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Test ID: GALK Galactokinase, Blood

Reporting Name

Galactokinase, B

Useful For

Diagnosis of galactokinase deficiency

 

Evaluation of children with unexplained bilateral congenital or juvenile onset cataracts

Testing Algorithm

See Galactosemia Testing Algorithm in Special Instructions for additional information.

Specimen Type

Whole Blood EDTA


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, 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.



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. 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


Specimen Minimum Volume

2 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Whole Blood EDTA Refrigerated (preferred) 10 days
  Ambient  72 hours

Reference Values

≥0.7 nmol/h/mg of hemoglobin

Day(s) Performed

Monday

Test Classification

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.

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

Clinical 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.

Interpretation

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.

Clinical Reference

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&sectionid=%20225081023

Report Available

8 to 15 days

Method Name

Enzyme Reaction followed by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Forms

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.

Mayo Clinic Laboratories | Genetics and Pharmacogenomics Catalog Additional Information:

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