Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Galactokinase (GALK) deficiency is the second most common form of galactosemia, affecting approximately 1/250,000 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 lactose-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 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 mutations in the GALK1 gene. Gene analysis is available from some commercial laboratories. Contact Mayo Medical Laboratories for recommendations or contact information for laboratories that offer this testing.
See Galactosemia Testing Algorithm in Special Instructions.
Diagnosis of galactokinase deficiency, the second most common cause of galactosemia
An interpretive report will be provided.
See Galactosemia Testing Algorithm in Special Instructions for additional information.
For galactose-1-phosphate uridyltransferase deficiency, see GALT / Galactose-1-Phosphate Uridyltransferase, Blood.
For epimerase deficiency, see GALE / UDP-galactose 4’ epimerase (GALE), Blood.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
This assay is not useful for monitoring dietary compliance; see GAL1P / Galactose-1-Phosphate (Gal-1-P), Erythrocytes.
This assay will not detect epimerase (GALE) deficiency or galactose-1-phosphate uridyltransferase (GALT) deficiency.
It is important to notify the laboratory if the patient has been transfused prior to specimen collection. The results of testing performed in erythrocytes are invalid following a transfusion, including analysis of enzymes, biochemical phenotyping, or galactose-1-phosphate.
The most common cause of galactosemia is GALT deficiency (see GALT / Galactose-1-Phosphate Uridyltransferase [GALT], Blood). In most cases, GALT deficiency should be ruled out prior to evaluating for GALK deficiency.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
> or =0.7 nmol/h/mg of hemoglobin
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Li, Y, Ptolemy AS, Harmonay L, et al: Ultra fast and sensitive liquid chromatography tandem mass spectrometry based assay for galactose-1-phosphate uridylyltransferase and galactokinase deficiencies. Mol Gen Metab 2011;102(1):33-40
2. Ko DH, Jun SH, Park HD, et al: Multiplex enzyme assay for galactosemia using ultraperformance liquid chromatography-tandem mass spectrometry. Clin Chem 2010;56:764-771
3. Hennermann JB, Schadewaldt P, Vetter B, et al: Features and outcome of galactokinase deficiency in children diagnosed by newborn screening. J Inherit Metab Dis 2011;34:399-407
4. Walter JH, Fridovich-Keil JL: Galactosemia. In The Online Metabolic and Molecular Bases of Inherited Disease. Edited by D Valle, AL Beaudet, B Vogelstein, et al. McGraw-Hill, New York, 2014, Accessed January 26, 2016. Available at: http://ommbid.mhmedical.com/content.aspx?bookid=971&Sectionid=62672411