CYP17A1 rs121908080: Understanding Rare Genetic Variants
The rs121908080 variant is a rare genetic change located within the CYP17A1 gene. It is associated with a condition known as combined 17-alpha-hydroxylase/17,20-lyase deficiency, which affects the body's ability to produce essential steroid hormones.
What each genotype means
Typical enzyme activity
This genotype represents the most common, expected sequence for the CYP17A1 gene. Individuals with this profile typically maintain normal 17-alpha-hydroxylase and 17,20-lyase enzyme function, which is essential for the production of cortisol and sex steroids.
This is the wild-type or common genotype found in the vast majority of the global population.
Carrier of rare variant
This genotype indicates you carry one copy of the rare variant rs121908080. Because this condition is typically inherited in an autosomal recessive pattern, carriers generally do not exhibit the clinical symptoms of 17-alpha-hydroxylase/17,20-lyase deficiency, though you should consult a genetic counselor regarding family planning.
This specific genotype is extremely rare, with the variant allele occurring at a frequency of less than 0.00005 in global populations.
Potential enzyme deficiency
This genotype indicates the presence of two copies of the rare variant, which is associated with 17-alpha-hydroxylase/17,20-lyase deficiency. This condition can lead to clinical features such as hypertension, hypokalemia, and impaired sexual development due to disrupted steroid hormone synthesis; please discuss these findings with an endocrinologist or medical geneticist.
This homozygous genotype is exceptionally rare and is not expected to be found in the general population at any significant frequency.
What is the rs121908080 Variant?
The rs121908080 variant is a specific alteration in the DNA sequence of the CYP17A1 gene. In genetics, an rsID (reference SNP cluster ID) acts as a unique identifier for a specific location in the human genome. This particular variant is categorized as a loss-of-function mutation, meaning it disrupts the normal instructions the gene provides to the cell. Located on chromosome 10, the CYP17A1 gene provides the blueprint for an enzyme that is critical for the synthesis of various hormones. Because this variant is extremely rare, it is not typically found in the general population. Geneticists study such variants to understand how specific changes in our DNA can lead to differences in biological function, particularly in the complex pathways that regulate hormone production throughout the body.
The Role of the CYP17A1 Gene
The CYP17A1 gene encodes an enzyme known as cytochrome P450 17A1. This enzyme is a vital component of the steroidogenic pathway, which takes place primarily in the adrenal glands and the gonads (testes and ovaries). The enzyme performs two distinct chemical reactions: 17-alpha-hydroxylase activity and 17,20-lyase activity. These reactions are essential for the production of cortisol, a hormone that helps the body respond to stress, as well as sex steroids like androgens and estrogens. When the CYP17A1 gene functions correctly, it ensures that the body maintains a delicate balance of these hormones. If the gene is altered, as is the case with certain pathogenic variants, the enzyme may fail to perform these reactions, leading to a deficiency in the hormones that rely on this pathway for their synthesis.
Research and Clinical Associations
Scientific research has linked loss-of-function mutations in the CYP17A1 gene to a rare form of Congenital Adrenal Hyperplasia (CAH) known as 17-alpha-hydroxylase/17,20-lyase deficiency. This condition is inherited in an autosomal recessive pattern, meaning an individual typically needs to inherit two copies of a pathogenic variant—one from each parent—to experience the clinical symptoms. Clinical presentations associated with this deficiency can include hypertension, hypokalemia, and differences in sexual development. Because the enzyme is required for the production of sex steroids, individuals with this deficiency may experience challenges with puberty and fertility. The evidence linking specific CYP17A1 mutations to these clinical outcomes is considered strong in the context of medical genetics, as the biochemical pathway affected is well-documented in peer-reviewed literature.
Population Frequency and Prevalence
The rs121908080 variant is classified as extremely rare. According to data from the Genome Aggregation Database (gnomAD), the frequency of this variant is less than 0.00005. This means that the variant is found in a very small fraction of the individuals sequenced in large-scale genomic studies. Because it is so uncommon, it is not a variant that the general public would typically encounter or carry. Its rarity is consistent with many pathogenic variants that cause recessive conditions, as these mutations are often kept at very low levels in the human gene pool. Researchers use these frequency statistics to help determine the likelihood that a specific variant is the cause of a rare clinical condition in a patient.
Interpreting Genetic Information
It is important to understand that identifying a rare variant like rs121908080 does not constitute a medical diagnosis. Genetic information is complex, and the presence of a variant does not always guarantee that an individual will develop a specific condition, especially if they only carry one copy of a recessive mutation. If you have received information about this variant from a genetic test, it is essential to consult with a qualified healthcare provider or a genetic counselor. They can help interpret the results in the context of your personal and family medical history. Never use genetic data to make decisions about your health or to change any prescribed medications without first discussing the information with your clinician or pharmacist.
How common is this variant?
The rs121908080 variant is extremely rare, with a frequency of less than 0.00005 in the gnomAD database across all major ancestral populations.
Frequently asked questions
What is 17-alpha-hydroxylase deficiency?
It is a rare genetic disorder caused by mutations in the CYP17A1 gene. It prevents the body from producing enough cortisol and sex hormones, which can lead to symptoms like high blood pressure and issues with sexual development.
Is rs121908080 common?
No, this variant is extremely rare. It is found in fewer than 0.00005% of the population, making it very unlikely to be present in the average person.
Can I be tested for this variant?
Yes, this variant can be identified through clinical genetic testing. If you are concerned about your risk for genetic conditions, you should speak with a doctor or a genetic counselor.
What should I do if I have this variant?
If you have been identified as a carrier or have two copies of this variant, you should discuss the results with a medical professional. They can provide context based on your health history and explain what it means for you.
Sources & further reading
Educational information only, last refreshed 9/23/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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Pathogenic variant in CYP17A1 causing 17-alpha-hydroxylase deficiency, ambiguous genitalia, and hypergonadotropic hypogonadism.
Pathogenic nucleotide change in CYP17A1 disrupting sex steroid synthesis, causing amenorrhea and hypertension in adolescent females.