The results suggest an association between SIDS and the 5-HTT gene. "There was a significant difference in genotype distribution and an increased frequency of the L allele in SIDS cases versus ethnicity/gender matched controls with no family history of SIDS or autonomic dysfunction," the authors report. "Furthermore, there were significantly fewer SIDS cases versus controls with no long allele (S/S genotype) in the entire cohort and within the Caucasian subgroup; and significantly more SIDS cases versus controls with no short allele (L/L genotype) in the entire cohort."
The researchers also found that genotype frequency distributions and allele frequency distributions for 5-HTT were significantly different when evaluated across all ethnic groups. Despite ethnic variations, however, SIDS cases were more likely than controls to have the long allele in the Japanese, Caucasian, and African American study samples.
The study's results are compelling, though limited by the research design that included only confirmed anonymous SIDS cases from the NIH-supported University of Maryland Brain Bank, according to Dr. Weese-Mayer. Further studies should encompass larger numbers and more ethnicities and also include the 5-HTT intron 2 VTNR which influences gene expression. Likewise, Dr. Weese-Mayer et al pointed out that "recognizing the strong relationship between tobacco exposure (prenatal and postnatal) and SIDS risk, future studies of genetic polymorphisms must also include detailed smoking history to clarify the role of gene-environment interaction."
"If a larger data set reflects observations similar to those in this report," the authors conclude, "the serotonergic system will represent a key area for further investigation into the causal basis for SIDS, with the goal of identifying genetic risk factors that will aide in recognizing at-risk individuals who require specialized intervention strategies and in counseling families as to the risk of
Contact: John M. Pontarelli
Rush University Medical Center