Epistasis Blog

From the Computational Genetics Laboratory at Dartmouth Medical School (www.epistasis.org)

Sunday, August 27, 2006

Epistatic interactions: how strong in disease and evolution?

A new paper to appear in Trends in Genetics looks like it might provide an interesting discussion about epistasis:

Azevedo L, Suriano G, van Asch B, Harding RM, Amorim A. Epistatic interactions: how strong in disease and evolution? Trends Genet. 2006 Aug 12

When the chimpanzee genome sequence was released, human deleterious alleles associated with simple mendelian diseases were observed as wild-type alleles in six genes (AIRE, MKKS, MLH1, MYOC, OTC and PRSS1). The absence of recognizable phenotypic effects in chimpanzee, contrary to the clinical effect observed in humans, is attributed to epistatic interactions (compensation) between potentially deleterious and compensatory alleles. In this report we investigate the possible evolutionary histories by which substitution of alternative variants in these six genes either ameliorates or avoids pathological consequences.

Monday, August 07, 2006

Multilocus interactions and preterm birth

A new study by Menon et al. published in the American Journal of Obstetrics and Gynecology used our open-source MDR software to detect a three-way interaction that was associated with preterm birth.

Menon R, Velez DR, Simhan H, Ryckman K, Jiang L, Thorsen P, Vogel I, Jacobsson B, Merialdi M, Williams SM, Fortunato SJ. Multilocus interactions at maternal tumor necrosis factor-alpha, tumor necrosis factor receptors, interleukin-6 and interleukin-6 receptor genes predict spontaneous preterm labor in European-American women. Am J Obstet Gynecol. 2006 Jun;194(6):1616-24. [PubMed]


OBJECTIVE: We hypothesize that genetic variations (single nucleotide polymorphisms-SNPs) in the tumor necrosis factor-alpha (TNF-alpha), TNF receptors (TNFRI and TNFRII), interleukin-6 (IL-6) and IL-6 receptor (IL-6R) genes predict high-risk status for spontaneous preterm birth (sPTB) in European-American women. In this study we examine the allelic and genotypic variations and the gene-gene interactions in the TNF-alpha, TNFRs, IL-6, and IL-6R genes in maternal DNA samples by using a case-control model. STUDY DESIGN: Maternal DNA from cases of sPTB after preterm labor (n = 101) and controls (normal term labor and delivery) (n = 321) were genotyped for SNPs in the TNF-alpha (6), TNFRI (6), TNFRII (7), IL-6 (5), and IL-6R (3) loci. SNPs were tested for both allele and genotype differences (cases vs controls) with the use of standard genetic epidemiologic methods. Multilocus interaction was assessed with multifactor dimensionality reduction analysis (MDR) to test all single and multilocus combinations for the ability to predict sPTB. RESULTS: Few significant allelic and genotypic associations were detected between cases and controls in maternal DNA. Single locus analysis documented independent association of SNPs at -7294 (allele and genotype) of TNFRI and 24660 (genotype) TNFRII loci with sPTB. MDR revealed a significant 3 locus model that includes SNPs -3448 of TNF-alpha, -7227 of IL-6, and 33314 of IL-6R. This interactive model allowed the successful prediction of pre- to low-risk genotypes is 3.50 (95% CI 2.52-4.87, P < .001). CONCLUSION: This is the first report to document a multilocus interaction in sPTB that predicts 65.2% of the cases in a European-American sample. Although putatively significant associations with sPTB were seen at a few single locus sites in TNFRI and TNFRII, they were not as predictive as the 3-locus model produced by MDR, suggesting the use of multilocus analyses in gene association studies of complex disease such as sPTB.