Abstract
BackgroundEye and hair colour is highly variable in the European population, and is largely genetically determined. Both linkage and association studies have previously been used to identify candidate genes underlying this variation. Many of the genes found were previously known as underlying mutant mouse phenotypes or human genetic disease, but others, previously unsuspected as pigmentation genes, have also been discovered.ResultsWe assayed the hair of a population of individuals of Scottish origin using tristimulus colorimetry, in order to produce a quantitative measure of hair colour. Cluster analysis of this data defined two groups, with overlapping borders, which corresponded to visually assessed dark versus red/light hair colour. The Danish population was assigned into categorical hair colour groups. Both cohorts were also assessed for eye colour. DNA from the Scottish group was genotyped at SNPs in 33 candidate genes, using 384 SNPs identified by HapMap as representatives of each gene. Associations found between SNPs and colorimetric hair data and eye colour categories were replicated in a cohort of the Danish population. The Danish population was also genotyped with SNPs in 4 previously described pigmentation genes. We found replicable associations of hair colour with the KITLG and OCA2 genes. MC1R variation correlated, as expected, with the red dimension of colorimetric hair colour in Scots. The Danish analysis excluded those with red hair, and no associations were found with MC1R in this group, emphasising that MC1R regulates the colour rather than the intensity of pigmentation. A previously unreported association with the HPS3 gene was seen in the Scottish population. However, although this replicated in the smaller cohort of the Danish population, no association was seen when the whole study population was analysed.ConclusionsWe have found novel associations with SNPs in known pigmentation genes and colorimetrically assessed hair colour in a Scottish and a Danish population.
Highlights
Eye and hair colour is highly variable in the European population, and is largely genetically determined
Whilst variation in skin pigmentation is notable between populations, hair colour variation is most notable within populations of European origin [1,2]
Association analyses between hair colour and SNPs in Europeans have been more informative than linkage analyses and have revealed associations with several genes, most already known from mouse or human pigmentary mutations; SLC45A2, TYR, OCA2, KITLG, ASIP, and TYRP1 but others not previously implicated in pigmentation; SLC24A4, IRF4 and TPCN2 [4,5,15,16][17]
Summary
Eye and hair colour is highly variable in the European population, and is largely genetically determined. Both linkage and association studies have previously been used to identify candidate genes underlying this variation. Blond and red hair colours are commonly seen variations in Europeans, but are rare in other populations. Both linkage studies in families and genome-wide association studies in populations have identified genetic factors that determine hair and eye colour. These SNPs have a weak association with hair colour, but there are notably stronger associations with hair colour and haplotypes across the OCA2 gene itself [4]
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