Test Overview
Test Methodology

The coding exons and associated, adjacent consensus splice sites of the PHOX2B gene are amplified using specific sets of primer pairs, and bidirectionally sequenced using fluorescently labeled chain-terminating dideoxynucleotides incorporation method (Sanger sequencing).

Test Usage

Analysis for the presence of pathogenic variants in PHOX2B gene (MIM: 603851) in patients with a phenotype consistent with congenital central hypoventilation syndrome (CCHS) (MIM: 209880; https://www.ncbi.nlm.nih.gov/books/NBK1427/) or neuroblastoma (with Hirschsprung disease) (NBLST2) (MIM: 613013). Sanger sequencing can detect the two major categories of PHOX2B germline variants causing CCHS or neuroblastoma: polyalanine repeat expansion mutations (PARMs, p.Ala241[24_33], 90–92%) in exon 3 polyalanine region, and non-polyalanine repeat expansion mutations (NPARMs, 8–10%) in other regions.

Reference Range *

Interpretive report provided.

* Reference ranges may change over time. Please refer to the original patient report when evaluating results.

Test Limitations

Sanger sequencing will not identify variants in the regulatory elements or deep intronic regions of the PHOX2B gene, and cannot detect variants in other genes associated with the clinical diagnosis. Sanger sequencing will not detect large deletions, duplications or rearrangements involving PHOX2B; specifically, it will not identify the whole gene or exon 3 deletion, a rare mechanism (<1%) for CCHS. Somatic/germline mosaicism is present in 5%-25% of asymptomatic parents, and Sanger sequencing cannot reliably detect somatic mosaicism less than 20%.

Test Details
Days Set Up
Monday - Friday
Analytic Time

10 days

Soft Order Code
PX2BS
MiChart Code
PHOX2B Gene Sequencing
Synonyms
    Laboratory
    MMGL
    Section
    MMGL Molecular Genetics
    Specimen Requirements
    Collection Instructions

    Restricted to Michigan Medicine in-patient orders only.

    Alternate Specimen
    Cheek swab kit (Oragene OCD-100), follow collection instructions.
    Saliva kit (Oragene OGD-510), follow collection instructions.
    Contraindications
    PHOX2B gene sequencing should not be ordered for phenotypically normal individuals.
    Normal Volume
    5 mL whole blood
    Minimum Volume
    1 mL whole blood (0.5 mL infants)
    Storage Temperature
    Storage Temperature:
    Room temperature up to 24 hours or 2-8°C up to 5 days for blood
    2-36°C for saliva
    Rejection Criteria
    Hemolyzed blood sample. Fresh tissue (POC) or paraffin embedded specimens are not acceptable.
    Additional Information

    Most insurance carriers require prior authorization for genetic testing. Testing will not begin until insurance prior authorization is received by the laboratory or it is confirmed that prior authorization is not required. The ordering health care provider can obtain the prior authorization or request the laboratory to submit it. To obtain BCN prior authorization call Joint Venture Hospital Laboratories (JVHL) at 800-445-4979; for all other insurances, contact the plan directly. By ordering this test the clinician acknowledges that informed consent, https://mlabs.umich.edu/sites/default/files/2023-04/file/germline-conse…, has been obtained from the patient as required by applicable state or federal laws and the ordering clinician has authorization from the patient permitting MLabs to report the test results to the ordering clinician. Test includes medical geneticist interpretation of results billed as a separate additional charge. This test is not available without interpretation.

    Billing
    CPT Code
    81404
    Fee Code
    DA176
    Pro Fee CPT
    G0452-26
    NY State Approved
    No