Researchers studied the brains of 27 infants. Nineteen died from SIDS, and eight died from other conditions. The team compared the level of various cytokines (a class of proteins involved in regulating the immune system) in the brains of each group. All 19 SIDS brains showed strong or moderate levels of interleukin-1 (a type of cytokine) in the same regions of the brain stem. Six of the non-SIDS brains had weak, negligible or no level of interleukin-1 in the same regions, and the other two had a moderate level.
"We detected a pattern of cytokine in the SIDS brain that could overturn a delicate balance in molecular interactions in vital brain centers," said study author Hazim Kadhim, MD, PhD, of Université Catholique de Louvain and Free University in Brussels, Belgium. "It seems that high levels of interleukin-1 could be a common denominator in SIDS."
Cytokines like interleukin-1 could be released in the body in response to various stimuli, under infectious or inflammatory conditions, and when there is a lack of oxygen. Cytokines are not always harmful. When cytokines interact with neurotransmitters (substances that send nerve impulses across the brain), the result could change vital functions like arousal responses in the central nervous system, according to Kadhim. These modified arousal responses could cause SIDS.
The ages in each group were not exactly matched in the study. The infants with SIDS ranged six weeks to 10 months in age. The non-SIDS infants ranged one day to 18 months.
An editorial in the same issue of Neurology says the study results are subject to criticism because there is no agreement on what is a suitable control group to compare with SIDS infants.
"Since the SIDS and control infants were not age-matched, it's difficult to say how normal developmental changes in cytokine levels impacted the results," said editorial author Bradley T. Thach, MD, of Washington University School of Medicine in St. Louis, Mo. "Another crucial question is what is the cause of elevated cytokines in SIDS?"
Cytokine levels can be checked by examining blood, cerebrospinal fluid and amniotic fluid, said Kadhim. He also said that no studies have yet correlated the levels of cytokines in the brain with those in peripheral blood in SIDS infants.
Some believe that a combination of three conditions is necessary for a SIDS death to occur. In this "triple-risk model," the infant must have a vulnerability like sleep apnea or low birth weight. A trivial stressor such as a mild respiratory infection or partial lack of oxygen is often present. Unexpected death can occur when these two risk factors hit an infant during a critical period of development - usually between three and eight months.
SIDS remains the leading cause of death in infants between one month and one year of age in developed countries. The exact cause of SIDS is unclear.
The study was supported by grants from the Free University of Brussels, Université Catholique de Louvain and the National Fund for Scientific Research in Belgium.
The American Academy of Neurology, an association of more than 18,000 neurologists and neuroscience professionals, is dedicated to improving patient care through education and research. A neurologist is a doctor with specialized training in diagnosing, treating and managing disorders of the brain and nervous system such as stroke, Alzheimer's disease, epilepsy, Parkinson's disease, autism and multiple sclerosis.
For more information about the American Academy of Neurology, visit its web site at www.aan.com.