When I was in college a Korean American friend confided to me that his roommate had an issue. He had seen a q-tip in the waste-bin, and what was at the end of it was shocking to him. What my friend was describing was wet earwax (Google it yourself if you want to see it). As this was the first time he was living with a non-Korean he had assumed that everyone’s earwax was dry, like his own. The maps above and to the left show you the frequencies of the allele which has an extremely strong correlation with this trait. In Korea the frequency of dry earwax is close to 100%. Since the expression pattern for dry earwax is recessive, you need two copies of the derived allele, so in any population where the ancestral variant exists in appreciate frequencies you’ll have the wet variant of the trait.
This is why in 2006 a Japanese group published research in this area, A SNP in the ABCC11 gene is the determinant of human earwax type. A substantial minority of Japanese happen to have wet earwax. And it turns out that wet earwax has some other associations of interest.
Axillary osmidrosis is scientific for body odor. These results show a very strong association between someone with the ancestral allele which results in wet earwax, and strong body odor. Obviously this is a “news you can use” sort of result, so no surprise at seeing this paper: Dependence of Deodorant Usage on ABCC11 Genotype: Scope for Personalized Genetics in Personal Hygiene:
Earwax type and axillary odor are genetically determined by rs17822931, a single-nucleotide polymorphism (SNP) located in the ABCC11 gene. The literature has been concerned with the Mendelian trait of earwax, although axillary odor is also Mendelian. Ethnic diversity in rs17822931 exists, with higher frequency of allele A in east Asians. Influence on deodorant usage has not been investigated. In this work, we present a detailed analysis of the rs17822931 effect on deodorant usage in a large (N~17,000 individuals) population cohort (the Avon Longitudinal Study of Parents and Children (ALSPAC)). We found strong evidence (P=3.7 × 10−20) indicating differential deodorant usage according to the rs17822931 genotype. AA homozygotes were almost 5-fold overrepresented in categories of never using deodorant or using it infrequently. However, 77.8% of white European genotypically nonodorous individuals still used deodorant, and 4.7% genotypically odorous individuals did not. We provide evidence of a behavioral effect associated with rs17822931. This effect has a biological basis that can result in a change in the family’s environment if an aerosol deodorant is used. It also indicates potential cost saving to the nonodorous and scope for personalized genetics usage in personal hygiene choices, with consequent reduction of inappropriate chemical exposures for some.
I don’t want to get into the biology of this is too much detail. Suffice it to say that the SNP in ABCC11 has a lot of effects. It looks like there might have been a selection event to drive up its frequency at some point. I’m intrigued at the fact that among European populations it is among Sardinians that the derive allele is least common. If it was selection I’m pretty sure don’t know the target phenotype. Less body odor is probably simply a nice side effect. Ultimately though this is personal. If you read NPR’s stupid Code Switch blog you will have seen that Study Says Your Race Determines Your Earwax Scent. Actually, obviously no. This gene has a high between population difference as far as genes go, but the wet and dry phenotypes segregate in many families, and are found in appreciable frequencies in many populations. Both alleles are found in my own immediate family. My wife and myself carry both alleles. We’re heterozygotes. My daughter is a homozygote for the ancestral variant. My soon-to-be-born son is homozygote for the derived variant. Perhaps we’ll be saving on deodorant purchases?