While many mechanisms can lead to parental origin specific association with a phenotype, a priori sequence variants located close to imprinted genes are more likely to exhibit such behaviour. Through two sources, Luedi et al.3 and the Imprinted Gene Catalogue4, 5, we found forty eight genes known to be imprinted in humans (Supplementary Table 1). Selecting regions that fall within 500 kb of any of these genes (Build 36 of the Human Genome Assembly) amounts to approximately 1% of the genome. The 500 kb threshold was chosen because imprinted genes often occur in clusters and the imprinting status of genes close to known imprinted genes is often undetermined. It is also known that a sequence variant can directly affect the function of a gene located some distance away. Among the 298,069 SNPs we processed, 3840 fall within these selected regions.
