Many rare disorders, like sickle cell anemia, are caused by gene mutation. Yet, until now, the underlying genetic cause of more common conditions – for example, rheumatoid arthritis – has eluded scientists for years. New research from Case Western Reserve University School of Medicine finds that six common diseases arise from DNA changes located outside genes. The study from the laboratory of Peter Scacheri, Ph.D., shows that multiple DNA changes, or variants, work in concert to affect genes, leading to autoimmune diseases including rheumatoid arthritis. Further, for each disease, multiple different genes are manipulated by several small differences in DNA. The study is entitled, “Combinatorial Effects of Multiple Enhancer Variants in Linkage Disequilibrium Dictate Levels of Gene Expression to Confer Susceptibility to Common Traits.” In the study, the authors present evidence that for six common autoimmune disorders (rheumatoid arthritis, Crohn’s disease, celiac disease, multiple sclerosis, lupus, and ulcerative colitis) genome-wide associations arise from multiple polymorphisms in linkage disequilibrium that map to clusters of enhancer elements active in the same cell type. The authors say that this finding suggests a “multiple enhancer variant” hypothesis for common traits, whereby several variants in linkage disequilibrium impact multiple enhancers and cooperatively affect gene expression. They go on to show that multiple enhancer variants within a given locus typically target the same gene. The authors conclude that the “multiple enhancer variant” hypothesis offers a new paradigm by which non-coding variants can confer susceptibility to common traits. The research was published online on November 6, 2013 in Genome Research.
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