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Test Catalog

Test ID: BGA    
Beta-Galactosidase, Leukocytes

Useful For Suggests clinical disorders or settings where the test may be helpful

Aiding in the diagnosis of GM1 gangliosidosis, Morquio B disease, and galactosialidosis

 

This test is not suitable for carrier detection.

Genetics Test Information Provides information that may help with selection of the correct genetic test or proper submission of the test request

Beta-galactosidase enzyme is deficient in the following conditions: GM1 gangliosidosis, Morquio syndrome B, and galactosialidosis.

 

Careful review of clinical findings will help distinguish between GM1 gangliosidosis and Morquio syndrome type B.

 

A diagnosis of galactosialidosis must be additionally demonstrated by a deficiency of neuraminidase.

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Beta-galactosidase is a lysosomal enzyme responsible for catalyzing the hydrolysis of gangliosides. Isolated deficiency of this enzyme is expressed clinically as 2 different diseases, GM1 gangliosidosis and Morquio syndrome B. Galactosialidosis is also associated with a deficiency of beta-galactosidase but in conjunction with neuraminidase secondary to a defect in protective protein cathepsin A (CTSA). Enzymatic testing is not reliable for carrier detection of these conditions.

 

GM1 gangliosidosis is an autosomal recessive lysosomal storage disorder caused by reduced or absent beta-galactosidase activity. Absent or reduced activity leads to the accumulation of GM1 gangliosides, oligosaccharides, and keratan sulfate. The disorder can be classified into 3 subtypes that vary with regard to age of onset and clinical presentation. Type 1, or infantile onset, typically presents between birth and 6 months with a very rapid progression of hypotonia, dysostosis multiplex, hepatosplenomegaly, central nervous system degeneration, and death usually by 1 to 2 years. Type 2 is generally classified as late infantile or juvenile with onset between 7 months and 3 years and presenting with developmental delays or regression and a slower clinical course. Type 3 is an adult or chronic variant with onset between 3 and 30 years and is typically characterized by slowly progressive dementia with Parkinsonian features and dystonia. The incidence has been estimated to be 1 in 100,000 to 200,000 live births.

 

In mucopolysaccharidosis type IVB (MPS IVB, Morquio B), reduced or absent beta-galactosidase activity leads to the accumulation of glycosaminoglycans (GAG) in lysosomes and interferes with normal functioning of cells, tissues, and organs. MPS IVB typically manifests as a systemic skeletal disorder with variable severity ranging from early severe disease to a later onset attenuated form. Virtually all patients have dysostosis multiplex and short stature along with other symptoms that may include coarse facies, hepatosplenomegaly, hoarse voice, stiff joints, cardiac disease, but no neurological involvement.

 

Galactosialidosis is an autosomal recessive lysosomal storage disease (LSD) caused by variants in the cathepsin A gene (CTSA) resulting in a combined deficiency of the enzymes beta-galactosidase and neuraminidase. The disorder can be classified into 3 subtypes that vary with respect to age of onset and clinical presentation. Typical clinical presentation includes coarse facial features, cherry-red spots, and skeletal dysplasia. The early infantile form is associated with fetal hydrops, visceromegaly, skeletal dysplasia, and early death. The late infantile form typically presents with short stature, dysostosis multiplex, coarse facial features, hepatosplenomegaly, and/or heart valve problems. The majority of individuals with the juvenile/adult form of GS are of Japanese ancestry and develop symptoms after 4 years of age which include neurologic degeneration, ataxia, and angiokeratomas.

 

Patients with mucolipidosis II/III (I-cell disease) may also demonstrate deficiency of beta-galactosidase in leukocytes, in addition to deficiency of other hydrolases. I-cell disease is an autosomal recessive lysosomal storage disorder resulting in impaired transport and phosphorylation of newly synthesized lysosomal proteins to the lysosome due to deficiency of N-acetylglucosamine 1-phosphotransferase (GlcNAc). Characteristic clinical features include short stature, skeletal and cardiac abnormalities, and developmental delay. Measurement of beta-galactosidase activity is not the preferred diagnostic test for I-cell disease, but may be included in the testing strategy.

 

A diagnostic workup in an individual with GM1 gangliosidosis, Morquio B, or galactosialidosis typically demonstrates decreased beta-galactosidase enzyme activity in leukocytes or fibroblasts; however, additional testing and consideration of the patient's clinical findings are necessary to differentiate between these conditions. Follow-up testing may include LYSDU / Lysosomal Storage Disorders Screen, Random, Urine, which analyzes mucopolysaccharides, oligosaccharides, ceramide trihexosides, and sulfatides to  help differentiate between the 3 conditions and guide physicians in choosing the best confirmatory molecular testing option.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

> or =1.56 nmol/min/mg

Interpretation Provides information to assist in interpretation of the test results

Very-low enzyme activity levels are consistent with GM1 gangliosidosis and Morquio B disease. Clinical findings must be used to differentiate between those 2 diseases. The deficiency of beta-galactosidase combined with neuraminidase deficiency is characteristic of galactosialidosis.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

This test does not differentiate between GM1 gangliosiosis, Morquio B, and galactosialidosis.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Suzuki Y, Nanba E, Matsuda J, et al: Beta-Galactosidase Deficiency (Beta-Galactosidosis): GM1 Gangliosidosis and Morquio B Disease. In The Online Metabolic and Molecular Bases of Inherited Disease. Edited by D Valle, AL Beaudet, B Vogelstein, et al. New York, McGraw-Hill, Accessed March 11, 2019, Available athttps://ommbid.mhmedical.com/content.aspx?sectionid=225547263&bookid=2709&Resultclick=2

2. d'Azzo A, Andria G, Bonten E, Annunziata I: Galactosialidosis. In The Online Metabolic and Molecular Bases of Inherited Disease. Edited by D Valle, AL Beaudet, B Vogelstein, et al.  New York, McGraw-Hill, 2014, Accessed March 11, 2019, Available athttps://ommbid.mhmedical.com/content.aspx?sectionid=225547663&bookid=2709&Resultclick=2

3. Brunetti-Pierri N, Scaglia F: GM1 gangliosidosis: review of clinical, molecular, and therapeutic aspects. Mol Genet Metab 2008 Aug;94(4):391-396

4. Caciotti A, Garman SC, Rivera-Colon Y, et al: GM1 gangliosidosis and Morquio B disease: an update on genetic alterations and clinical findings. Biochim Biophys Acta 2011 Jul;1812(7):782-790

Special Instructions Library of PDFs including pertinent information and forms related to the test