Galactosemia: GALT (Full Gene Sequencing)

CPT: 81406
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Test Details

Test Includes

This test covers all coding nucleotides of gene GALT, plus at least two and typically 20 flanking intronic nucleotides upstream and downstream of each coding exon, covering the conserved donor and acceptor splice sites, as well as typically 20 flanking nucleotides in the 5′ and 3′ UTR.

Use

Confirm a clinical diagnosis of galactosemia; detect carriers; help to establish a prognosis

Limitations

This method does not reliably detect mosaic variants; large deletions; large duplications, inversions, or other rearrangements; or deep intronic variants. It may be affected by allele-dropout; it may not allow determination of the exact numbers of T/A or microsatellite repeats; and it does not allow any conclusion as to whether two heterozygous variants are present on the same or on different chromosome copies.

Results of this test are for investigational purposes only. The performance characteristics of this assay have been determined by LabCorp. The result should not be used as a diagnostic procedure without confirmation of the diagnosis by another medically established diagnostic product or procedure.

Methodology

DNA sequencing

Reference Interval

Normal equals reference sequence or variants that are known or predicted to be benign; abnormal equals all other variants.

Additional Information

Galactosemia is an autosomal recessive disorder of galactose metabolism that, if left untreated, can result in neonatal death. If the patient survives the neonatal period, mental retardation will develop. Most cases of galactosemia, which has a prevalence of about 1 in 30,000, are detected through newborn screening of galactose-1-phosphate uridyltransferase (GALT) enzyme activity and/or galactose-1 phosphate concentration in red blood cells. If GALT deficiency is detected, prompt removal of lactose and galactose from the diet can resolve acute neonatal symptoms and prevent death and mental retardation. Genetic testing of the gene encoding GALT can be used to confirm a newborn screening result and detect the specific mutations leading to galactosemia in a patient, with possible implications for disease prognosis.

Even with timely treatment initiation, long-term consequences are common and can include speech defect (verbal dyspraxia), delay of mental development, motor dysfunction, poor growth, cataracts, and, in females, ovarian failure. Prognosis may differ depending on the nature of the specific GALT mutation underlying the disease. Well known examples for this are the common Duarte and Los Angeles alleles, which cannot be distinguished by techniques such as isoelectric focusing. In contrast, genetic testing can differentiate between these two variants and also detect the hundreds of “private” variants that have been reported in GALT. Once the mutations causing galactosemia in a specific family have been identified, genetic testing for these mutations can also help to diagnose affected siblings of patients prenatally or directly after birth and facilitate genetic counseling in other relatives.

Specimen Requirements

Specimen

Whole blood; DNA is accepted (Call 800-435-4363 for DNA collection information.)

Volume

2 mL

Container

Lavender-top (EDTA) tube

Collection

Samples may be stored for brief periods at 4°C. Ship overnight at room temperature.

Storage Instructions

Maintain specimen at room temperature.

Causes for Rejection

Container broken or leaking; container not labeled or label not legible; use of improper anticoagulant

Clinical Information

Special Instructions

In cases in which a known mutation can be documented, the physician may prefer to order test 252820.

Test orders must include an attestation that the provider has the patient's informed consent for genetic testing. See sample physician office consent form: Consent for Genetic Testing. In the case of family tests (ie, known mutations), please submit the result report of the first patient tested in the family (the index case), if not performed at a LabCorp facility. Other family members are subsequently tested for the specific mutation found in the first patient tested.

References

Bosch AM. Classical galactosemia revisited. J Inherit Metab Dis. 2006; 29(4):516-525. 16838075
Elsas LJ II. Galactosemia. GeneReviews. 2007; Available at:http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=galactosemia. Accessed August 1, 2010. 20301691
Tyfield L, Reichardt J, Fridovich-Keil J, et al. Classical galactosemia and mutations at the galactose-1-phosphate uridyl transferase (GALT) gene. 1999; 13(6):417-430. 10408771

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
252816 Galactosemia: GALT 42318-6 252206 Routing 42318-6

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