CYP21A2 rs104894332: Genetic Causes of Non-Classic CAH
The rs104894332 variant is a well-characterized missense alteration in the CYP21A2 gene, also documented in the scientific literature as p.Pro30Leu (c.89C>T). This variant reduces the enzymatic activity of steroid 21-hydroxylase and is primarily associated with non-classic congenital adrenal hyperplasia (NC-CAH) and associated hyperandrogenic symptoms such as female subfertility. Because congenital adrenal hyperplasia is an autosomal recessive condition, clinical manifestations typically depend on the genetic status of both copies of the CYP21A2 gene.
What each genotype means
Typical 21-hydroxylase function
You carry two copies of the standard reference allele for this position in the CYP21A2 gene. Research shows normal steroid 21-hydroxylase enzymatic activity, with no increased genetic risk for non-classic congenital adrenal hyperplasia related to this specific variant. Your body is expected to maintain baseline cortisol and androgen biosynthesis pathways through this locus.
Carried by approximately 97% to 98% of individuals of European and Ashkenazi ancestry, and by over 99% of individuals across most other global populations.
Carrier of non-classic CAH
You carry one copy of the p.Pro30Leu missense variant associated with mild to moderate 21-hydroxylase deficiency. Heterozygous carriers typically do not experience classic symptoms, though some published studies observe subtle androgenic variations or mild subfertility in females. Carrier status carries reproductive relevance if a partner also harbors a pathogenic CYP21A2 variant.
Carried by roughly 1 in 30 to 1 in 50 individuals in European and Ashkenazi Jewish populations, but it is considerably less common in East Asian and African ancestries.
Non-classic congenital adrenal hyperplasia
You carry two copies of the pathogenic p.Pro30Leu variant, which retains approximately 30% to 50% of normal 21-hydroxylase activity. This genotype is statistically linked to non-classic congenital adrenal hyperplasia (NC-CAH), which may manifest as late-onset hyperandrogenism, irregular menses, acne, or reduced fertility, though some homozygous individuals remain asymptomatic. Any evaluation or hormone-related management should be discussed with an endocrinologist.
Very rare across global populations, occurring in fewer than 1 in 4,000 individuals, with slightly higher incidence in enriched founder populations like Ashkenazi Jewish cohorts.
Variant Details and Genomic Context
The single nucleotide polymorphism rs104894332 represents a cytosine-to-thymine substitution in the human CYP21A2 gene, resulting in the exchange of proline for leucine at amino acid position 30 (p.Pro30Leu). The CYP21A2 gene is located on chromosome 6 within the major histocompatibility complex (HLA) region. This genomic locus, termed the RCCX module, is extraordinarily complex due to tandem duplications and the presence of a non-functional pseudogene, CYP21A1P, which shares roughly 98% sequence homology with CYP21A2. The proximity of the active gene to this pseudogene predisposes the locus to frequent unequal crossing-over events and intergenic recombinations. The rs104894332 missense change is one of several classic point mutations historically transferred from the inactive pseudogene to the functional gene sequence, altering the protein structure of steroid 21-hydroxylase.
Biological Function of the CYP21A2 Enzyme
The CYP21A2 gene encodes the microsomal cytochrome P450 enzyme 21-hydroxylase, which plays an essential role in adrenal steroidogenesis. In the adrenal cortex, this enzyme catalyzes the conversion of progesterone into 11-deoxycorticosterone and 17-hydroxyprogesterone into 11-deoxycortisol, critical precursor steps required for the synthesis of aldosterone and cortisol. When 21-hydroxylase activity is partially impaired—as is typical with the p.Pro30Leu substitution—the adrenal glands cannot synthesize cortisol at optimal efficiency. This partial enzymatic block prompts the pituitary gland to increase adrenocorticotropic hormone (ACTH) secretion to compensate. The sustained trophic drive causes adrenal cortical hyperplasia and redirects accumulated steroid precursors down intact androgenic pathways, resulting in excessive production of adrenal androgens.
Phenotypic Associations and Evidence Strength
Decades of clinical endocrinology research have established rs104894332 as a definitive pathogenic variant in autosomal recessive 21-hydroxylase deficiency. In functional assays, the p.Pro30Leu substitution retains partial enzymatic activity, which generally places it in the 'mild' or non-classic congenital adrenal hyperplasia (NC-CAH) category. Individuals carrying this variant in trans with another pathogenic CYP21A2 variant or in a homozygous state frequently manifest milder, late-onset hyperandrogenic symptoms. In biological females, this androgen excess can manifest during adolescence or early adulthood as oligomenorrhea, hirsutism, severe acne, polycystic-appearing ovaries, and subfertility due to chronic anovulation. Although research firmly establishes its role in NC-CAH, clinical expressivity varies, and rare individuals carrying p.Pro30Leu alongside another severe allele have presented with simple virilizing phenotypes.
Interpreting Genetic Results and Clinical Steps
Consumer genomic profiling that identifies the rs104894332 variant should not be mistaken for a formal medical diagnosis. Because 21-hydroxylase deficiency is inherited in an autosomal recessive manner, carrying a single altered allele (heterozygosity) generally renders an individual an asymptomatic carrier, although some studies suggest minor baseline shifts in hormone metabolites. Furthermore, high-throughput consumer microarrays and standard short-read sequencing platforms are notorious for misidentifying variants in CYP21A2 due to interference from the CYP21A1P pseudogene. Definitive diagnostic testing requires specialized molecular methodologies—such as multiplex ligation-dependent probe amplification (MLPA) or long-read sequencing—paired with baseline or ACTH-stimulated serum 17-hydroxyprogesterone measurements evaluated by a medical geneticist or endocrinologist.
How common is this variant?
The rs104894332 alternative allele is present at an estimated frequency of approximately 0.015 (1.5%) in European and Ashkenazi Jewish populations, while remaining rarer in many East Asian and African populations.
Frequently asked questions
What is the difference between classic and non-classic CAH?
Classic congenital adrenal hyperplasia involves severe enzyme impairment, often leading to critical neonatal salt-wasting crises and prenatal genital ambiguity in females. Non-classic CAH involves partial enzyme activity, typically causing milder symptoms of androgen excess that emerge later in life during puberty or adulthood.
Does carrying one copy of rs104894332 mean I have a hormonal disorder?
No, carrying a single T allele normally makes you a carrier because non-classic CAH follows an autosomal recessive inheritance pattern. Most carriers remain completely asymptomatic, although clinical manifestations can occur if a second variant is inherited on the other chromosome.
Why is genetic testing for the CYP21A2 gene uniquely difficult?
CYP21A2 sits directly beside a nearly identical pseudogene named CYP21A1P on chromosome 6. Standard consumer genotyping and short-read sequencing often struggle to distinguish between the two sequences, requiring clinical-grade specialized assays like MLPA to yield accurate results.
How does this variant affect female fertility?
When present in both copies or combined with another pathogenic CYP21A2 allele, the partial enzyme deficiency can lead to elevated adrenal androgens. These excess androgens can interfere with regular ovulation and menstrual regularity, potentially reducing fertility unless medically evaluated and managed.
Sources & further reading
Educational information only, last refreshed 9/12/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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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.
This variant in the CYP21A2 gene is involved in steroid hormone metabolism and is noted in clinical databases.
This variant is classified as pathogenic and is associated with 21-hydroxylase deficiency.