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CBGT
8297
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
patients with classic galactosemia. The Duarte mutation (N314D) is observed in 5% of the general United
States population. The above mutations, in addition to the LA variant, are included in GAL6/84366
Galactosemia Gene Analysis (6 Mutation Panel). See Galactosemia Reflex Algorithm in Special
Instructions for additional information. Refer to Galactosemia: Current Testing Strategy and Aids for Test
Selection, Mayo Medical Laboratories Communique 2005 May;30(5) for more information regarding
diagnostic strategy.
Useful For: Diagnosis, carrier detection, and determination of genotype of galactose-1-phosphate
uridyltransferase deficiency, the most common cause of galactosemia Differentiating Duarte variant
galactosemia from classic galactosemia Confirming results of newborn screening programs
Interpretation: The laboratory provides an interpretation of the results, including
galactose-1-phosphate uridyltransferase enzyme activity and genotype, if necessary. This interpretation
provides an overview of the results and their significance, a correlation to available clinical information,
elements of differential diagnosis, and recommendations for additional testing. Any specimen where
enzyme activity is or =18.5 U/g of hemoglobin
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 Sep-Oct;71(1-2):62-65 3. Walter JH,
Collins JE, Leonard JV: Recommendations for the management of galactosemia. Arch Dis Child 1999
Jan;80(1):93-96
Galactosylceramide Beta-Galactosidase, Fibroblasts
Clinical Information: Krabbe disease (globoid cell leukodystrophy) is an autosomal recessive
disorder caused by a deficiency of galactosylceramide beta-galactosidase (GBG). A deficiency of this
enzyme leads to an accumulation of galactosylceramide in globoid cells (multinucleated macrophages)
causing severe demyelination throughout the brain. The toxic metabolite galactosylsphingosine
(psychosine), an apoptotic compound, accumulates in oligodendrocytes and Schwann cells and
contributes to disease pathogenicity. Severely affected individuals typically present between 3 to 6
months of age with increasing irritability and sensitivity to stimuli. Rapid neurodegeneration follows with
death usually occurring by age 2. There are later onset forms of the disease that are characterized by
ataxia, vision loss, weakness, and psychomotor regression. The clinical course of Krabbe disease can be
variable even within the same family. Treatment is mostly supportive, although hematopoietic stem cell
transplantation has shown some success if treatment begins before neurologic damaged has occurred.
Krabbe disease is caused by mutations in the GALC gene located on 14q31. Over 60 mutations have been
described to date. Molecular genetic analysis, including deletion/duplication analysis, is commercially
available in the United States. Contact Mayo Medical Laboratories for recommendations or contact
information for laboratories that offer this testing.
Useful For: Diagnosis of Krabbe disease
Interpretation: Values below the reference range are consistent with a diagnosis of Krabbe disease.
The upper limit of normal may change with the specific activity of the substrate. Elevated values have no
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