rs104894141 — CYP17A1 W17X

Rare pathogenic nonsense variant in CYP17A1 causing complete abolition of 17α-hydroxylase/17,20-lyase activity; homozygotes develop the full 17α-hydroxylase deficiency phenotype (hypertension, hypokalemia, absent puberty, low cortisol), while heterozygous carriers are clinically unaffected but carry a CYP17A1 loss-of-function allele relevant to reproductive planning.

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CYP17A1 W17X — A Premature Stop That Halts Steroid Synthesis at the First Step

The human body's ability to make cortisol, estrogens, and androgens all runs through a single enzymatic checkpoint: CYP17A1, or cytochrome P450 17α-hydroxylase/17,20-lyase11 CYP17A1, or cytochrome P450 17α-hydroxylase/17,20-lyase
A bifunctional enzyme in the adrenal cortex and gonads that performs two sequential reactions essential for cortisol and sex steroid biosynthesis. Losing either activity disrupts the entire hormonal cascade downstream. The rs104894141 variant introduces a premature stop codon at the very beginning of this protein — position 17 out of 508 amino acids — leaving the cell with essentially no functional enzyme at all. The result, when two defective alleles are inherited, is 17α-hydroxylase deficiency (17OHD)22 17α-hydroxylase deficiency (17OHD)
Also called congenital adrenal hyperplasia due to CYP17A1 deficiency, OMIM #202110. A rare autosomal recessive disorder accounting for ~1% of CAH cases, with an estimated incidence of approximately 1 in 50,000 births: the distinctive syndrome of hypertension, low potassium, and absent pubertal development.

The W17X variant was first documented in a Japanese patient33 documented in a Japanese patient
Suzuki et al., J Clin Endocrinol Metab, 1998. The patient had a 46,XY karyotype, completely female external genitalia, absent pubertal development, and hypertension — the classic presentation of complete combined 17α-hydroxylase/17,20-lyase deficiency with a 46,XY karyotype presenting with female external genitalia, absent pubertal development, and hypertension. The variant was found in compound heterozygosity with a second mutation (IVS2+5G→T, a splice-donor disruption). This pattern — compound heterozygosity with two distinct CYP17A1 loss-of-function alleles — is the most common genetic architecture for clinical 17OHD.

The Mechanism

CYP17A1 performs two consecutive reactions in steroid biosynthesis. First, 17α-hydroxylation44 17α-hydroxylation
Converts pregnenolone → 17α-hydroxypregnenolone and progesterone → 17α-hydroxyprogesterone; these are the required precursors for cortisol production in the adrenal cortex's zona fasciculata. Second, 17,20-lyase activity55 17,20-lyase activity
Cleaves the C17–C20 bond, generating DHEA and androstenedione — the entry points into the sex steroid synthesis pathway for both estrogens and androgens in gonads and adrenals.

The W17X mutation (c.51G>A on the coding strand, plus-strand C>T at chr10:102837311) creates a stop codon at amino acid position 17 — just 16 residues into the protein, before any of the functional domains (heme-binding, substrate-binding, electron transfer) are even assembled. The resulting truncated peptide is non-functional and almost certainly degraded by nonsense-mediated mRNA decay. With no CYP17A1 activity, steroidogenesis is entirely shunted away from cortisol and sex steroids. Pregnenolone and progesterone accumulate and are instead converted to deoxycorticosterone (DOC)66 deoxycorticosterone (DOC)
A potent mineralocorticoid — the second most active naturally occurring mineralocorticoid after aldosterone. DOC excess causes sodium retention, fluid overload, hypertension, hypokalemia, and suppressed renin and aldosterone through the zona glomerulosa pathway. Low cortisol drives ACTH up, which amplifies DOC production further. The gonads, meanwhile, cannot produce testosterone or estradiol — causing complete sexual infantilism regardless of chromosomal sex.

The Evidence

A large meta-analysis of 465 patients77 meta-analysis of 465 patients
Willemsen et al., J Clin Endocrinol Metab, 2025 — 178 case reports and cohort studies from 1988–2022 documents the natural history of 17OHD in detail. Hypertension was present in 57% of patients at diagnosis, hypokalemia in 45%, primary amenorrhea in 38%, and disordered sexual development in 59.5%. Mean age at diagnosis was 19.0 years. Phenotypic sex was female in 90.8% despite chromosomal sex being XY in 52.5% of the cohort — reflecting the complete feminization of XY individuals when sex steroid synthesis is absent.

The broad phenotypic spectrum88 broad phenotypic spectrum
Sun et al., Eur J Endocrinol, 2021 — 8 patients with 17OHD, including two with unexpectedly preserved cortisol synthesis despite absent sex steroids of 17OHD has been increasingly recognized. Null/null genotypes (two stop codons or frameshift mutations, like W17X compound heterozygous) consistently produce the complete phenotype. Urinary steroid metabolite profiling by mass spectrometry effectively predicts disease severity and can guide diagnosis before genetic results are available.

One important diagnostic pitfall: the mineralocorticoid-excess pattern (hypertension, hypokalemia, suppressed renin, elevated DOC) closely mimics primary aldosteronism99 primary aldosteronism
Akkus, Endocr Metab Immune Disord Drug Targets, 2023 — two 17OHD patients misdiagnosed as primary aldosteronism until adrenal imaging, gonadotropin levels, and genetic testing revealed the correct diagnosis. The distinguishing feature is hypogonadism: primary aldosteronism does not cause absent puberty or sexual infantilism.

Practical Actions

For homozygous or compound heterozygous individuals (TT or, in compound het patients, CT with another loss-of-function allele on the opposite chromosome), the diagnosis of 17OHD requires lifelong hormonal management: glucocorticoid replacement to suppress ACTH (and thereby DOC excess), sex hormone replacement to induce and maintain secondary sexual characteristics, and monitoring of blood pressure and potassium.

For heterozygous carriers (CT), no clinical syndrome results — one functional allele is sufficient for adequate steroidogenesis. Carrier status is relevant for reproductive planning: two carriers have a 25% chance of producing an affected child.

Interactions

The W17X variant acts as a complete loss-of-function allele. Its clinical expression depends on the second allele: compound heterozygosity with any other CYP17A1 null allele (frameshift, stop, splice-disrupting) produces the complete 17OHD phenotype identical to W17X homozygosity. Compound heterozygosity with a partial loss-of-function missense allele can produce partial 17OHD, with residual enzyme activity and a milder, often female-predominant presentation (recurrent ovarian cysts, oligomenorrhea, partial breast development in 46,XX individuals; variable phenotypes in 46,XY).

Other CYP17A1 pathogenic variants in the GeneOps database — including rs104894135 (Ser106Pro), rs104894137, rs104894138, and rs104894143 — cause the same enzyme deficiency through different molecular mechanisms. The disease phenotype when any two loss-of-function CYP17A1 alleles are combined is clinically equivalent regardless of which specific variants are involved.

Genotype Interpretations

What each possible genotype means for this variant.

CC Non-carrier Normal

No W17X mutation — normal CYP17A1 at this position

You carry two copies of the normal CYP17A1 allele at this position. You do not carry the W17X stop-codon mutation. The vast majority of the global population shares this result — the T allele appears in only about 1–3 per 100,000 chromosomes globally, with a slight enrichment in East Asian populations (~3 per 100,000). Normal CYP17A1 function means your steroid biosynthesis pathway can produce cortisol and sex hormones without obstruction at this enzymatic step.

CT Carrier Carrier

Carrier of one W17X allele — unaffected but relevant for reproductive planning

The W17X variant creates a stop codon at amino acid position 17 of CYP17A1 (out of 508 total residues), producing a non-functional truncated protein. In heterozygotes, the second normal CYP17A1 allele compensates fully — the adrenal cortex and gonads produce adequate enzyme from the intact allele. Subclinical biochemical differences in heterozygotes (slightly altered ACTH-stimulated corticosterone/cortisol ratios) have been detected in research settings but are not clinically actionable.

17α-hydroxylase deficiency, when fully expressed in a homozygous or compound heterozygous state, presents with mineralocorticoid-driven hypertension, hypokalemia, and complete absence of pubertal development due to absent sex steroid synthesis. This clinical syndrome does not apply to carriers.

Partner testing becomes relevant if you and your partner both carry CYP17A1 variants: the 25% Mendelian risk applies when both parents carry any loss-of-function CYP17A1 allele, regardless of which specific variant each carries.

TT Homozygous W17X Homozygous

Two copies of W17X — complete 17α-hydroxylase/17,20-lyase deficiency

The complete combined 17α-hydroxylase/17,20-lyase deficiency phenotype arises because CYP17A1 is the essential bifunctional enzyme at the branch point of steroid biosynthesis. Without it:

Mineralocorticoid excess: Pregnenolone and progesterone accumulate and are shunted into the zona glomerulosa mineralocorticoid pathway, generating large quantities of 11-deoxycorticosterone (DOC). DOC is a potent mineralocorticoid — it causes sodium and water retention, hypertension, hypokalemia, metabolic alkalosis, and suppressed renin and aldosterone levels. The ACTH-driven overproduction of DOC continues chronically because low cortisol cannot suppress pituitary ACTH secretion. Blood pressure is often severely elevated at diagnosis.

Absent cortisol: The 17α-hydroxylation step is required to produce 17α-OHP and 17α-hydroxypregnenolone, the precursors for cortisol. Without CYP17A1, the zona fasciculata pathway stalls and cortisol production is essentially zero. Patients have functional glucocorticoid deficiency that does not manifest as crisis under basal conditions (because corticosterone, which can bind the glucocorticoid receptor weakly, partly compensates), but adrenal stress reserve is absent.

Sexual infantilism: The 17,20-lyase step is required for production of DHEA and androstenedione — the substrates for both estrogen and androgen synthesis. Without it, the gonads produce neither testosterone nor estradiol. In 46,XY individuals: absence of testosterone during fetal development causes failure of external genitalia masculinization (Müllerian inhibiting factor is still present, so Müllerian structures regress, but Wolffian duct development and virilization do not occur). These individuals typically present as phenotypically female, often with cryptorchidism. In 46,XX individuals: absent estradiol production causes primary amenorrhea, absent breast development, and prepubertal uterus.

Diagnosis timeline: 17OHD is not detected by newborn screening. Diagnosis occurs most often at puberty (~mean age 19 years in the meta-analysis), when absent secondary sexual development and hypertension trigger evaluation. A minority present in infancy with adrenal crises or ambiguous genitalia in XY individuals.

Treatment involves lifelong management across three domains: - Glucocorticoid replacement: Suppresses ACTH, reduces DOC production, and corrects the mineralocorticoid excess (blood pressure normalizes in most patients). Hydrocortisone is preferred in children (10–20 mg/m²/day divided doses); dexamethasone 0.3–0.5 mg/day or prednisone in adults. - Sex hormone replacement: Estrogen plus progestogen for 46,XX individuals and for 46,XY individuals raised female; testosterone for 46,XY individuals raised male. Induces and maintains secondary sexual characteristics and protects bone density. - Monitoring and antihypertensives: Blood pressure usually resolves with glucocorticoid replacement alone; persistent hypertension is managed with potassium-sparing diuretics or calcium channel blockers if needed.

Fertility is generally absent without assisted reproductive technology given the degree of gonadal insufficiency.