Genetic confirmation of a dehydrated hereditary stomatocytosis-2/hereditary xerocytosis diagnosis with the identification of an alteration known or suspected to cause disease in the KCNN4 gene
Second-tier testing for patients in whom previous targeted gene variant analyses were negative for a specific red blood cell (RBC) membrane disorder
Establishing a diagnosis of a hereditary RBC membrane disorder, allowing for appropriate management and surveillance of disease features based on the gene involved, especially if splenectomy is a consideration
This test detects pathogenic alterations within the KCNN4 gene which are associated with hereditary stomatocytosis.
The gene target for this test includes the following:
Gene name (transcript): KCNN4 (GRCh37 (hg19) NM_002250)
Chromosomal location: chr19q13.31
Variants in KCNN4 are associated with a rare red blood cell membrane disorder, dehydrated hereditary stomatocytosis, which causes chronic hemolytic anemia.
Informative protein studies (eg, osmotic fragility, ektacytometry) and peripheral blood findings, correlated with the patient clinical history, should be performed prior to genetic testing.
Polymerase Chain Reaction (PCR) Amplification/Sanger Sequencing
DHS2
DHSt 2
Potassium calcium-activated channel subfamily N member 4
Varies
The following information is required on either the Metabolic Hematology Next-Generation Sequencing (NGS) Patient Information (T816) or test request form:
1. Clinical diagnosis
2. Pertinent clinical history (submit complete blood cell count results and relevant clinical notes)
3. Differentials based on clinical or morphologic presentation
4. Date of collection
5. Specimen type, whole blood or extracted DNA
Submit only 1 of the following specimens:
Preferred:
Specimen Type: Whole blood
Container/Tube:
Preferred: Lavender top (EDTA) or yellow top (ACD)
Acceptable: Green top (heparin)
Specimen Volume: 3 mL
Collection Instructions:
1. Invert several times to mix blood.
2. Send whole blood specimen in original tube. Do not aliquot.
3. Label specimen as blood.
Specimen Stability Information: Ambient 14 days (preferred)/Refrigerated < or =30 days
Acceptable:
Specimen Type: Extracted DNA from whole blood
Container/Tube: 1.5- to 2-mL tube with indication of volume and concentration of DNA
Specimen Volume: Entire specimen
Collection Instructions: Label specimen as extracted DNA from blood and provide indication of volume and concentration of the DNA
Specimen Stability Information: Frozen/Refrigerate/Ambient < or =30 days
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.
Blood: 1 mL
Extracted DNA: 50 mcL at 50 ng/mcL concentration
| Gross hemolysis | Reject |
| Gross lipemia | OK |
| Bone marrow biopsies Paraffin-embedded tissue Frozen tissue Slides Paraffin-embedded bone marrow aspirate clot Methanol-acetic acid fixed pellets Moderately to severely clotted | Reject |
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Varies | Varies | ||
Genetic confirmation of a dehydrated hereditary stomatocytosis-2/hereditary xerocytosis diagnosis with the identification of an alteration known or suspected to cause disease in the KCNN4 gene
Second-tier testing for patients in whom previous targeted gene variant analyses were negative for a specific red blood cell (RBC) membrane disorder
Establishing a diagnosis of a hereditary RBC membrane disorder, allowing for appropriate management and surveillance of disease features based on the gene involved, especially if splenectomy is a consideration
This test detects pathogenic alterations within the KCNN4 gene which are associated with hereditary stomatocytosis.
The gene target for this test includes the following:
Gene name (transcript): KCNN4 (GRCh37 (hg19) NM_002250)
Chromosomal location: chr19q13.31
Dehydrated hereditary stomatocytosis-2 (DHS2) (also called hereditary xerocytosis) is an autosomal dominant hereditary hemolytic disorder caused by an abnormal cation leak in the red blood cell membrane, resulting in loss of a potassium cation and red blood cell dehydration. Pseudohyperkalemia (loss of red blood cell potassium when cold or at room temperature) can be a feature. Symptoms include compensated to mild hemolytic anemia, moderate splenomegaly, elevated reticulocyte count, increased mean corpuscular volume (MCV), variably increased mean corpuscular hemoglobin concentration (MCHC), perinatal edema, and a tendency for iron overload. Red blood cells exhibit various shape abnormalities on blood smear, including elliptocytes, schizocytes, and rare stomatocytes.
The majority of symptomatic DHS cases reported to date have been associated with gain-of-function alterations in the mechanosensitive cation channel gene, PIEZO1. However, recent studies have identified families with DHS associated with variants in the KCNN4 gene.(1-4) KCNN4 encodes for the Gardos channel, the erythroid voltage-independent potassium channel that is activated by intracellular calcium.(4) Disease-causing alterations in KCNN4 result in decreased intracellular total cation and potassium levels. Cases reported have shown abnormal ektacytometry curves typical of hereditary xerocytosis. Clinical features of KCNN4 patients include hemolytic anemia of variable severity, which can be more severe in the perinatal period. Splenectomy may have no efficacy in symptom improvement in the few cases with KCNN4 variants.(2,5)
This test is best interpreted in the context of protein studies and peripheral blood findings. This can be provided by also ordering RBCME / Red Blood Cell Membrane Evaluation, Blood. Fill out the information sheet and indicate that KCNN4 testing was ordered. Providing complete blood cell count data and clinical notes will allow more precise interpretation of results.
An interpretive report will be provided.
Evaluation and categorization of variants is performed using the most recent published American College of Medical Genetics and Genomics recommendations as a guideline.(3) Variants are classified based on known, predicted, or possible pathogenicity and reported with interpretive comments detailing their potential or known significance.
Multiple in silico evaluation tools may be used to assist in the interpretation of these results. The accuracy of predictions made by in silico evaluation tools is highly dependent upon the data available for a given gene, and predictions made by these tools may change over time. Results from in silico evaluation tools should be interpreted with caution and professional clinical judgment.
Clinical:
Some individuals may have a sequence variant that is not identified by the methods performed. The absence of a variation, therefore, does not eliminate the possibility of hereditary hemolytic anemia or a related disorder. This assay does not distinguish between germline and somatic alterations, particularly with variant allele frequencies significantly lower than 50%. Test results should be interpreted in context of clinical findings, family history, and other laboratory data. Misinterpretation of results may occur if the information provided is inaccurate or incomplete.
If there is a family history of a hereditary hemolytic anemia or a related disorder, it is often useful to test first-degree family members to help establish the clinical significance of variants of unknown significance.
At this time, it is not standard practice for the laboratory to systematically review likely disease-causing variants or variants of uncertain significance that have been previously detected and reported. The laboratory encourages health care providers to contact the laboratory at any time to learn how the status of a particular variant may have changed over time.
Technical:
Some genetic or genomic alterations, such as large deletion-insertion (delin) events, copy number alterations, and gene translocation events are not detected by this assay. The depth of coverage may be variable for some target regions, but assay performance below the minimum acceptable criteria or for failed regions will be noted. Additionally, rare variants (ie, polymorphisms) may be present that could lead to false-negative or false-positive results. If results do not match clinical findings, consider alternative methods for analyzing these genes, such as Sanger sequencing or large deletion and duplication analysis. If the patient has had an allogenic blood transfusion, these results may be inaccurate due to the presence of donor DNA.
1. Glogowska E, Lezon-Geyda K, Maksimova Y, et al: Mutations in the Gardos channel (KCNN4) are associated with hereditary xerocytosis. Blood. 2015 Sep 10;126(11):1281-1284. doi: 10.1182/blood-2015-07-657957
2. Andolfo I, Russo R, Manna F, et al: Novel Gardos channel mutations linked to dehydrated hereditary stomatocytosis (xerocytosis). Am J Hematol. 2015 Oct;90(10):921-926. doi: 10.1002/ajh.24117
3. Richards S, Aziz N, Bale S, et al: Standards and guidelines for the interpretation of sequence variants: a joint consensus recommendation of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology. Genet Med. 2015 May;17(5):405-424. doi: 10.1038/gim.2015.30
4. Rapetti-Mauss R, Lacoste C, Picard V, et al: A mutation in the Gardos channel is associated with hereditary xerocytosis. Blood. 2015 Sep;126(11):1273-1280. doi: 10.1182/blood-2015-04-642496
5. Iolascon A, Andolfo I, Barcellini W, et al: Working Study Group on Red Cells and Iron of the EHA. Recommendations regarding splenectomy in hereditary hemolytic anemias. Haematologica. 2017 Aug;102(8):1304-1313. doi: 10.3324/haematol.2016.161166
6. Andolfo I, Russo R, Rosato BE, et al: Genotype-phenotype correlation and risk stratification in a cohort of 123 hereditary stomatocytosis patients. Am J Hematol. 2018 Dec;93(12):1509-1517. doi: 10.1002/ajh.25276
7. Gallagher PG: Disorders of erythrocyte hydration. Blood. 2017 Dec 21;130(25):2699-2708. doi: 10.1182/blood-2017-04-590810
8. Fermo E, Bogdanova A, Petkova-Kirova P, et al: 'Gardos Channelopathy': a variant of hereditary Stomatocytosis with complex molecular regulation. Sci Rep. 2017 May 11;7(1):1744. doi: 10.1038/s41598-017-01591-w
Total genomic DNA is extracted from the sample, and the full KCNN4 gene is amplified by polymerase chain reaction followed by Sanger sequencing of the 5' and 3'UTR (untranslated regions) and exons 1-9, including 10 base pairs on each intron/exon boundary. Review of the sequence data is performed using a combination of automated calls and manual inspection.(Unpublished Mayo method)
Monday through Friday
This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.
81479
| Test Id | Test Order Name | Order LOINC Value |
|---|---|---|
| KCNN4 | KCNN4 Full Gene Sequencing, V | 98954-1 |
| Result Id | Test Result Name |
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|
|---|---|---|
| 607810 | Interpretation | 82939-0 |
| 607811 | Signing Pathologist | 19139-5 |