Rare missense variants within a single gene form yin yang haplotypes.

Yin yang haplotype pairs differ at every SNP. They would not be accounted for by population models that incorporate sequential mutation, with or without recombination. Previous reports have claimed that there is a tendency for common SNPs to form yin yang haplotypes more often than would be expected by sequential mutation or by a random sample of all possible haplotypic arrangements of alleles. In the course of analysing next-generation sequencing data, instances of yin yang haplotypes being formed by very rare variants within a single gene were observed. As an example, this report describes a completely yin yang haplotype formed by eight rare missense variants in the ABCA13 gene. Of 1000 genome subjects, 21 have a copy of the alternate allele at all eight of these positions and a single subject is homozygous for all of them. None of the other 1070 subjects possesses any of the altetrnates. Thus, the eight alternate alleles are always found together and never occur separately. The existence of such yin yang haplotypes has important implications for statistical methods for analysing rare variants. Also, they may be of use for gaining a better understanding of the history of human populations.