Test ID: BGAT
Beta-Galactosidase, Fibroblasts

Diagnosis of GM1 gangliosidosis, Morquio syndrome B, and galactosialidosis

Not recommended for carrier detection.

When this test is ordered, a fibroblast culture and cryopreservation for biochemical studies will always be performed at an additional charge. However, for multiple lysosomal enzyme assays on a patient utilizing fibroblast culture, only 1 culture is required regardless of the number of enzyme assays ordered. If viable cells are not obtained within 10 days, client will be notified.

• Informed Consent for Genetic Testing

BGAT/8008: Fluorometric Enzyme Assay

FIBR/8482: Cultivated from Biopsy as Monolayer

CRYOB/88832: Fibroblast Subculture Followed by Cryopreservation and Storage

This test is not recommended for prenatal testing.

Forms:

1.   1. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (Supply T576) is available in Special Instructions.

2.   2. If not ordering electronically, submit a Biochemical Genetics Request Form (Supply T439) with the specimen.

Submit only 1 of the following specimens:

Specimen Type: Cultured fibroblasts

Container/Tube: T-75 or T-25 flask

Specimen Volume: 1 full T-75 flask or 2 full T-25 flasks

Specimen Stability Information: Ambient (preferred)/Refrigerated <24 hours

Specimen Type: Skin biopsy

Container/Tube: Sterile container with any standard cell culture media (eg, minimal essential media, RPMI 1640). The solution should be supplemented with 1% penicillin and streptomycin. Tubes can be supplied upon request (Eagle's minimum essential medium with 1% penicillin and streptomycin [Supply T115]).

Specimen Volume: 4-mm punch

Specimen Stability Information: Refrigerated (preferred)/Ambient

Beta-galactosidase is a lysosomal enzyme responsible for catalyzing the hydrolysis of gangliosides. The deficiency of this enzyme can lead to the following conditions: GM1 gangliosidosis, Morquio syndrome B, and galactosialidosis.

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 presenting with developmental delays and a slower progression. 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.

Mucopolysaccharidosis type IVB (MPS IVB, Morquio B) is an autosomal recessive lysosomal storage disorder caused by reduced or absent beta-galactosidase activity. The mucopolysaccharidoses are a group of disorders caused by the deficiency of any of the enzymes involved in the stepwise degradation of dermatan sulfate, heparan sulfate, keratan sulfate, or chondroitin sulfate (glycosaminoglycans; GAGs). Accumulation of GAGs (also known as mucopolysaccharides) in lysosomes interferes with normal functioning of cells, tissues, and organs. MPS IVB is caused by a reduced or absent activity of the beta-galactosidase enzyme and gives rise to the physical manifestations of the disease. Clinical features and severity of symptoms of MPS IVB are widely variable ranging from severe disease to an attenuated form, which generally presents at a later onset with a milder clinical presentation. In general, symptoms may include coarse facies, short stature, hepatosplenomegaly, hoarse voice, stiff joints, cardiac disease, but no neurological involvement. Treatment options are limited to symptomatic management.

Galactosialidosis is an autosomal recessive lysosomal storage disease associated with a combined deficiency of beta-galactosidase and neuraminidase secondary to a defect in the cathepsin A protein. The disorder can be classified into 3 subtypes that vary with regard to age of onset and clinical presentation. Typical clinical presentation is coarse facial features, cherry-red spots, or skeletal dysplasia. The early infantile form is associated with fetal hydrops, 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 juvenile/adult form is typically characterized by progressive neurologic degeneration, ataxia, and/or angiokeratomas. The incidence of the juvenile/adult form is greater in individuals with Japanese ancestry.

A diagnostic workup in an individual with GM1 gangliosidosis, Morquio B, or galactosialidosis typically demonstrates decreased beta-galactosidase enzyme activity in leukocytes and/or fibroblasts; however, enzymatic testing is not reliable to detect carriers. Individuals with galactosialidosis would also have decreased neuraminidase activity in leukocytes and/or fibroblasts in addition to decreased beta-galactosidase enzyme activity. Molecular sequence analysis of the GLB1 gene allows for detection of the disease-causing mutations in affected patients with GM1 gangliosidosis and/or Morquio B and sequencing of the CTSA gene allows for detection of disease-causing mutations in patients with galactosialidosis.

4.7-19.1 U/g of cellular protein

Values <4.7 U/g of cellular protein are consistent with a diagnosis of GM1 gangliosidosis, Morquio syndrome B, and, only if neuraminidase activity is also deficient, galactosialidosis.

This test is not suitable for carrier detection.

Leukocytes are the preferred specimen for the diagnosis of GM1 gangliosidosis.

Because beta-galactosidase is decreased in 3 clinically distinct disorders, a careful review of the clinical findings is necessary to differentiate between GM1 gangliosidosis and Morquio syndrome B. Patients with galactosialidosis will also exhibit decreased neuraminidase values in addition to decreased beta-galactosidase.

Interfering factors include lack of viable cells, bacterial contamination, failure to transport tissue in an appropriate media, excessive transport time, and exposure of the specimen to temperature extremes (freezing or >30 degrees C).

1. Suzuki Y, Sakuraba H, Oshima A: Beta-galactosidase deficiency (GM1 gangliosidosis, Morquio's syndrome type B) In The Metabolic Basis of Inherited Disease. Vol 2. Seventh edition. Edited by CR Scriver, AL Beaudet, WS Sly, et al. New York, McGraw-Hill Book Company, 1995, pp 2785-2838

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

The beta-galactosidase activity measured in this assay is 1 of the lysosomal enzymes which act at an acidic pH. It is present in liver, kidney, brain, fibroblasts, and leukocytes. Its natural substrate appears to be monosialoganglioside (GM1 ganglioside). The enzyme also hydrolyzes artificial substrates such as p-nitrophenyl beta-D-galactopyranoside and 4-methylumbelliferyl beta-D-galacto-pyranoside. The 4-methylumbelliferone produced is measured fluorometrically.(Modified from Ho MW, O'Brien JS: Differential effect of chloride ions on beta-galactosidase isoenzymes: a method for separate assay. Clin Chim Acta 1971;32:443-450; Gehler J, Cantz M, Tolksdorf M, Spranger J: Mucopolysaccharidosis. VII. Beta-glucuronidase deficiency. Humangenetik 1974;23:149-158)

Varies

82657-Beta-galactosidase

88233-Fibroblast culture

88240-Cryopreservation for biochemical studies