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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, and 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, corneal clouding, 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.
Diagnosis of GM1 gangliosidosis, Morquio B disease, and galactosialidosis
Results <5.0 nmol/h/mL in properly submitted specimens are consistent with beta-galactosidase deficiency (GM1 gangliosidosis and Morquio B disease). Further differentiation between GM1 and Morquio B is dependent on the patient's clinical findings.
Normal results (> or =5.0 nmol/h/mL) are not consistent with beta-galactosidase deficiency.
This test cannot reliably determine carrier status.
This test does not differentiate between GM1 gangliosiosis and Morquio B disease.
> or =5.0 nmol/h/mL
An interpretive report will be provided.
1. Suzuki Y, Sakuraba H, Oshima A: Chapter 151: Beta-galactosidase deficiency In The Metabolic Basis of Inherited Disease. Vol. 3. Eighth edition. Edited by CR Scriver, AL Beaudet, WS Sly, D Valle. New York, McGraw-Hill Book Company, 2001
2. Chamoles NA, Blanco M, Gaggioli D, Casentini C: Hurler-like phenotype: enzymatic diagnosis in dried blood spots on filter paper. Clin Chem 2001;47:2098-2102