TEST CATALOG ORDERING & RESULTS SPECIMEN HANDLING CUSTOMER SERVICE EDUCATION & INSIGHTS
Test Catalog

Test ID: GALT    
Galactose-1-Phosphate Uridyltransferase, Blood

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

Diagnosis of galactose-1-phosphate uridyltransferase deficiency, the most common cause of galactosemia

 

Confirmation of abnormal state newborn screening results

Genetics Test Information Provides information that may help with selection of the correct genetic test or proper submission of the test request

Galactose-1-phosphate uridyltransferase (GALT) deficiency is the most common cause of galactosemia and requires lifelong restriction of dietary galactose.

 

Classic galactosemia can be diagnosed by analysis of GALT enzyme.

 

This test provides enzymatic testing for the diagnosis of galactose-1-phosphate uridyltransferase (GALT) deficiency.

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

See Galactosemia Testing Algorithm in Special Instructions.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Galactosemia is an autosomal recessive disorder that results from a deficiency of any 1 of the 3 enzymes catalyzing the conversion of galactose to glucose: galactose-1-phosphate uridyltransferase (GALT), galactokinase (GALK), and uridine diphosphate galactose-4-epimerase (GALE). GALT deficiency is the most common cause of galactosemia and is often referred to as classic galactosemia. The complete or near-complete deficiency of GALT enzyme is life threatening if left untreated. Complications in the neonatal period include failure to thrive, liver failure, sepsis, and death.

 

Galactosemia is treated by a galactose-restricted diet, which allows for rapid recovery from the acute symptoms and a generally good prognosis. Despite adequate treatment from an early age, individuals with galactosemia remain at increased risk for developmental delays, speech problems, and abnormalities of motor function. Females with galactosemia are at increased risk for premature ovarian failure. Based upon reports by newborn screening programs, the frequency of classic galactosemia in the United States is approximately 1 in 30,000, although literature reports range from 1 in 10,000 to 1 in 60,000 live births.

 

Galactose-1-phosphate (Gal-1-P) accumulates in the erythrocytes of patients with galactosemia. The quantitative measurement of Gal-1-P (GAL1P / Galactose-1-Phosphate [Gal-1-P], Erythrocytes) is useful for monitoring compliance with dietary therapy. Gal-1-P is thought to be the causative factor for development of liver disease in these patients and, because of this, patients should maintain low levels and be monitored on a regular basis.

 

Duarte-variant galactosemia (compound heterozygosity for the Duarte variant, N314D and a classic variant) is generally associated with higher levels of enzyme activity (5%-20%) than classic galactosemia (<5%); however, this may be indistinguishable by newborn screening assays. Previously, it was unknown whether children with Duarte-variant galactosemia were at an increased risk for adverse developmental outcomes due to milk exposure and were often treated with a low galactose diet during infancy. More recently, the outcomes data suggest a lack of evidence for developmental complications due to milk exposure, therefore treatment recommendations remain controversial. The Los Angeles variant, which consists of N314D and a second variant, L218L, is associated with higher levels of GALT enzyme activity than the Duarte-variant allele.

 

Newborn screening for galactosemia is performed in all 50 US states, though the method by which potentially affected individuals are detected varies from state to state and may include the measurement of total galactose (galactose and Gal-1-P) and/or determining the activity of the GALT enzyme. The diagnosis of galactosemia is established by follow-up quantitative measurement of GALT enzyme activity. If enzyme levels are indicative of carrier or affected status, molecular testing for common GALT variants may be performed. If 1 or both disease-causing variants are not detected by targeted variant analysis and biochemical testing has confirmed the diagnosis of galactosemia, sequencing of the GALT gene is available to identify private variations.

 

See Galactosemia Testing Algorithm in Special Instructions for additional information.

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 =24.5 nmol/h/mg of hemoglobin

Interpretation Provides information to assist in interpretation of the test results

An interpretive report will be provided.

 

See Galactosemia Testing Algorithm in Special Instructions for additional information.

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

The results of testing performed in erythrocytes, including analysis of enzymes, biochemical phenotyping, or galactose-1-phosphate are invalid following a transfusion.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Berry GT: Classic Galactosemia and Clinical Variant Galactosemia. In GeneReviews. Edited by MP Adam, HH Ardinger, RA Pagon, et al. University of Washington, Seattle Updated 2017 Mar 9 Accessed: February 20, 2020 Available at https://www.ncbi.nlm.nih.gov/books/NBK1518/

2. 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. Accessed June 18, 2019. Available at http://ommbid.mhmedical.com/content.aspx?bookid=971&sectionid=62672411

3. Carlock G, Fischer ST, Lynch ME, et al. Developmental Outcomes in Duarte Galactosemia. Pediatrics. 2018;143(1):e20182516. doi:10.1542/peds.2018-2516

Special Instructions Library of PDFs including pertinent information and forms related to the test