January 30, 2006

Earwax type determined by single letter of DNA

From the paper:
Earwax (cerumen) is a secretory product of ceruminous apocrine glands. Human earwax is a mendelian trait consisting of wet and dry types1. The wet earwax is brownish and sticky, whereas the dry type lacks cerumen. The wet cerumen phenotype is completely dominant to the dry type. The dry type is seen frequently (80–95%) among East Asians2, 3, 4, but uncommon (0–3%) in populations of European and African origins. Intermediate frequencies (30–50%) of the dry type are seen in populations of Southern Asia, the Pacific Islands, Central Asia and Asia Minor, as well as among the Native North American and Inuit of Asian ancestry2, 5. These figures show geographical gradient distributions. Earwax type may play a role in the axillary odor and possibly in breast cancer susceptibility6, although the association with breast cancer remains controversial7. Using a linkage analysis, we have previously assigned the earwax gene locus to the pericentromeric region of chromosome 16 (ref. 8).
Distribution of allele A:

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See also Gene for ear wax (BBC).

Nature Genetics (published online)

A SNP in the ABCC11 gene is the determinant of human earwax type

Koh-ichiro Yoshiura et al.

Human earwax consists of wet and dry types. Dry earwax is frequent in East Asians, whereas wet earwax is common in other populations. Here we show that a SNP, 538G right arrow A (rs17822931), in the ABCC11 gene is responsible for determination of earwax type. The AA genotype corresponds to dry earwax, and GA and GG to wet type. A 27-bp deletion in ABCC11 exon 29 was also found in a few individuals of Asian ancestry. A functional assay demonstrated that cells with allele A show a lower excretory activity for cGMP than those with allele G. The allele A frequency shows a north-south and east-west downward geographical gradient; worldwide, it is highest in Chinese and Koreans, and a common dry-type haplotype is retained among various ethnic populations. These suggest that the allele A arose in northeast Asia and thereafter spread through the world. The 538G right arrow A SNP is the first example of DNA polymorphism determining a visible genetic trait.


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