Test Code: 2930

Galactosemia (Epimerase): GALE Gene Sequencing
Test Code: 2930
Turnaround time: 5 weeks

CONDITION DESCRIPTION

UDP-Galactose-4-Epimerase (GALE) deficiency is one of the three known forms of galactosemia, along with galactose-1-phosphate uridyltransferase (GALT) deficiency (classic galactosemia) and galactokinase (GALK) deficiency [1-2]. GALE deficiency has been defined as a continuous disorder with a spectrum of enzyme impairment and corresponding metabolic compromise impacting a variety of tissues in affected individuals [3]. The patients may present with symptoms reminiscent of classic galactosemia and demonstrate severely impaired GALE activity in both RBCs and lymphoblast resulting in accumulation of abnormally high levels of RBC galactose, gal-1P and UDP-gal.

GALE deficiency should be considered in individuals with elevated RBC galactose, gal-1-P and UDP-gal but normal GALT enzyme activity. Mutations in the GALE gene, located on 1p36, are associated with a biochemical diagnosis of GALE deficiency [3]. Gene sequence analysis is available to test for mutations in the GALE gene in patients with a biochemical diagnosis of GALE deficiency (test code: 2930). For patients with mutations not identified by full gene sequencing, a separate deletion/duplication assay is available using a targeted CGH array (test code: 8509).

References:
1. Fridovich-Keil JL. Galactosemia: the good, the bad, and the unknown. J Cell Physiol 2006, 209(3):701-5.
2. Holton et al. Galactosemia. In: Scriver CR, Beaudet AL, Sly WS, Valle D (eds) The Metabolic and Molecular Bases of Inherited Disease. McGraw- Hill, New York, pp. 1573-1575 (2001).
3. Openo et al. Epimerase-deficiency galactosemia is not a binary condition. Am J Hum Genet 2006, 78(1):89-102.

GENES
GALE

INDICATIONS
This test is indicated for:

  • Individuals with elevated gal-1-P and UDP-gal but with normal GALT and GALK enzyme activity and biochemical findings consistent with GALE deficiency
  • Carrier testing for individuals with a family history of GALE deficiency

METHODOLOGY

PCR amplification of 10 exons contained in the GALE gene is performed on patient genomic DNA. Direct sequencing of amplification products is performed in both the forward and reverse directions using automated fluorescence dideoxy sequencing methods. Patient gene sequences are compared to a normal reference sequence. Sequence variations are then classified as mutations, benign variants unrelated to disease or variations of unknown clinical significance. Variants of unknown clinical significance may require further studies of the patient and/or family members. This assay does not interrogate the promoter region, deep intronic regions or other regulatory elements. Large deletions are not detected by this analysis.

DETECTION
One study identified 23 distinct base changes in 8 patients, of which 20 were novel [3]. Results of molecular analysis must be interpreted in the context of the patient’s clinical and/or biochemical phenotype.

SPECIMEN REQUIREMENTS

Submit only 1 of the following specimen types
* Preferred specimen type: Whole Blood

Type: Whole Blood
Specimen Requirements:
In EDTA (purple top) or ACD (yellow top) tube: Infants (2 years): 3-5 ml
Older Children & Adults: 5-10 ml

Specimen Collection and Shipping: Refrigerate until time of shipment. Ship sample within 5 days of collection at room temperature with overnight delivery.

Type: Saliva
Specimen Requirements:
OrageneTM Saliva Collection kit (available through CEN4GEN) used according to manufacturer instructions.

Specimen Collection and Shipping: Store sample at room temperature. Ship sample within 5 days of collection at room temperature with overnight delivery.

SPECIAL INSTRUCTIONS
Submit copies of diagnostic biochemical test results with the sample. Sequence analysis is required before deletion/duplication analysis by targeted CGH array. If sequencing is performed by another third party provider, please submit a copy of the sequencing report with the test requisition.

RELATED TESTS
• Sequencing of GALT and GALK Genes for transferase deficient and galactokinase deficient galactosemia
• Custom Diagnostic Mutation Analysis (test code: 6875) is available to family members if mutations are identified by sequencing.
• For comprehensive testing a deletion/duplication assay is available separately. This test is indicated for individuals where mutations are not identified by sequence analysis. Refer to the test requisition for more information.