Human genetics offers a remarkable glimpse into how our bodies differ. Even minor alterations in our genetic code can lead to noticeable physical traits. This variation highlights the relationship between our genes and the outward characteristics we exhibit.
The ABCC11 Gene: A Genetic Blueprint
The ABCC11 gene, located on chromosome 16 at band 16q12.1, codes for an ATP-binding cassette (ABC) transporter protein. ABC transporters are a family of proteins that move molecules across cell membranes. These proteins use energy from ATP (adenosine triphosphate) to pump substances in and out of cells.
The ABCC11 protein is a member of the MRP (Multidrug Resistance-Related Protein) subfamily of ABC transporters. This subfamily transports molecules like bile acids, conjugated steroids, and cyclic nucleotides. The ABCC11 gene provides instructions for a cellular “pump” that influences various physiological processes.
ABCC11 and Its Influence on Body Traits
The ABCC11 gene directly influences two human traits: earwax type and underarm odor. The protein transports specific molecules within apocrine sweat glands, found in areas like the armpits, which also produce earwax.
For earwax, the ABCC11 protein’s function determines whether earwax is wet and sticky or dry and flaky. Wet earwax, typically yellow or brown, results from a functional ABCC11 protein transporting lipids and proteins into the ear canal. Dry earwax, often grayish or white, occurs when the ABCC11 protein is non-functional, secreting fewer components.
For underarm odor, the ABCC11 protein transports odorless precursor compounds into apocrine sweat. Skin bacteria then break these precursors down into volatile, odor-causing compounds. A functional ABCC11 protein facilitates this transport, contributing to more noticeable body odor. Conversely, a non-functional protein reduces the availability of these precursors, leading to significantly less odor.
The Unique Variant in Asian Populations
A specific genetic variant of the ABCC11 gene is highly prevalent in East Asian populations. This variation stems from a single nucleotide polymorphism (SNP) at position 538, where guanine (G) is replaced by adenine (A). This change, 538G>A (rs17822931), alters the protein, making it non-functional or less functional.
Individuals with the AA genotype for this SNP typically have dry earwax and significantly reduced underarm odor. The non-functional ABCC11 protein cannot efficiently transport the odor-causing precursors, leading to a different metabolic environment for skin bacteria. This variant is found in 80% to 95% of East Asian populations, including Chinese, Japanese, and Korean individuals.
In contrast, this specific variant is rare in people of European and African descent, where the G allele, associated with wet earwax and more pronounced body odor, is more common. The prevalence of the dry earwax allele shows a geographical gradient, being highest in East Asia and decreasing towards the west and south. This suggests that the “A” allele likely originated in Northeast Asia and subsequently spread.
Beyond Earwax and Odor: Broader Significance
The ABCC11 gene exemplifies how a single genetic change can lead to clear differences in human traits. Its variant distribution across populations provides insights into human migration and evolutionary adaptations. For instance, its high frequency in East Asian populations and indigenous peoples of the Americas, along with its presence in ancient DNA from Northern China, suggests a long history of this trait in these regions.
The ABCC11 A allele has been linked to adaptation to colder climates, as diminished sweat gland activity could aid in body heat preservation. This gene also holds potential in forensic science, acting as a distinct marker for ancestry, particularly East Asian heritage. Understanding these genetic variations offers valuable data for genetic anthropology and illuminates human biological diversity.