Congenital adrenal hyperplasia due to 17α-hydroxylase deficiency

Congenital adrenal hyperplasia due to 17α-hydroxylase deficiency
Synonyms	17α-hydroxylase/17,20-lyase deficiency, CYP17A1 deficiency
Pronounce	N/A
Specialty	N/A
Symptoms	Hypertension, hypokalemia, delayed puberty, sexual infantilism, primary amenorrhea, ambiguous genitalia
Complications	Infertility, adrenal hyperplasia, sexual development disorders, osteoporosis
Onset	At birth or puberty
Duration	Lifelong
Types	Complete or partial
Causes	Mutation in CYP17A1 gene (encoding 17α-hydroxylase)
Risks	Consanguinity, family history
Diagnosis	Serum hormone tests, karyotyping, genetic testing
Differential diagnosis	Androgen insensitivity syndrome, other CAH types, gonadal dysgenesis
Prevention	Genetic counseling
Treatment	Glucocorticoid replacement, mineralocorticoid receptor antagonists, sex hormone therapy
Medication	Hydrocortisone, fludrocortisone, spironolactone, estrogen/testosterone
Prognosis	Good with treatment; requires lifelong hormone therapy
Frequency	Rare (1 in 1,000,000)
Deaths	Rare with appropriate treatment

Congenital adrenal hyperplasia due to 17α-hydroxylase deficiency is a rare form of congenital adrenal hyperplasia (CAH), caused by mutations in the CYP17A1 gene. This gene encodes the enzyme 17α-hydroxylase/17,20-lyase, which is critical for the biosynthesis of both glucocorticoids and sex steroids in the adrenal gland and gonads.

Genetic Basis

This condition is inherited in an autosomal recessive manner. Mutations in the CYP17A1 gene impair the function of the 17α-hydroxylase enzyme, blocking the conversion of pregnenolone and progesterone to their 17α-hydroxylated forms. This results in reduced production of both cortisol and sex hormones, and excess production of mineralocorticoids, particularly deoxycorticosterone and corticosterone.

Pathophysiology

17α-hydroxylase converts pregnenolone and progesterone to their 17α-hydroxy forms. It corresponds to the red arrows in this reaction scheme.

Deficiency of 17α-hydroxylase leads to:

• Impaired production of cortisol, leading to increased ACTH secretion and adrenal hyperplasia.
• Deficient synthesis of androgens and estrogens, causing underdeveloped or ambiguous genitalia and lack of secondary sexual characteristics.
• Increased production of mineralocorticoids (e.g., deoxycorticosterone), resulting in hypertension and hypokalemia.

Clinical Features

In 46,XY individuals (genetic males)

• Ambiguous genitalia
• Undescended testes
• Lack of virilization at puberty
• Infertility

In 46,XX individuals (genetic females)

• Primary amenorrhea
• Delayed puberty
• Sexual infantilism
• May appear phenotypically normal at birth, but puberty fails to progress

General symptoms in both sexes

• Hypertension
• Hypokalemia
• Fatigue
• Headaches
• Metabolic alkalosis

Diagnosis

Diagnosis involves a combination of clinical features, laboratory testing, and genetic analysis.

Laboratory findings

• Low cortisol
• Low testosterone and estradiol
• Low DHEA and androstenedione
• High ACTH
• High aldosterone precursors (e.g., deoxycorticosterone)
• Elevated progesterone and corticosterone
• Low renin activity

Genetic testing

• Identification of mutations in the CYP17A1 gene confirms the diagnosis.

Imaging

• Pelvic ultrasound or MRI may be used to assess internal genital structures and adrenal size.

Management

Hormonal replacement

• Glucocorticoids (e.g., hydrocortisone) are used to suppress ACTH and reduce adrenal hyperplasia.
• Mineralocorticoid receptor antagonists (e.g., spironolactone) may be used to control hypertension.
• Sex hormone replacement:
  • Estrogen therapy in 46,XX individuals to induce secondary sexual characteristics.
  • Testosterone therapy in 46,XY individuals depending on gender identity and desired development.

Surgical intervention

• May be considered for correction of ambiguous genitalia based on individual needs and gender assignment.

Fertility

• Infertility is common due to gonadal dysfunction. Reproductive options may be discussed with specialists.

Prognosis

With appropriate hormonal therapy and monitoring, patients can lead healthy lives. However, complications like osteoporosis, infertility, and psychosocial challenges may arise without early diagnosis and treatment.

Epidemiology

This condition is extremely rare, accounting for less than 1% of all CAH cases, with an estimated frequency of 1 in 1,000,000 births. It may be more prevalent in certain populations due to founder effects or consanguinity.

See Also

• Congenital adrenal hyperplasia
• CYP17A1
• Adrenal gland
• Endocrinology
• Ambiguous genitalia
• Hyperaldosteronism
• Hypogonadism
• Autosomal recessive inheritance