CYP1B1 rs1800440: What Your Genotype Means
The rs1800440 polymorphism is a well-studied single nucleotide change in the CYP1B1 gene, causing an amino acid substitution from asparagine to serine (Asn453Ser). This variant alters the metabolic activity of the cytochrome P450 1B1 enzyme, which is involved in processing endogenous hormones such as estrogens as well as exogenous environmental compounds. Research has examined rs1800440 for subtle influences on hormone-related traits, physical pigmentation patterns, and complex inflammatory hair conditions, although its overall clinical impact remains classified as benign or limited in effect.
What each genotype means
Common ancestral genotype
This is the most common genotype for this variant in many populations. Research into this variant, also known as Asn453Ser, has explored its potential role in hormone metabolism and various health conditions, but findings remain inconsistent and limited. There is no consensus on a specific clinical impact for this genotype.
This is the major allele genotype, found in the majority of individuals across most global populations.
Heterozygous variant profile
You carry one copy of the variant allele, which results in a change from asparagine to serine at position 453 of the CYP1B1 protein. While some studies have investigated whether this change alters enzyme activity or influences susceptibility to certain conditions, the evidence is currently mixed and inconclusive. You should not interpret this as a diagnostic finding.
Carried by a significant portion of the population, with a minor allele frequency typically ranging between 0.15 and 0.20 in European ancestries.
Homozygous variant profile
You carry two copies of the variant allele, which leads to the Asn453Ser amino acid substitution in the CYP1B1 enzyme. Scientific literature has examined this genotype in the context of estrogen metabolism and various disease risks, but results have been inconsistent and often show no significant association. This finding is generally considered to have limited clinical significance.
This genotype is less common than the others, occurring in a smaller percentage of individuals, particularly in European populations, and is rare in East Asian populations.
Genetic Architecture of rs1800440
The single nucleotide polymorphism (SNP) rs1800440 is located on chromosome 2 within the coding region of the CYP1B1 gene. At the nucleotide level, it represents an adenine (A) to guanine (G) transition (c.1358A>G), which changes the 453rd amino acid of the encoded protein from asparagine to serine (p.Asn453Ser). Because it directly alters the amino acid sequence, it is considered a missense variant. In genetic testing and research, it is frequently evaluated alongside other common missense variants in the same gene, such as Arg48Gly (rs10012) and Leu432Val (rs1056836). Clinical databases such as ClinVar classify rs1800440 primarily as benign or likely benign regarding classical Mendelian disorders. Rather than acting as a disease-causing disruption, this variant serves as a common functional modifier within human populations, gently modulating baseline biochemical efficiency without breaking the overall reading frame of the protein.
Biological Function of the CYP1B1 Enzyme
The CYP1B1 gene provides instructions for producing cytochrome P450 1B1, a specialized phase I xenobiotic-metabolizing enzyme. Embedded largely in the endoplasmic reticulum of extrahepatic tissues, CYP1B1 plays an essential role in catalyzing the oxidative metabolism of diverse substrates. These substrates include polycyclic aromatic hydrocarbons, dietary pro-carcinogens, and endogenous signaling molecules such as 17beta-estradiol. Specifically, CYP1B1 preferentially hydroxylates estradiol at the C-4 position to produce 4-hydroxyestradiol, a reactive catechol estrogen metabolite that participates in tissue remodeling and hormonal signaling pathways. Biochemical investigations show that the Asn453Ser substitution caused by rs1800440 can decrease the functional stability or catalytic velocity of the enzyme toward certain substrates. Consequently, individuals carrying the G allele may exhibit subtle shifts in their ratio of estrogen metabolites and foreign compound breakdown rates compared to those carrying the ancestral A allele.
Research Associations and Evidence Strength
Over the past two decades, rs1800440 has been investigated across a broad range of complex traits and conditions, though findings are nuanced. Genome-wide and candidate gene association studies have linked CYP1B1 variants to differences in physical pigmentation and hair follicle biology. Notably, recent studies in dermatological genetics have identified rs1800440 in cohorts evaluating frontal fibrosing alopecia, where the minor G allele has been investigated for potential protective or modulatory associations in concert with immune loci such as HLA-B*07:02. In oncological epidemiology, multiple meta-analyses evaluating colorectal cancer and hormone-sensitive tissues have found that rs1800440 alone does not significantly increase disease risk, showing conflicting or null results across large patient groups. Thus, current scientific consensus views the evidence connecting rs1800440 to definitive disease outcomes as limited, reflecting weak statistical modifiers rather than high-penetrance risk factors.
Population Frequency and Diversity
The distribution of rs1800440 varies substantially across global ancestral populations, illustrating evolutionary divergence in metabolic genes. In European populations, the minor G (Ser) allele is relatively common, with an observed minor allele frequency typically hovering between 14% and 20%. Population data compiled in repositories such as gnomAD reflect an allele frequency of roughly 18% in non-Finnish Europeans. By contrast, the G allele is far less common in East Asian populations, often registering at frequencies around 1% or less. This geographic variability means that the homozygous GG genotype is observed in approximately 2% to 4% of European cohorts but is exceptionally rare in East Asian lineages. Understanding these ancestral disparities is essential for genetic epidemiologists, as association signals detected in one ancestral group cannot be assumed to replicate identically in another without localized confirmation.
Practical Implications and Clinical Guidance
Discovering your rs1800440 genotype through direct-to-consumer genetic testing provides intriguing educational insight into your metabolic biology, but it is not a diagnostic test. Because rs1800440 carries limited penetrance and is classified as benign by clinical sequencing standards, having the AG or GG genotype does not mean you have or will develop any specific health disorder. It merely reflects a common human variation in how the CYP1B1 enzyme performs baseline metabolic reactions. No dietary overhauls, preventative surgeries, or targeted medications are indicated solely based on this variant. If you are reviewing your genetic data due to questions about hormone therapy, hair thinning, or general medication responses, it is vital to consult a qualified healthcare provider, genetic counselor, or clinical pharmacist before taking any action or changing prescribed treatment plans.
How common is this variant?
The minor G allele has an approximate frequency of 15% to 20% in populations of European ancestry (around 18% in gnomAD European non-Finnish cohorts), but is markedly less frequent in East Asian ancestries (~1%).
Frequently asked questions
What does having the rs1800440 variant mean for my health?
Having the rs1800440 variant simply means you carry a common biochemical variation that slightly modifies the CYP1B1 enzyme. It is classified as benign in clinical databases like ClinVar and does not cause genetic disease on its own. It is considered an educational trait marker rather than a diagnostic medical factor.
Does rs1800440 cause cancer?
No. While early candidate gene studies explored whether altered estrogen metabolism might influence cancer risk, large systematic reviews and meta-analyses have found no consistent or significant association between rs1800440 and cancers like colorectal cancer. The variant is not considered a causative cancer gene.
Why is rs1800440 mentioned in hair loss and frontal fibrosing alopecia research?
CYP1B1 variants, including rs1800440, have appeared in genome-wide association studies exploring polygenic susceptibility to frontal fibrosing alopecia (FFA). Researchers hypothesize that altered xenobiotic or estrogen metabolism in the skin might interact with immune system genes like HLA-B, but rs1800440 alone is neither necessary nor sufficient to cause hair loss.
Can I use my rs1800440 status to change my medications or hormone replacement?
No, you should never alter your medications or hormone therapy based on this single variant. Pharmacogenomic guidelines from bodies such as CPIC do not recommend dosing adjustments for CYP1B1 rs1800440. Any questions regarding hormone metabolism or drug safety should be reviewed with your doctor or pharmacist.
Sources & further reading
Educational information only, last refreshed 9/7/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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This variant (p.Asn453Ser, formerly Val432Leu) in the CYP1B1 gene is associated with altered enzyme activity and has been investigated for susceptibility to various cancers, including breast and prostate cancer.
This variant (p.Gly61Glu) is a well-documented pathogenic mutation associated with primary congenital glaucoma (PCG) and is also studied for its role in oxidative stress and drug response pathways.
A missense variant in CYP1B1 (p.Ala119Ser) associated with primary congenital glaucoma and juvenile open-angle glaucoma risk.
A well-characterized loss-of-function missense variant causing primary congenital glaucoma through abnormal trabecular meshwork development.
Missense variant in CYP1B1 associated with primary congenital glaucoma.
A classic founder missense mutation in CYP1B1 responsible for early-onset recessive infantile and juvenile glaucoma.