Sorted By Test Name - Mayo Medical Laboratories

GCT
84360
classic galactosemia (G/G genotype). The most frequently observed is the Q188R mutation. This mutation
accounts for 60% to 70% of classic galactosemia alleles. The S135L mutation is the most frequently
observed mutation in African Americans and accounts for approximately 50% of the mutant alleles in this
population. The K285N mutation is common in those of eastern European descent and accounts for 25%
to 40% of the alleles in this population. The L195P mutation is observed in 5% to 7% of classic
galactosemia. The Duarte variant (N314D) is found in 5% of the general United States population. The
above mutations, plus the LA variant, are included in GCT/84360 Galactosemia Reflex, Blood, which is
the preferred test for the diagnosis of galactosemia or for follow-up to positive newborn screening results.
These mutations are also included in GAL6/84366 Galactosemia Gene Analysis (6-Mutation Panel). Full
sequencing of the GALT gene can be useful for the identification of mutations when 1 or no mutations are
found with these tests in an individual with demonstrated GALT enzyme deficiency. Full sequencing of
the GALT gene identifies over 95% of the sequence variants in the coding region and splice junctions.
Useful For: Diagnostic confirmation of galactosemia when familial mutations have been previously
identified Carrier screening of at-risk individuals when a mutation in the galactose-1-phosphate
uridyltransferase (GALT) gene has been identified in an affected family member
Interpretation: All detected alterations will be evaluated according to the American College of
Medical Genetics and Genomics (AMCG) recommendations. Variants will be classified based on known,
predicted, or possible pathogenicity and reported with interpretive comments detailing their potential or
known significance. Results should be interpreted in the context of biochemical results.
Reference Values:
An interpretive report will be provided.
Clinical References: 1. Elsas LJ 2nd, Lai K: The molecular biology of galactosemia. Genet Med
1998 Nov-Dec;1(1):40-48 2. Novelli G, Reichardt JK: Molecular basis of disorders of human galactose
metabolism: past, present, and future. Mol Genet Metab 2000 Sept-Oct;71(1-2):62-65 3. Bosch AM, Ijlst
L, Oostheim W, et al: Identification of novel mutations in classical galactosemia. Hum Mutat 2005
May:25(5):502 4. Richards CS, Bale S, Bellissimo DB, et al: ACMG recommendations for standards for
interpretation and reporting of sequence variations: Revisions 2007. Genet Med 2008;10(4):294-300
Galactosemia Reflex, Blood
Clinical Information: Classic galactosemia is an autosomal recessive disorder of galactose
metabolism caused by mutations in the galactose-1-phosphate uridyltransferase gene (GALT). The
complete or near-complete deficiency of the galactose-1-phosphate uridyltransferase (GALT) enzyme is
life threatening. If left untreated, complications include liver failure, sepsis, mental retardation, and death.
Galactosemia is treated by a galactose-free diet, which allows for rapid recovery from acute symptoms
and a generally good prognosis. Despite adequate treatment from an early age, children 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. The prevalence of classic
galactosemia is approximately 1/30,000. Duarte variant galactosemia (compound heterozygosity for the
Duarte mutation, N314D, and a classic mutation) is generally associated with higher levels of enzyme
activity (5%-20%) than classic galactosemia (