February 08, 2017 –
Genetic predisposition may go in both ways, the positive and the negative. Usually, when we talk about genetic predisposition, there is an immediate association with some unwanted reactions of individuals towards drugs (e.g., abacavir-induced hypersensitivity reaction in carriers of the HLA-B*5701
allele) or some inheritable diseases (e.g., cystic fibrosis caused by mutations in the CFTR gene
) which may make the life of the affected individual very difficult.
Here, we have a very enjoyable positive example of genetic predisposition to the contrary. The rare human individuals who are carriers of a particular allelic variant of the ABCC11 gene do not emit smelly body odor from sweaty armpits. As an add on, individuals with this rare allelic variant are also more likely to produce dry earwax rather than wet or sticky wax.
Actually, the ABCC11
gene is present in the human genome as two alleles
, differing in one nucleotide
also known as a single nucleotide polymorphism (SNP
). A SNP in the ABCC11
gene on chromosome 16 at base position 538 of either a guanine
(G) or adenine
(A) gives rise to two allelic variants of the ABC11 gene (G- or A-allele) and as a result, humans can be of three possible genotypes
(GG, GA, or AA), and these alleles are responsible for the occurrence of multiple distinct human phenotypes
. The phenotypes expressed by the genotypes include cerumen
type (wet or dry ear wax), osmidrosis
(odor associated with sweat
caused by excessive apocrine
secretion), and possibly breast cancer risk. The GG or GA genotype produces the wet ear wax phenotype (sticky and brown colored) and acrid sweat odor and is the dominant allele. The AA genotype produces the dry ear wax phenotype (dry and flaky) and mildly odored sweat.
As it turns out, most human individuals in East Asia and 30% to 50% of those in Southern Asia, the Pacific Islands, Central Asia, Asia Minor and indigenous Americans do not have smelly armpits, because they are of the AA genotype. And most astonishingly, almost all Korean individuals (about 95%) are of the AA genotype, which in turn saves their armpits from smelling awful.
Overall, while the AA genotype is frequent in Asian populations, it is rare in Caucasians and in ethnicities from Africa ( from 0% to 3% only). Actually, a study, published in the Journal of Investigative Dermatology
in 2013, surveyed 6,495 British mothers and found that 2% of them were of the AA genotype at the ABCC11 gene locus. In that particular study, blood samples were taken from the women in the study, their genotypes determine, and their responses to a questionnaire regarding hygienic rituals and use of products were recorded. The researchers discovered that the women who did not produce body odor (the AA genotypes) were probably unaware to that fact and still used deodorant on a daily basis. In a concept of personalized genetics in personalized hygiene, these genetically privileged persons would spend their money to no avail and even expose their skin to what may in many instances not be good for their skin. While the abundance of the AA genotype in Caucasians and people of African descent pales in comparison to the abundance in East Asian populations, it does nevertheless mean that these persons could do perfectly well without ever using a deodorant as could, for example, the vast majority of Korean people.