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Test ID: GALTP Galactose-1-Phosphate Uridyltransferase Biochemical Phenotyping, Erythrocytes

Reporting Name

Gal-1-Phos Urdyltrns Phenotype,RBC

Useful For

Determining the biochemical phenotype for galactosemia when enzymatic and molecular results are incongruent

Clinical Information

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.

 

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.

 

In general, molecular genetic analysis with a panel of common variants (GAL14/ Galactosemia Gene Analysis (14-Mutation Panel)) is typically performed to determine the specific genotype. If the enzymatic and molecular results are incongruent, biochemical phenotyping and/or molecular sequence analysis may be beneficial to help clarify results to determine a treatment strategy and recurrence risks.

 

See Galactosemia Testing Algorithm in Special Instructions for additional information.

Interpretation

An interpretive report will be provided.

 

See Galactosemia Testing Algorithm in Special Instructions for additional information.

Testing Algorithm

A quantitative galactose-1-phosphate uridyltransferase GALT) level is used in addition to the isoelectric focusing for accurate interpretation. If recent GALT test results are not provided, GALT will be automatically performed at an additional charge. However, if previous GALT results are provided, GALT testing will be cancelled and not charged.

 

See Galactosemia Testing Algorithm in Special Instructions.

Analytic Time

8 days

Day(s) and Time(s) Performed

Thursday; 9 a.m.

Clinical Reference

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

Method Name

GALTP: Isoelectric Focusing
GALT: Enzyme Reaction followed by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Specimen Type

Whole Blood EDTA


Advisory Information


GCT / Galactosemia Reflex, Blood is the preferred test to evaluate for possible diagnosis of galactosemia, routine carrier screening, and follow-up of abnormal newborn screening results.

 

For monitoring of dietary compliance, order GAL1P / Galactose-1-Phosphate (Gal-1-P), Erythrocytes.



Necessary Information


Patient's age is required.

 

A quantitative galactose-1-phosphate uridyltransferase level (GALT / Galactose-1-Phosphate Uridyltransferase, Blood) is required for accurate interpretation.

 

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: Lavender top (EDTA)

Specimen Volume: 3 mL


Specimen Minimum Volume

2 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Whole Blood EDTA Refrigerated (preferred) 28 days
  Ambient  14 days

Reference Values

An interpretative report will be provided.

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 U.S. Food and Drug Administration.

CPT Code Information

82664

82775

LOINC Code Information

Test ID Test Order Name Order LOINC Value
GALTP Gal-1-Phos Urdyltrns Phenotype,RBC In Process

 

Result ID Test Result Name Result LOINC Value
80341 Gal-1-Phos Urdyltrns Phenotype,RBC 33780-8
34524 Reviewed By 18771-6

Additional Tests

Test ID Reporting Name Available Separately Always Performed
GALT Gal-1-P Uridyltransferase, RBC Yes Yes

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 an Inborn Errors of Metabolism Test Request (T798) with the specimen.

Mayo Clinic Laboratories | Endocrinology Catalog Additional Information:

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