Because the risk is inherited and varies in this way, the SNP, located on chromsome 11, had never been linked to T2D even though it had been genotyped in large, traditional genome-wide association studies (GWAS). These do not distinguish between paternally and maternally inherited SNPs. But deCODE can track the parental origin of virtually any SNP in the genome of the tens of thousands of Icelandic participants in the company's gene discovery work. In this study, deCODE used its population-wide genealogy database and proprietary statistical tools to determine the parent of origin of a number of SNPs in some 40,000 Icelandic participants in the company's gene discovery programs. Some of these SNPs had previously been associated with different diseases and are located near "imprinted" genes - genes in which only the maternally or paternally inherited copy is "switched-on" to encode a protein. Five of these, one each in breast and skin cancer and three in T2D, showed that the parental origin of the variants affects the risk they confer.

The paper, "Parental origin of sequence variants associated with complex diseases," is published online at nature, and will appear in the December 17 print edition.