A common JAK2 haplotype confers susceptibility to myeloproliferative neoplasms.

Genome-wide association studies have identified a number of new disease susceptibility loci that represent haplotypes defined by numerous SNPs. SNPs within a disease-associated haplotype are thought to influence either the expression of genes or the sequence of the proteins they encode. In a series of investigations of the JAK2 gene in myeloproliferative neoplasms, we uncovered a new property of haplotypes that can explain their disease association. We observed a nonrandom distribution of the somatic JAK2(V617F) oncogenic mutation between two parental alleles of the JAK2 gene. We identified a haplotype that preferentially acquires JAK2(V617F) and confers susceptibility to myeloproliferative neoplasms. One interpretation of our results is that a certain combination of SNPs may render haplotypes differentially susceptible to somatic mutagenesis. Thus, disease susceptibility loci may harbor somatic mutations that have a role in disease pathogenesis.