Diagnosis of galactokinase deficiency
Evaluation of children with unexplained bilateral congenital or juvenile onset cataracts
Enzymatic testing for the diagnosis of galactokinase (GALK) deficiency.
See Galactosemia Testing Algorithm in Special Instructions for additional information.
Enzyme Reaction followed by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)
Galactokinase (RBC)
Galactokinase Deficiency
Galactosemia
See Galactosemia Testing Algorithm in Special Instructions for additional information.
Whole Blood EDTA
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, or uridine diphosphate-galactose 4' epimerase (GALE) 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
This assay is not appropriate for monitoring dietary compliance. If dietary monitoring is needed, order GAL1P / Galactose-1-Phosphate, Erythrocytes.
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.
Multiple whole blood tests for galactosemia can be performed on 1 specimen. Prioritize order of testing when submitting specimens. See Galactosemia-Related Test List in Special Instructions for a list of tests that can be ordered together.
Container/Tube:
Preferred: Lavender top (EDTA)
Acceptable: Green top (sodium or lithium heparin) or yellow top (ACD)
Specimen Volume: 4 mL
1. 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 in Special Instructions:
-Informed Consent for Genetic Testing (T576)
-Informed Consent for Genetic Testing-Spanish (T826)
2. Biochemical Genetics Patient Information (T602) is recommended, see Special Instructions.
3. If not ordering electronically, complete, print, and send a Biochemical Genetics Test Request (T798) with the specimen.
2 mL
Gross hemolysis | Reject |
Specimen Type | Temperature | Time | Special Container |
---|---|---|---|
Whole Blood EDTA | Refrigerated (preferred) | 10 days | |
Ambient | 72 hours |
Diagnosis of galactokinase deficiency
Evaluation of children with unexplained bilateral congenital or juvenile onset cataracts
Enzymatic testing for the diagnosis of galactokinase (GALK) deficiency.
See Galactosemia Testing Algorithm in Special Instructions for additional information.
Galactokinase (GALK) deficiency, is a very rare autosomal recessive disorder in the first step of galactose metabolism. Prevalence is unknown but 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 (GALT) 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. Gene analysis is available from some commercial laboratories. Call 800-533-1710 for recommendations or contact information for laboratories that offer this testing.
See Galactosemia Testing Algorithm in Special Instructions.
> or =0.7 nmol/h/mg of hemoglobin
An interpretive report will be provided.
Deficient galactokinase (GALK) enzyme activity in erythrocytes is diagnostic for galactokinase deficiency.
See Galactosemia Testing Algorithm in Special Instructions for additional information.
1. Li Y, Ptolemy AS, Harmonay L, Kellogg M, Berry GT: Ultra fast and sensitive liquid chromatography tandem mass spectrometry based assay for galactose-1-phosphate uridylyltransferase and galactokinase deficiencies. Mol Genet Metab. 2011 Jan;102(1):33-40. doi: 10.1016/j.ymgme.2010.08.018
2. 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 Jan;20(1):3-11. doi: 10.1038/gim.2017.172
3. 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 Apr;34(2):399-407. doi: 10.1007/s10545-010-9270-8.
4. Ramani PK, Arya K: Galactokinase deficiency. In: StatPearls [Internet]. StatPearls Publishing; 2021. Updated January 11, 2021. Accessed May 3, 2021. Available at www.ncbi.nlm.nih.gov/books/NBK560683/
5. 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 May 3, 2021. Available at https://ommbid.mhmedical.com/content.aspx?bookid=2709§ionid=%20225081023
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).
Monday
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.
82759
Test Id | Test Order Name | Order LOINC Value |
---|---|---|
GALK | Galactokinase, B | 81143-0 |
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.
|
---|---|---|
38005 | Galactokinase, B | 81143-0 |
38007 | Interpretation (GALK) | 59462-2 |
38006 | Reviewed By | 18771-6 |