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HelpMayo Test ID GALK Galactokinase, Blood
Ordering Guidance
This test is for diagnosis of galactokinase (GALK) deficiency and does not detect either galactose-1-phosphate uridyltransferase (GALT) deficiency (the most common cause of galactosemia), uridine diphosphate-galactose 4' epimerase (GALE) deficiency, or galactose mutarotase (GALM) deficiency. In most cases, GALT deficiency should be ruled out prior to evaluating for GALK deficiency.
-The preferred test to evaluate for possible diagnosis of galactosemia, routine carrier screening, and follow-up of abnormal newborn screening results is GCT / Galactosemia Reflex, Blood.
-To evaluate GALT deficiency only, order GALT / Galactose-1-Phosphate Uridyltransferase, Blood
-To evaluate for GALE deficiency only, order GALE / UDP-Galactose 4' Epimerase (GALE), Blood
-To evaluate for GALM deficiency, order GALP / Galactose, Plasma and molecular analysis of the GALM gene.
This assay is not appropriate for monitoring dietary compliance. If dietary monitoring is needed, order GAL1P / Galactose-1-Phosphate, Erythrocytes.
Necessary Information
Biochemical Genetics Patient Information (T602) is recommended, but not required, to be filled out and sent with the specimen to aid in the interpretation of test results.
Specimen Required
Multiple whole blood tests for galactosemia can be performed on 1 specimen. Prioritize order of testing when submitting specimens. For a list of tests that can be ordered together see Galactosemia-Related Test List.
Container/Tube:
Preferred: Lavender top (EDTA)
Acceptable: Green top (sodium or lithium heparin) or yellow top (ACD)
Specimen Volume: 4 mL
Useful For
Diagnosis of galactokinase deficiency
Evaluation of children with unexplained bilateral congenital or juvenile onset cataracts
Testing Algorithm
For more information see Galactosemia Testing Algorithm.
Special Instructions
Method Name
Enzyme Reaction followed by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
Reporting Name
Galactokinase, BSpecimen Type
Whole Blood EDTASpecimen Minimum Volume
2 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Whole Blood EDTA | Refrigerated (preferred) | 10 days | |
| Ambient | 72 hours |
Reject Due To
| Gross hemolysis | Reject |
Clinical Information
Galactokinase (GALK) deficiency is a very rare autosomal recessive disorder in the first step of galactose metabolism. Prevalence is unknown but is estimated to be approximately 1 in 50,000-1 in 100,000 live births, with a higher frequency in the Romani population. Individuals with GALK deficiency have a milder clinical presentation than that seen in patients with classic galactosemia, galactose-1-phosphate uridyltransferase deficiency. The major clinical manifestation is bilateral juvenile cataracts.
GALK deficiency is treated with a galactose-restricted diet. Early treatment may prevent or reverse the formation of cataracts.
In GALK deficiency, erythrocyte galactose-1-phosphate levels are generally normal, and plasma or urine galactose levels are generally elevated. The diagnosis is established by demonstrating deficient GALK enzyme activity in erythrocytes. Testing for GALK deficiency should be performed when there is a suspicion of galactosemia, either based upon the patient's clinical presentation or laboratory studies and GALT deficiency has been excluded. Specimens sent for GALT analysis may be used for GALK testing if the original specimen was received in the laboratory within the stability parameters listed in Specimen Stability Information.
GALK deficiency is caused by variants in the GALK1 gene. Molecular analysis of the GALK1 gene is available; order CGPH / Custom Gene Panel, Hereditary, Next-Generation Sequencing, Varies and specify Gene List ID: IEMCP-C2DU1U.
For more information see Galactosemia Testing Algorithm.
Reference Values
≥0.7 nmol/h/mg of hemoglobin
Interpretation
An interpretive report will be provided.
Deficient galactokinase enzyme activity in erythrocytes is diagnostic for galactokinase deficiency.
Cautions
The results of testing performed in erythrocytes, including analysis of enzymes, biochemical phenotyping, or galactose-1-phosphate, are invalid following a transfusion.
Clinical Reference
1. Pasquali M, Yu C, Coffee B. Laboratory diagnosis of galactosemia: a technical standard and guideline of the American College of Medical Genetics and Genomics (ACMG). Genet Med. 2018;20(1):3-11. doi:10.1038/gim.2017.172
2. Hennermann JB, Schadewaldt P, Vetter B, Shin YS, Monch E, Klein J. Features and outcome of galactokinase deficiency in children diagnosed by newborn screening. J Inherit Metab Dis. 2011;34(2):399-407. doi:10.1007/s10545-010-9270-8
3. Ramani PK, Arya K. Galactokinase deficiency. In: StatPearls [Internet]. StatPearls Publishing; 2021. Updated July 31, 2023. Accessed September 12, 2024. Available at www.ncbi.nlm.nih.gov/books/NBK560683/
4. Walter JH, Fridovich-Keil JL. Galactosemia. In: Valle D, Antonarakis S, Ballabio A, Beaudet AL, Mitchell GA, eds. The Online Metabolic and Molecular Bases of Inherited Disease. McGraw-Hill; 2019 Accessed September 12, 2024. Available at https://ommbid.mhmedical.com/content.aspx?bookid=2709§ionid=%20225081023
Method Description
A buffered enzyme incubation with substrate and cofactors is performed on lysed red blood cells. A post-incubation extraction is performed and subjected to liquid chromatography tandem mass spectrometry. The ratio of the extracted product to its internal standard is used to calculate the total enzymatic product. This is then normalized using the calculated hemoglobin concentration to determine the patient's enzyme level in nmol/h/mg of hemoglobin.(Unpublished Mayo method).
Day(s) Performed
Monday
Report Available
5 to 11 daysSpecimen Retention Time
2 monthsPerforming Laboratory
Mayo Clinic Laboratories in Rochester
Test Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
82759
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| GALK | Galactokinase, B | 81143-0 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 38005 | Galactokinase, B | 81143-0 |
| 38007 | Interpretation (GALK) | 59462-2 |
| 38006 | Reviewed By | 18771-6 |