Galactosemia: GALT Gene Sequencing

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Condition Description

Galactosemia is an autosomal recessive disorder of galactose metabolism that often presents in the newborn period with poor suck, vomiting, diarrhea, bleeding diathesis, lethargy, jaundice, and sepsis. If left untreated, an individual may progress to irreversible liver disease and mental retardation. The prevalence of galactosemia is approximately 1 in 30,000 newborns. Most often galactosemia is caused by a deficiency of the galactose-1-phosphate uridyltransferase (GALT) enzyme, which catalyzes the conversion of the galactose-1-phosphate to glucose-1-phosphate. This is a critical step in the metabolism of galactose to glucose.

The GALT gene is encoded by 11 exons on chromosome 9p13. Galactosemia caused by mutations in the GALT gene is inherited in an autosomal recessive manner.

Family members of individuals with galactosemia are at risk to be carriers of the disorder. Biochemical and molecular screening is available to family members or partners of individuals with galactosemia using a combination of mutation analysis and enzyme activity.

Visit www.ThinkGenetic.com for patient-friendly information on galactosemia.

Reference:

Genes (1)

Indications

This test is indicated for individuals with biochemical diagnosis of a galactosemia or carrier status and a negative or unknown result from mutation analysis for common GALT gene mutations.

This test is NOT recommended for galactosemia screening or diagnosis in persons with a positive newborn screen. Please refer to the Classic Galactosemia Panel.

Methodology

PCR is used to amplify the 11 coding exons, immediate flanking regions, and the 4bp promoter deletion region of the GALT gene. The 5.0kb deletion is tested for by allele specific PCR.

Detection

This assay will detect over 95% of the sequence variants in the coding region and splice junctions. Mutations in the promoter region, some mutations in the introns, and other regulatory elements cannot be detected by this analysis. Large deletion and insertion mutations will not be detected by this assay. It is possible that some patients with a typical presentation may not carry a mutation detected by this analysis. This analysis may detect novel variants of unclear effect, which may require further studies.

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 (Children (>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 EGL) 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 outside of Emory Genetics Laboratory, please submit a copy of the sequencing report with the test requisition. Contact the laboratory if further information is needed.

  • Comprehensive GALT Analysis it the standard galactosemia test offered by EGL includes GALT enzyme activity, isozyme pattern (phenotyping), and gal-1-p level.
  • Carrier Testing for Galactosemia is accomplished by looking at GALT and isozyme.
  • Custom Diagnostic Mutation Analysis is available to individuals if the familial mutation is not included in the common mutation panel. Please contact the laboratory genetic counselor to arrange testing.
  • A Deletion/Duplication Assay is available separately for individuals where mutations are not identified by sequence analysis. Refer to the test requisition or contact the laboratory for more information.
  • Prenatal testing may be available to couples who are confirmed carriers of galactosemia by molecular and biochemical analysis. Please contact the laboratory genetic counselor to determine the availability of prenatal testing.

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