TCHH rs11803731: What Your Genotype Means for Hair Texture
The rs11803731 variant is a single-nucleotide polymorphism located within the TCHH gene. It is statistically associated with variations in hair morphology, specifically influencing the likelihood of having straight versus curly hair in populations of European ancestry.
What each genotype means
Associated with curlier hair
This genotype is statistically associated with a higher likelihood of having curly hair compared to those with the T allele. Research indicates this variant in the TCHH gene influences hair morphology, though it is only one of many genetic and environmental factors that determine hair texture.
This genotype is less common in European populations compared to the TT genotype.
Intermediate hair texture
Individuals with this heterozygous genotype often exhibit hair texture characteristics that fall between those associated with the AA and TT genotypes. As hair morphology is a complex trait influenced by multiple genes, this result should be viewed as a minor contributor to your overall hair appearance.
This is a common genotype found in many individuals of European ancestry.
Associated with straighter hair
This genotype is statistically associated with a higher likelihood of having straighter hair. While this variant in the TCHH gene is a known marker for hair morphology, it does not solely determine hair texture, as many other genetic factors are involved.
This is the most common genotype in European populations, where the T allele is more prevalent.
Understanding the rs11803731 Variant
The rs11803731 variant is a specific genetic change, or single-nucleotide polymorphism (SNP), located on chromosome 1 within the TCHH gene region. In genetics, a SNP represents a variation at a single position in the DNA sequence. This particular variant is notable because it is a nonsynonymous change, meaning it alters the protein sequence by replacing the amino acid lysine with methionine at position 790 (p.L790M). Because of its location and potential impact on protein structure, researchers have long investigated whether this specific change is the functional driver behind observed differences in hair texture. While it is a well-studied marker in European populations, it is important to note that it exists within a region of high linkage disequilibrium, meaning it is often inherited alongside other nearby genetic variations that may also contribute to the observed physical traits.
The Role of the TCHH Gene
The TCHH gene provides the instructions for producing a protein called trichohyalin. This protein is primarily expressed in the inner root sheath of hair follicles, which are the specialized structures in the skin responsible for hair growth. Trichohyalin plays a critical role in the structural integrity of the hair shaft. It functions by forming cross-linked complexes with itself and with keratin intermediate filaments, effectively acting as a structural scaffold that provides mechanical strength to the developing hair. By reinforcing the cornified envelope of the inner root sheath cells, trichohyalin helps shape the hair as it emerges from the follicle. Variations in the TCHH gene, such as rs11803731, are thought to influence this process, potentially altering the mechanical properties of the hair follicle and, consequently, the final shape and texture of the hair strand.
Research and Evidence Strength
The association between rs11803731 and hair curliness is supported by multiple genome-wide association studies (GWAS). Research has consistently identified this locus as a significant signal for hair morphology in individuals of European descent. However, the evidence strength is considered limited in terms of predictive power. While the variant is statistically significant, it explains only a small proportion of the total heritability of hair curliness. Furthermore, the effect is highly ancestry-specific; the associations found in European populations are not necessarily replicated in other continental groups, where different genes, such as EDAR, play more prominent roles in hair texture. Because hair shape is a complex, polygenic trait influenced by many genes and environmental factors, this single SNP should be viewed as one small piece of a much larger, incomplete genetic puzzle rather than a definitive determinant of hair texture.
Population Frequency and Distribution
The frequency of the rs11803731 variant varies significantly across different global populations. In European populations, the minor allele frequency is approximately 0.37. This relatively high frequency allows researchers to study its effects effectively within these groups. In contrast, the variant is much less common or absent in other ancestral groups, which underscores the importance of considering population background when interpreting genetic data. Because the variant is largely specific to European ancestry, its utility as a predictor for hair texture is restricted to those populations. Geneticists use these frequency differences to understand the independent evolutionary histories of hair shape variation across different continents, noting that different genetic pathways have evolved to influence hair structure in diverse human populations.
Interpreting Your Genetic Information
If you have received information about your rs11803731 genotype, it is important to understand that this data is for educational purposes only. While the variant is associated with hair texture, it is not a diagnostic tool, and it cannot predict your hair type with absolute certainty. Hair morphology is influenced by a complex interplay of multiple genes, as well as environmental and developmental factors. You cannot use this information to make medical decisions or health assessments. If you have concerns about your hair or skin health, or if you are interested in how genetics might influence other aspects of your biology, it is best to consult with a qualified healthcare professional or a genetic counselor. They can provide context and help you understand the limitations of genetic testing in the context of your overall health and personal history.
How common is this variant?
The minor allele frequency for rs11803731 is approximately 0.37 in European populations, with significant variation observed across different global ancestral groups.
Frequently asked questions
Does the rs11803731 variant determine if I have curly hair?
No, this variant does not determine your hair texture on its own. It is one of many genetic factors that contribute to hair shape, and it only explains a small portion of the trait's variation.
Can I use this SNP to predict my children's hair type?
No, you cannot use this SNP to accurately predict the hair texture of your children. Hair shape is a complex, polygenic trait influenced by many genes and environmental factors that are not fully captured by this single variant.
Is the rs11803731 variant associated with any health conditions?
The rs11803731 variant is primarily studied for its association with hair morphology. There is no evidence suggesting it is a diagnostic marker for any medical condition.
Why is this variant only relevant to European populations?
Genetic variants often show different frequencies and associations across populations due to independent evolutionary histories. The TCHH variant is a known example of an association that is specific to European ancestry.
Sources & further reading
Educational information only, last refreshed 10/13/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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Common polymorphism in the trichohyalin locus strongly predictive of straight versus curly hair texture morphology in Europeans.
Key genetic variant within trichohyalin that shapes hair curliness, wave pattern, and texture in individuals of European ancestry.
Missense coding variant in trichohyalin that plays a major determinant role in human straight versus curly hair morphology.
This variant in the trichohyalin gene influences hair texture, specifically associated with straight, wavy, or curly hair phenotypes.
Variant in the TCHH gene associated with variation in hair curl structure.
Trichohyalin gene variant associated with straight versus curly hair morphology and texture differences in populations of European descent.