Complex haplotypes of metabolizing GSTM1 gene deletion harbors signatures of a selective sweep in East Asian populations

Abstract

The deletion of the metabolizing Glutathione S-transferase Mu 1 (GSTM1) gene was previously associated with multiple cancers, metabolic and autoimmune disorders, as well as drug response. It is unusually common, with allele frequency reaching up to 75% in some human populations. Such high allele frequency of a derived allele with apparent impact on an otherwise conserved gene is a rare phenomenon. To investigate the evolutionary history of this locus, we analyzed 310 genomes using population genetics tools. Our analysis revealed a surprising lack of linkage disequilibrium between the deletion and the flanking single nucleotide variants in this locus, indicating gene conversion events. Tests that measure extended homozygosity and rapid change in allele frequency identified signatures of an incomplete soft-sweep in the locus. Using empirical approaches, we identified the Tanuki haplogroup, which carries the GSTM1 deletion and is found in approximately 70% of East Asian chromosomes. This haplogroup has rapidly increased its frequency in East Asian populations, contributing to a high population differentiation among continental human populations. We showed that extended homozygosity and population differentiation for this haplogroup is incompatible with simulated neutral expectations in East Asian populations. In parallel, we revealed that the Tanuki haplogroup is significantly associated with the expression levels of other GSTM genes. Collectively, our results suggest that the Tanuki haplogroup has likely undergone a soft sweep in East Asia with multiple functional consequences. Our study provides the necessary framework for further studies to elucidate the evolutionary reasons that maintain disease-susceptibility variants in the GSTM1 locus.\n\nLay summaryHere, we describe the evolutionary forces that shape the variation in a genomic region, which has been associated with bladder cancer, metabolic and autoimmune disorders and response to different drugs. Our results reveal a new genetic type common in Asian populations that may have important evolutionary and biomedical implications.