Common variants in the trichohyalin gene are associated with straight hair in Europeans

Abstract

Hair morphology is highly differentiated between populations and among people of European ancestry. Whereas hair morphology in East Asian populations has been studied extensively, relatively little is known about the genetics of this trait in Europeans. We performed a genome-wide association scan for hair morphology (straight, wavy, curly) in three Australian samples of European descent. All three samples showed evidence of association implicating the Trichohyalin gene (TCHH), which is expressed in the developing inner root sheath of the hair follicle, and explaining approximately 6% of variance (p=1.5x10(-31)). These variants are at their highest frequency in Northern Europeans, paralleling the distribution of the straight-hair EDAR variant in Asian populations.

Figure 1

Genome-wide Association Results (A) Manhattan plot showing the results for the genome-wide meta-analysis of hair morphology across three independent samples. SNPs with a p < 10⁻⁵ are highlighted in green. (B) Karyotype of chromosome 1 highlighting the 1q21 region. (C) Regional association and linkage disequilibrium plot for the 1q21 region. The most-associated genotyped SNP is shown in blue, and the color of the remaining markers reflects the linkage disequilibrium (r²) with the top SNP in each panel (increasing red hue associated with increasing r²). The recombination rate (right-hand y axis) is plotted in light blue and is based on the CEU HapMap population. Exons for each gene are represented by vertical bars, based on all isoforms available from the March 2006 UCSC Genome Browser assembly. (D) Minor allele frequency for the TCHH SNP rs11803731, based on the Human Genome Diversity Project. (E) Frequency of straight (orange bars), wavy (green bars), and curly (blue bars) hair as a function of the rs11803731 genotype in a sample of unrelated individuals (n[AA] = 43; n[AT] = 493; n[TT] = 1132). With more T alleles, the proportion of straight hair increases. Vertical bars correspond to the 95% confidence intervals on the prevalence.