High levels of immune protein in infant brain linked to SIDS

High levels of a protein called cytokine in the brains of infants could hold a clue to the cause of Sudden Infant Death Syndrome (SIDS), according to a study in Neurology, the scientific journal of the American Academy of Neurology.

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.

Finding a pattern
"We detected a pattern of cytokine in the SIDS brain that could overturn a delicate balance in molecular interactions in vital brain centers," says study author Hazim Kadhim, MD, PhD, of Universit� 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," says editorial author Bradley T. Thach, MD, of Washington University School of Medicine in St. Louis, Missouri. "Another crucial question is what is the cause of elevated cytokines in SIDS?"

Detection before baby is born?
Cytokine levels can be checked by examining blood, cerebrospinal fluid and amniotic fluid, says 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.