Sunday, October 05, 2008

Predicting hair color from genes

It seems like we're getting closer to understanding the genetic basis of traits like skin, hair and eye pigmentation. Although it is generally assumed that it will be difficult to fully grasp the genetics of complex traits, it could be within reach in the near-term for these types of traits. Understanding the genetic basis of these traits will provide some guiding principles for uncovering the genetic basis of more 'complex' complex traits, as well as about the evolutionary genetic process, population histories, and interactions with environmental factors.
So what do we learn from this paper (see abstract below) on the association between SLC45A2 variants and hair color among Polish subjects?
First, from the intro, with respect to predicting red hair color:
"Nowadays, red hair phenotype is being predicted using
assays that rely on examination of the single MC1R gene, and this allows correct inference in more than 90% of cases (Grimes et al. 2001; Branicki et al. 2007)."
Back to this study, they basically find a rare variant in SLC45A2 that increases a person's odds of having black hair by about seven.

"However, in the present study, 3.6% of red-haired individuals were found to have the L374 allele associated with darker pigmentation. All of them had two MC1R alterations, which are considered as major function mutations strongly affecting receptor performance (data not present). All these individuals had fair skin and blue eyes. This indicates a predominant role of the MC1R gene."
Association of the SLC45A2 gene with physiological human hair colour variation
Wojciech Branicki, Urszula Brudnik, Jolanta Draus-Barini, Tomasz Kupiec and Anna Wojas-Pelc
Journal of Human Genetics Early online
Abstract: Pigmentation is a complex physical trait with multiple genes involved. Several genes have already been associated with natural differences in human pigmentation. The SLC45A2 gene encoding a transporter protein involved in melanin synthesis is considered to be one of the most important genes affecting human pigmentation. Here we present results of an association study conducted on a population of European origin, where the relationship between two non-synonymous polymorphisms in the SLC45A2 gene — rs26722 (E272K) and rs16891982 (L374F) — and different pigmentation traits was examined. The study revealed a significant association between both variable sites and normal variation in hair colour. Only L374F remained significantly associated with hair colour when both SNPs were included in a logistic regression model. No association with other pigmentation traits was detected in this population sample. Our results indicate that the rare allele L374 significantly increases the possibility of having black hair colour (OR = 7.05) and thus may be considered as a future marker for black hair colour prediction.

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