Genetic traits refer to the higher frequency of specific gene variants within a defined population compared to others. These population-level genetic patterns arise from a shared history of relative geographic isolation, historical migrations, and environmental pressures that favor certain traits. The genetic profile of the Korean population is largely the result of ancient admixture between northern East Asian lineages, tracing back to hunter-gatherers of the Siberian region, and southern lineages, linked to Neolithic farmers from the Yellow and Yangtze River basins. This history contributed to a distinct and comparatively homogeneous genetic makeup with specific allele frequencies that influence both physical appearance and internal biological function.
Observable Physical Characteristics
The most noticeable genetic traits manifest in physical appearance, resulting from specific gene variants becoming highly prevalent. The characteristic straight and thick hair common in the population is primarily influenced by variations in genes such as EDAR and FGFR2. The EDAR370A variant is specifically associated with hair that has a circular cross-sectional shape and a larger diameter, contributing to its straightness and strength.
Another prominent feature is the epicanthic fold, a skin fold of the upper eyelid that covers the inner corner of the eye, often resulting in the appearance of a “monolid.” While multiple genes contribute to this trait, the EDAR gene’s 370A variant is a major factor linked to this specific eye morphology across East Asian populations.
Other common traits include specific variations in earwax and body odor. Many Koreans possess a gene variant in ABCC11 that results in dry earwax and a reduced production of body odor, a trait highly prevalent across East Asia. This variation is also linked to a lower incidence of breast cancer in certain populations, suggesting a complex interplay between seemingly unrelated genetic effects.
Distinct Metabolic and Enzyme Traits
Genetic variations frequently affect the body’s ability to process common substances, particularly alcohol and dairy consumption. One prevalent trait is the reduced ability to properly metabolize alcohol, known as the “alcohol flush” reaction. This reaction is caused by a non-functional variant of the ALDH2 gene (Aldehyde Dehydrogenase 2).
The inactive enzyme cannot efficiently break down acetaldehyde, the toxic byproduct of alcohol metabolism, causing it to accumulate rapidly. This buildup triggers physical symptoms like facial flushing, nausea, and rapid heartbeat, acting as a strong deterrent to heavy drinking. Approximately 30% of the Korean population carries this specific genetic deficiency, which influences drinking behavior and carries implications for health risks related to alcohol exposure.
Another common metabolic variation is lactase non-persistence (LNP), the genetic condition underlying lactose intolerance. The ability to digest lactose into adulthood, known as lactase persistence, is the result of a genetic mutation that arose in populations with a long history of dairy farming. However, the prevalence of the LNP genotype in the Korean population is near 100%, reflecting a historical lack of reliance on dairy products after infancy.
LNP is caused by a reduction in the production of the lactase enzyme after childhood, which is regulated near the LCT gene. The resulting lack of the lactase-persistence genotype means undigested lactose travels to the large intestine where it causes common gastrointestinal symptoms.
Genetic Health Predispositions
The Korean population exhibits distinct patterns of disease risk, notably a globally high incidence of stomach cancer. This elevated risk results from a complex interaction between environmental factors, such as high rates of Helicobacter pylori infection, and specific genetic susceptibilities. Genetic studies have identified the PSCA gene (Prostate Stem Cell Antigen) as a significant susceptibility factor.
A genetic predisposition to cancer is also seen in families with Hereditary Nonpolyposis Colorectal Cancer (HNPCC), where the overall risk of gastric cancer is estimated to be 2.1-fold greater than in the general population. Specific variants of the p53 tumor suppressor gene also correlate with the location and aggressiveness of tumors.
While the incidence of thyroid cancer is historically high, studies suggest this is largely due to increased screening and environmental factors, though family history indicates inherited susceptibilities remain a risk factor.
In contrast to many Southeast Asian groups, the prevalence of the inherited blood disorder Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency is low, estimated between 0.4% and 0.9%. G6PD deficiency is an X-linked recessive disorder that causes red blood cell breakdown when exposed to certain oxidative stressors, such as specific medications or foods. The low frequency of this gene variant is a notable distinction.
Pharmacogenetic Considerations
Genetic differences influence how individuals respond to medications, a field known as pharmacogenetics. Variations in Cytochrome P450 (CYP) enzymes, a superfamily of enzymes in the liver that metabolize most drugs, are frequently observed in the Korean population. These variations can result in an individual being a “poor metabolizer” or an “intermediate metabolizer,” which directly affects drug efficacy and dosing, potentially leading to toxicity or lack of effectiveness.
For example, the CYP2C19 enzyme metabolizes several common medications, including anti-depressants and blood thinners. Nearly half, or 48.74%, of the Korean population is classified as an intermediate metabolizer for this enzyme due to gene variants. This suggests that standard drug doses may be metabolized more slowly or quickly, potentially requiring dosage adjustments.
Specific variants of the CYP2C9 enzyme also show decreased catalytic efficiency, impacting the metabolism of drugs like nonsteroidal anti-inflammatory drugs. Another notable finding is the high frequency of the high-risk 3 allele in the CYP4F2 gene, which is involved in Vitamin K metabolism, occurring in 34.72% of the population. Understanding these precise genetic variations is important for personalized medicine and safe drug prescription.