Researchers obtained quantitative skin pigmentation measures (M-index) in the inner upper arm of the participants, using a portable reflectometer (N = 305). Quantitative measures of iris color (expressed as L*, a* and b* CIELab coordinates) were extracted from high-resolution iris pictures (N = 342). The study also measured the color differences between the pupillary and ciliary regions of the iris (e.g., iris heterochromia). DNA samples were genotyped with Illuminas Infinium Multi-Ethnic Global Array (MEGA) and imputed using the 1000 Genomes Phase 3 samples as reference haplotypes. For skin pigmentation, we did not observe any genome-wide significant signal. Researchers followed-up in three independent Chinese samples the lead SNPs of five regions showing multiple common markers (minor allele frequency 5 percent) with good imputation scores and suggestive evidence of association (p-values < 10 5). One of these markers, rs2373391, which is in an intron of the ZNF804B gene on chromosome 7, was replicated in one of the Chinese samples (p = 0.003). For iris color, researchers observed genome-wide signals in the OCA2 region on chromosome 15. This signal is driven by the non-synonymous rs1800414 variant, which explains 11.9 percent, 10.4 percent, and 6 percent of the variation observed in the b*, a* and L* coordinates in the sample, respectively; however, the OCA2 region was not associated with iris heterochromia. The researchers advise that additional genome-wide association studies in East Asian samples will be necessary to further disentangle the genetic architecture of pigmentary traits in East Asian populations. (publisher abstract modified)
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