Congenital adrenal hyperplasia (CAH) is a group of inherited conditions caused by variants in several enzymes involved in the synthesis of cortisol in the adrenal glands. In this "Test in Focus" episode of the "Answers From the Lab" podcast, Michelle Kluge, MS, CGC, discusses how Mayo Clinic Laboratories' CYPZ test can accurately identify both carriers and individuals who are clinically affected by the most common form of CAH.

"At least 90% of CAH cases are caused by variants in the CYP21A2 gene, which is notorious for being difficult to interrogate," Kluge says. "It has high homology with a nearby pseudogene, and so is difficult to capture by routine genetic testing."

Several laboratories now offer genotyping for common pathogenic variants of CYP21A2 on their carrier screening panels. However, Mayo Clinic Laboratories increasingly receives requests for its CYPZ test as a follow-up, due to conflicting or confusing carrier screening results from external laboratories.

Mayo Clinic Laboratories uses Sanger sequencing to perform molecular genetic testing of CYP21A2. The methodology helps avoid the limitations of standard next-generation sequencing assays of highly homologous regions.

"Our approach allows us to quote a detection rate of greater than 99% for patients with a clinical diagnosis of 21-hydroxylase deficient CAH," Kluge says. "In some cases, this methodology allows us to provide patients with additional phasing information and a more in-depth report."

Listen to learn more about how the CYPZ test can provide accurate, in-depth results for carriers and individuals affected by CAH.

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Testing

CYPZ    | 21-Hydroxylase Gene, CYP21A2, Full Gene Analysis, Varies

Useful information

• Carrier screening and diagnosis of 21-hydroxylase deficient CAH in individuals with a personal or family history of 21-hydroxylase deficiency, or as follow-up to positive CAH newborn screens and/or measurement of basal and adrenocorticotropic hormone- 1-24 stimulated 17-hydroxyprogesterone, androstenedione, and other adrenal steroid levels.
• May be used to identify CYP21A2 variant in individuals with a suspected diagnosis of 21-hydroxylase deficient CAH when a common variant panel is negative or only identifies 1 variant.
• May be used in prenatal cases of ambiguous genitalia detected by ultrasound, particularly when the fetus is confirmed XX female by chromosome analysis.
• This test should also be used for known/familial variant analysis for CYP21A2. Due to the complexity of the CYP21A2 locus, site-specific testing for known/familial variants is not offered for this gene.

Specimen requirements

Submit only 1 of the following specimens:

• Specimen Type: Whole blood
• Container/Tube:
• Preferred: Lavender top (EDTA)
• Specimen Volume: 3 mL

Collection Instructions:

• Invert several times to mix blood.
• Send specimen in original tube. Do not aliquot.
  • Specimen Stability Information: Ambient (preferred) 4 days/Refrigerated 14 days

Prenatal Specimens

• Specimen Type: Amniotic fluid
• Container/Tube: Amniotic fluid container
• Specimen Volume: 20 mL
• Specimen Stability Information: Refrigerated (preferred)/Ambient
• Specimen Type: Chorionic villi
• Container/Tube: 15-mL tube containing 15 mL of transport media
• Specimen Volume: 20 mg
• Specimen Stability Information: Refrigerated

Acceptable

• Specimen Type: Confluent cultured cells
• Container/Tube: T-25 flask
• Specimen Volume: 2 Flasks
• Collection Instructions: Submit confluent cultured cells from another laboratory.
• Specimen Stability Information: Ambient (preferred)/Refrigerated

Performance information

• Analytic time: 14 to 21 days
• Day(s) and time(s) performed: Varies

Case study

Monozygotic twins discordant for congenital adrenal hyperplasia due to mosaicism

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