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HelpTest Code NCYB Recessive Congenital Methemoglobinemia, CYB5 and CYB5 Reductase Genetic Analysis, Next-Generation Sequencing, Varies
Ordering Guidance
This test should be performed after more common causes of methemoglobinemia have been eliminated. To assess for more common causes of methemoglobinemia, order MEV1 / Methemoglobinemia Evaluation, Blood.
Testing for the CYB5A and CYB5R3 genes as part of a customized panel is available. For more information see CGPH / Custom Gene Panel, Hereditary, Next-Generation Sequencing, Varies.
Multiple gene panels are available. For more information see NHEP and Subpanel Comparison Gene List.
Targeted testing for familial variants (also called site-specific or known variants testing) is available for the CYB5A and CYB5R3 genes. See FMTT / Familial Variant, Targeted Testing, Varies. To obtain more information about this testing option, call 800-533-1710.
Additional Testing Requirements
This test is best interpreted in the context of protein functional findings by enzymatic assay and complete blood cell count analysis. This complete interpretation can be provided by also ordering the MEV1 / Methemoglobinemia Evaluation, Blood. Fill out the information sheet and indicate that a next-generation sequencing test was also ordered. Providing complete blood cell count data and clinical notes will also allow more precise interpretation of results.
Shipping Instructions
Specimen preferred to arrive within 96 hours of collection.
Necessary Information
1. Metabolic Hematology Next-Generation Sequencing (NGS) Patient Information is required. Testing may proceed without the patient information; however, the information aids in providing a more thorough interpretation. Ordering providers are strongly encouraged to fill out the form and send with the specimen.
2. If form not provided, include the following information with the test request: clinical diagnosis, pertinent clinical history (ie, complete blood cell count results and relevant clinical notes), and differentials based on clinical presentation and/or laboratory findings.
Specimen Required
Specimen Type: Whole blood
Patient Preparation: A previous bone marrow transplant from an allogenic donor will interfere with testing. Call 800-533-1710 for instructions for testing patients who have received a bone marrow transplant.
Container/Tube:
Preferred: Lavender top (EDTA)
Acceptable: Yellow top (ACD)
Specimen Volume: 3 mL
Collection Instructions:
1. Invert several times to mix blood.
2. Send whole blood specimen in original tube. Do not aliquot.
Specimen Stability Information: Ambient (preferred) 4 days/Refrigerated
Forms
1. Metabolic Hematology Next-Generation Sequencing (NGS) Patient Information (T816) is required.
2. New York Clients-Informed consent is required. Document on the request form or electronic order that a copy is on file. The following documents are available.
-Informed Consent for Genetic Testing (T576)
-Informed Consent for Genetic Testing (Spanish) (T826)
3. If not ordering electronically, complete, print, and send a Benign Hematology Test Request (T755) with the specimen.
Secondary ID
618977Useful For
Providing a genetic evaluation for patients with a personal or family history suggestive of recessive congenital methemoglobinemia
Genotype confirmation of borderline cytochrome b5 reductase (methemoglobin reductase: METR) enzyme activity levels
Identifying variants within the CYB5 and CYB5 reductase genes (CYB5A, CYB5R3) allowing for further genetic counseling
Testing Algorithm
Genetic testing for congenital methemoglobinemia is indicated if:
-There is cyanosis in the setting of clinically stable patient ("more blue than sick")
-Methemoglobin reductase (cytochrome b5 reductase) activity is decreased
-Hemoglobin electrophoresis, particularly high-performance liquid chromatography testing, is negative
Special Instructions
Method Name
Sequence Capture and Targeted Next-Generation Sequencing (NGS) followed by Polymerase Chain Reaction (PCR) and Sanger Sequencing.
Specimen Type
VariesSpecimen Minimum Volume
1 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Varies | Varies | ||
Reject Due To
All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.Reference Values
An interpretive report will be provided.
Interpretation
All detected variants are evaluated according to American College of Medical Genetics and Genomics recommendations.(5) Variants are classified based on known, predicted, or possible pathogenicity and reported with interpretive comments detailing their potential or known significance.
Method Description
Next-generation sequencing (NGS) and/or Sanger sequencing are performed to test for the presence of variants in coding regions and intron/exon boundaries of the CYB5A and CYB5R3 genes, as well as some other regions that have known disease-causing variants. The human genome reference GRCh37/hg19 build was used for sequence read alignment. At least 99% of the bases are covered at a read depth over 30X. Sensitivity is estimated at above 99% for single nucleotide variants, above 94% for deletions-insertions (delins) less than 40 base pairs (bp), above 95% for deletions up to 75 bp and insertions up to 47 bp. NGS and/or a polymerase chain reaction based quantitative method is performed to test for the presence of deletions and duplications in the CYB5A and CYB5R3 genes.
There may be regions of the genes that cannot be effectively evaluated by sequencing or deletion and duplication analysis as a result of technical limitations of the assay, including regions of homology, high guanine-cytosine (GC) content, and repetitive sequences.(Unpublished Mayo method)
The reference transcript for CYB5A is NM_001914.4 and the reference transcript for CYB5R3 is NM_000398.7. Reference transcript numbers may be updated due to transcript re-versioning. Always refer to the final patient report for gene transcript information referenced at the time of testing. Confirmation of select reportable variants may be performed by alternate methodologies based on internal laboratory criteria.
Day(s) Performed
Varies
Report Available
28 to 42 daysSpecimen Retention Time
Whole blood: 2 weeks (if available); Extracted DNA: 3 monthsPerforming Laboratory
Mayo Clinic Laboratories in Rochester
CPT Code Information
81479
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| NCYB | CYB5 and CYB5 Reductase, NGS | 103737-3 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 618978 | Test Description | 62364-5 |
| 618979 | Specimen | 31208-2 |
| 618980 | Source | 31208-2 |
| 618981 | Result Summary | 50397-9 |
| 618982 | Result | 82939-0 |
| 618983 | Interpretation | 59465-5 |
| 618984 | Additional Results | 82939-0 |
| 618985 | Resources | 99622-3 |
| 618986 | Additional Information | 48767-8 |
| 618987 | Method | 85069-3 |
| 618988 | Genes Analyzed | 82939-0 |
| 618989 | Disclaimer | 62364-5 |
| 618990 | Released By | 18771-6 |