CYP21A2 rs7755898: Understanding the Q318X Variant
The rs7755898 variant is a genetic marker associated with the Q318X mutation in the CYP21A2 gene. This specific change is linked to 21-hydroxylase deficiency, a condition that can lead to congenital adrenal hyperplasia.
What each genotype means
Typical enzyme function
This genotype represents the common, functional version of the CYP21A2 gene. It is not associated with the Q318X null mutation that causes 21-hydroxylase deficiency.
This is the most common genotype found in the general population.
Carrier of null allele
You carry one copy of the Q318X mutation, which is a null allele that results in no functional 21-hydroxylase enzyme activity. Because this condition is inherited in an autosomal recessive pattern, carriers typically do not exhibit symptoms of congenital adrenal hyperplasia, but you should discuss this result with a genetic counselor or clinician.
This genotype is rare in the general population, though frequency varies by ancestry.
Associated with adrenal deficiency
This genotype indicates the presence of two copies of the Q318X null mutation, which is associated with the salt-wasting form of congenital adrenal hyperplasia. This condition requires clinical management and monitoring by a specialist; please consult your healthcare provider for appropriate medical evaluation and guidance.
This genotype is very rare and is associated with a clinical diagnosis of 21-hydroxylase deficiency.
What is rs7755898?
The rs7755898 variant is a single nucleotide polymorphism (SNP) located on chromosome 6 within the CYP21A2 gene. In genetic research, this SNP is frequently used as a marker to identify the presence of the Q318X mutation. The Q318X mutation is a specific change in the DNA sequence that results in a premature stop codon, effectively signaling the cell to stop building the protein before it is complete. Because this mutation creates a non-functional version of the protein, it is often referred to as a null allele. Understanding the location and function of this SNP is important for researchers studying how specific genetic changes can disrupt normal biological processes. It is important to note that while this SNP serves as a marker, the actual clinical impact depends on the presence of the underlying mutation it represents.
The Role of the CYP21A2 Gene
The CYP21A2 gene provides the essential instructions for the body to produce an enzyme known as 21-hydroxylase. This enzyme belongs to the cytochrome P450 family, a group of proteins that play a critical role in the production of steroid hormones. Specifically, 21-hydroxylase is responsible for converting certain precursor molecules into cortisol and aldosterone, which are vital hormones for regulating blood pressure, metabolism, and the body's response to stress. When the CYP21A2 gene is mutated, the production of this enzyme can be significantly reduced or completely absent. This deficiency disrupts the normal pathway of hormone synthesis, leading to an imbalance in steroid levels. The severity of the resulting health condition often correlates with how much functional enzyme the body is still able to produce.
Research and Clinical Associations
Scientific literature associates the Q318X mutation, marked by rs7755898, with 21-hydroxylase deficiency, which is the primary cause of congenital adrenal hyperplasia. Individuals who inherit two copies of this null allele—one from each parent—may experience the most severe form of the condition, known as the salt-wasting form. In this state, the body cannot produce sufficient aldosterone, leading to a dangerous loss of salt and water. The evidence linking this specific genetic marker to the condition is considered strong in clinical genetics, as it directly impacts the protein's ability to function. However, genetic testing for this gene is complex due to the presence of a highly similar pseudogene nearby, which can sometimes lead to misinterpretations or technical challenges during analysis. Consequently, clinical diagnosis requires specialized molecular testing to ensure accuracy.
Interpreting Your Genetic Information
If you encounter this variant in a genetic report, it is essential to understand that direct-to-consumer testing can sometimes produce inaccurate results for this specific gene. Some studies have noted discrepancies where individuals were identified as carriers, but further clinical validation was required to confirm the finding. Because of the complexity of the CYP21A2 gene, you should never use this information to make medical decisions or assume a diagnosis. If you are concerned about your genetic status or family history, the most appropriate step is to consult with a healthcare provider or a genetic counselor. They can order validated clinical-grade testing and help you interpret the results in the context of your overall health. Always discuss any findings with a professional who can provide personalized guidance and appropriate follow-up care.
How common is this variant?
The rs7755898 variant is considered rare in the general population. Due to the complexity of the CYP21A2 gene region, frequency data can vary significantly between different genetic databases.
Frequently asked questions
What is 21-hydroxylase deficiency?
21-hydroxylase deficiency is a genetic condition that affects the production of essential hormones like cortisol and aldosterone. It is the most common cause of congenital adrenal hyperplasia.
Is rs7755898 a reliable marker for congenital adrenal hyperplasia?
While it is a known marker for the Q318X mutation, technical challenges in testing this gene mean that results should always be verified by a clinical laboratory. Do not rely on consumer-grade reports for a medical diagnosis.
What should I do if my report shows the T allele?
If your report indicates the presence of the T allele, you should discuss these results with your doctor or a genetic counselor. They can determine if follow-up clinical testing is necessary.
Can I be a carrier without having symptoms?
Yes, individuals who are carriers of a single copy of a recessive mutation typically do not show symptoms of the condition. However, it is important to speak with a professional to understand your specific genetic status.
Sources & further reading
Educational information only, last refreshed 9/18/2026. Not medical advice — these associations describe population statistics, not individual predictions.
Curious what your genotype is for rs7755898?
Upload a raw DNA file from 23andMe, AncestryDNA, MyHeritage, or FamilyTreeDNA and see this variant — plus thousands more — interpreted in your full report.
Get my report — $29Related variants in CYP21A2
Pathogenic variant (p.Val282Leu) in CYP21A2 associated with non-classic congenital adrenal hyperplasia.
Pathogenic variant associated with non-classic congenital adrenal hyperplasia presenting with hyperandrogenism, oligomenorrhea, and subfertility.
Pathogenic variant in CYP21A2 associated with 21-hydroxylase deficiency, used in reproductive carrier screening.
Pathogenic missense variant in CYP21A2 associated with 21-hydroxylase deficiency, a cause of congenital adrenal hyperplasia.
Well-characterized pathogenic missense variant (p.Pro30Leu) causing non-classic congenital adrenal hyperplasia and female hyperandrogenic subfertility.
This variant in the CYP21A2 gene is involved in steroid hormone metabolism and is noted in clinical databases.