TCHH rs17646946: What Your Genotype Means for Hair Morphology
The rs17646946 variant is a genetic marker located near the TCHH gene, which provides instructions for making the protein trichohyalin. Research suggests this variant is associated with variations in human hair morphology, specifically influencing the tendency toward straight or curly hair.
What each genotype means
Associated with straighter hair
Research indicates that this genotype is associated with a tendency toward straighter hair morphology in individuals of European descent. This variant in the TCHH gene influences the structure of the hair follicle, though hair texture is a complex trait influenced by multiple genetic and environmental factors.
This genotype is common in European populations, where the minor allele frequency for this variant is approximately 0.40 to 0.50.
Intermediate hair texture
Individuals with this heterozygous genotype may exhibit hair texture that falls between the extremes of straight and curly. Because hair morphology is a polygenic trait, this specific genotype contributes to the overall variation in hair shape observed in the population.
This genotype is frequently observed in European cohorts, reflecting the high prevalence of both alleles in these populations.
Associated with curlier hair
This genotype is statistically associated with a higher likelihood of having curlier or wavier hair in European populations. While the TCHH gene plays a role in determining hair morphology, it is one of several genetic factors that define the final appearance of your hair.
This genotype is common among individuals of European ancestry, occurring at frequencies consistent with the observed population distribution of the variant.
Understanding the rs17646946 Variant
The rs17646946 variant is a single nucleotide polymorphism (SNP) located on chromosome 1 in the q21.3 region. This region is known for housing several genes involved in the development of the hair follicle and the structure of the hair shaft. While rs17646946 is often cited in studies regarding hair shape, it is important to note that it is located upstream of the TCHH gene rather than within its coding sequence. Because of its proximity, it is frequently studied alongside other variants in the same genomic neighborhood that may directly alter the function of the trichohyalin protein. Geneticists use such markers to track how specific segments of DNA are inherited and how they correlate with physical traits across different populations.
The Role of the TCHH Gene
The TCHH gene encodes a protein called trichohyalin, which is essential for the structural integrity of hair. Trichohyalin acts as a cross-linking protein that binds to keratin filaments, helping to organize them into the rigid, organized structures that form the hair shaft. By creating these linkages, the protein contributes to the mechanical strength and shape of the hair. When the TCHH gene functions normally, it supports the development of hair with standard texture and shape. Rare, severe mutations in this gene have been linked to conditions like uncombable hair syndrome, where the hair structure is significantly altered. In the context of common variation, however, the gene is thought to contribute to the subtle, natural differences in hair curliness observed across the human population.
Research and Evidence Strength
The association between the TCHH region and hair morphology is supported by genome-wide association studies (GWAS). Researchers have identified that variants in this region contribute to the variance in hair shape, with some alleles showing a statistical correlation with straighter hair. However, the evidence for rs17646946 specifically is considered limited. While it serves as a useful marker in genetic studies, it is often part of a larger complex of variants that collectively influence hair texture. It is crucial to understand that hair shape is a polygenic trait, meaning it is influenced by many different genes and environmental factors working in concert. No single SNP, including rs17646946, can definitively predict an individual's hair type, and the statistical associations observed in large cohorts do not guarantee a specific physical outcome for any one person.
Population Frequency
The frequency of the alleles associated with rs17646946 varies significantly across different ancestral groups. In European populations, the minor allele frequency (MAF) is typically observed in the range of 0.40 to 0.50. This indicates that the variant is quite common in these groups. Conversely, the frequency of this variant is notably lower in many African and East Asian cohorts. These differences in allele frequency reflect the complex history of human migration and the selective pressures that have shaped physical traits like hair texture over thousands of years. Because the variant is more prevalent in certain populations, its association with hair morphology is most robustly documented in those specific groups, highlighting the importance of considering ancestry when interpreting genetic data.
Interpreting Your Genetic Information
If you have received information about your rs17646946 genotype, it is helpful to view it as a small piece of a much larger biological puzzle. This variant is a tool for scientific research into human diversity and the genetic basis of physical traits, but it is not a diagnostic marker for any health condition. You cannot use this information to predict your hair type with certainty, nor does it provide information about your overall health or medical risk. Because hair morphology is influenced by a wide array of genetic and environmental factors, this SNP should be viewed as a point of interest rather than a definitive instruction. If you have concerns about hair health or changes in hair texture, it is always best to consult with a dermatologist or a qualified healthcare professional who can provide personalized guidance based on your physical presentation.
How common is this variant?
The rs17646946 variant has a minor allele frequency of approximately 0.40-0.50 in European populations, while it is found at lower frequencies in African and East Asian cohorts.
Frequently asked questions
Can this SNP predict if my hair will be curly or straight?
No, this SNP cannot definitively predict your hair type. Hair morphology is a complex trait influenced by many different genes and environmental factors, and this variant only accounts for a small portion of that variation.
Is rs17646946 associated with any medical conditions?
There is no evidence that this specific variant is associated with medical conditions. While the TCHH gene is involved in hair structure, this SNP is a common marker used in studies of normal physical variation.
Why is the evidence for this variant considered limited?
The evidence is considered limited because the variant is often a marker for a broader region of DNA rather than a direct cause of a physical change. Additionally, the effect size of any single SNP on a complex trait like hair shape is typically very small.
Does my genotype change over time?
No, your genotype is determined at conception and remains the same throughout your life. While your hair texture may change due to age, hormones, or environmental factors, your underlying DNA sequence does not change.
Sources & further reading
Educational information only, last refreshed 9/20/2026. 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.
Trichohyalin variant associated with hair curliness in individuals of European descent.
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.