HTT haplotype distributions in the Peruvian population. (a) The HD mutation in Peru occurs predominantly on the A1 haplotype (73%), of which nearly all are the Amerindian A1 variant haplotype. (b) Haplotypes of the HD mutation differ by geographic region of Peru. HD occurs most frequently on the A1 haplotype in Lima (including Cañete), North Coast, and the Northern Interior regions, but is more frequent on A2 in South Coast, and C1 in the Southern Interior. (c) Control HTT haplotypes in Mestizo Peruvians reflect indigenous ancestry with major European admixture and minor African contributions. (d) Control Amerindian HTT haplotypes reflect low genetic diversity in this subpopulation relative to Mestizo controls, and reveal the Amerindian A1 haplotype in the indigenous population of Peru.