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.
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.
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.
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.
Isolation using the Perkin Elmer™Chemagen™ Chemagen™ Automated Extraction method or Qiagen™ Puregene kit for DNA extraction is recommended.
Infants and Young Children (<2 years of age): 2-3 ml
Children > 2 years of age to 10 years old: 3-5 ml
Older Children & Adults: 5-10 ml
Autopsy: 2-3 ml unclotted cord or cardiac blood
Orangene™ Saliva Collection Kit used according to manufacturer instructions. Please contact EGL for a Saliva Collection Kit for patients that cannot provide a blood sample.
- 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.