The genome-wide association study (GWAS) identified multiple gene variants not previously reported for these diseases, in addition to evaluating genes previously discovered to be associated with one, two or all three diseases. The study team found overlaps among gene variants that conferred risk for both T1D and IBD. They also found four variants impacting the genes PTPN22, IL27, IL18RAP and IL10 that raised the risk of T1D while lowering the risk of Crohn's disease.

These opposing effects, said Hakonarson, could suggest a possible "genetic switch" on some biological pathways involved in both IBD and type 1 diabetes. "For these autoimmune disorders, the switch could be activated by specific infectious agents that trigger immune responses that are mediated by selective immunological pathways," he said. He noted that a pathogen could interact with a gene that raises the risk for type 1 diabetes at the same time it confers protection from Crohn's disease. "Infections cause a lot of adaptation within the immune system, and could be exerting selective pressure in driving genomes to evolve, where the resulting disease risk or protection is more of a bystander," Hakonarson added.

Hakonarson cautioned that the potential genetic switch is currently an interesting hypothesis, requiring further investigation. Even the four gene variants (single nucleotide polymorphisms, or SNPs) that seem to cause opposing effects for these diseases may be markers for yet unknown causative genes that act in the same direction. "We won't know the exact impact of these variants until we have more sequencing data," he concluded.

Source: Children's Hospital of Philadelphia