Congenital Adrenal Hyperplasia (CAH)

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Gene Symbol: CYP21A2

Chromosomal Locus: 6p21.33
Protein: Steroid 21-Hydroxylase
Pseudonyms: 21-Hydroxylase Deficiency, Cytochrome P450, family 21, subfamily A, polypeptide 2, CYP21, CYP21B, 21-OHase
TESTING METHODOLOGY: Polymerase chain reaction (PCR) and DNA sequencing of the entire coding region of the CYP21A2 gene; 10 exons including intron-exon borders.
  • Collect: Prefer two 5ml whole blood EDTA (lavender top) tube.
  • Min. Collection: 0.7 ml whole blood EDTA.
  • Transport: blood EDTA at Room Temp shipped regular next day air (No Saturday delivery; store specimen at 4°C and ship Monday).
  • Stability: Ambient: up to 7 days; Refrigerated: 2 weeks. Frozen: unacceptable
  • Unacceptable Conditions: Serum. Frozen or severely hemolyzed blood. Clotted blood.
  • Prenatal testing: Direct: 5ml direct unspun amniotic fluid or 15mg CVS tissue with a backup flask growing. Culture: confluent T25 flask. Maternal blood sample is required for maternal cell contamination studies.
A Molecular Genetics Laboratory Test Requisition must accompany the specimen. Contact the Molecular Laboratory at 918-502-1721 to obtain further information.
Note: Counseling and informed consent are recommended for genetic testing; a consent form is available as a resource but not required.
Incidence: 1/10,000 live births, carrier incidence is 1/60.
Inheritance: Autosomal Recessive. About 1% of mutations are de novo.
Disease Characteristics: CAH is most commonly caused by 21-hydroxylase deficiency. There are two forms of classic CAH; the simple virilizing form (~25%) and the salt-wasting form (75%). Newborns with salt-wasting CAH are at risk for life-threatening salt-wasting crises. The non-classic form includes postnatal hyperandrogenism and the females are not virilized at birth. Reduced fertility is displayed in all forms of the condition.
Molecular Genetic Mechanism: CAH is caused by mutations, deletions, and rearrangements in the CYP21A2 gene. Approximately 50-60% of the CAH genes have a C or A to G mutation 13bp upstream of the 3rd exon (c.293-13A>G). The most common mutational mechanism is gene conversion between an extremely homologous pseudogene (CYP21A2P).
Clinical Sensitivity: 75-90%
Analytical Sensitivity: 99%
Test Limitations: This test does not detect deletions, duplications, or rearrangements in the CYP21A1 gene. Rare diagnostic errors can occur due to primer / probe site mutations or rare polymorphisms.

  • Newborns with ambiguous genitalia.
  • To determine risks of CAH in families with clinical history of the disease.
  • To confirm a diagnosis to improve treatment options, symptoms and fertility.
  • Fetus with ambiguous sex determination ultrasound result.
Genetics Home Reference - CYP21A2: