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Test ID: GALK    
Galactokinase, Blood

Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosis of galactokinase deficiency, the second most common cause of galactosemia

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 48 hours of draw.

 

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.

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.

<2 years: 20.1-79.8 mU/g of hemoglobin

> or =2 years: 12.1-39.7 mU/g of hemoglobin

Interpretation Provides information to assist in interpretation of the test results

Low values suggest galactokinase deficiency.

 

Only results below the normal range are clinically significant. Elevated values have no clinical significance.  

 

See Galactosemia Testing Algorithm in Special Instructions.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

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.

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

1. 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

2. Holton JB, Walter JH, Tyfield LA: Galactosemia. In The Metabolic and Molecular Basis of Inherited Disease. Eighth edition. Edited by CR Scriver, AL Beaudet, WS Sly, et al. New York, McGraw-Hill Book Company, 2001, pp 1553-1587

Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test