if they are severely asphyxiated," Kinney tells WebMD. But
she adds, "what we are saying is in the majority of cases, the babies have an
underlying defect that puts them at risk that makes them unable to respond to a
stressor, such as having their face compressed [while sleeping on the stomach
or becoming tangled in soft bedding]."
In previous research, Kinney and her colleagues found defects in the
serotonin system of SIDS babies, including defects in the serotonin receptors,
which are crucial for serotonin to work.
''But we never knew if there was too little or too much serotonin," she
says. "In this study, we actually measured the levels of serotonin and the
enzyme that makes serotonin."
Measuring Serotonin Levels
Kinney and colleagues evaluated serotonin and tryptophan hydroxylase (TPH2),
the enzyme that helps make serotonin, in 35 infants who died from SIDS.
They compared these measurements with those from two groups -- five infants
who died suddenly for whom a cause of death was established and five infants
who died while hospitalized for having insufficient oxygen to the tissues.
They retrieved tissue samples from the autopsies to measure the enzyme and
They found that:
- Serotonin levels were 26% lower in the SIDS babies than in the infants
who died suddenly with a known cause of death, and the enzyme levels were 22%
lower. The serotonin and enzyme levels were also lower in the SIDS babies than
in the group of hospitalized infants.
- Levels of binding to the serotonin receptors were also lower in the SIDS
Finding the deficiency in serotonin levels isn't the whole story, Kinney
says. "We think there are probably several neurotransmitter systems involved in