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Assays / Genetic
Enzymes / a-N-Acetylneuraminidase
Principle Of Method:
Hydrolysis of the synthetic substrate 4-methylumbelliferyl-N-acetyl-a-D-neuraminide
at acid pH is followed by measuring the fluorescence of the liberated
4-methylumbelliferone after stopping the reaction with alkaline
buffer.
Uses And Limitations Of The Method:
The enzyme is assayed to diagnose sialidosis
(also called mucolipidosis type I) and galactosialidosis.
These are rare disorders of glycoprotein metabolism in which sialylated
oligosaccharides are excreted in the urine; these can be detected
by urinary oligosaccharide screening as a preliminary diagnostic
procedure. In sialidosis the primary enzyme defect is in neuraminidase
itself, whereas in galactosialidosis it is a "protective" protein
required for the activation of neuraminidase and stabilisation of
b-galactosidase.
This results in low activity of both neuraminidase and a-
galactosidase. The laboratory only offers the assay for routine
diagnosis using cultured fibroblasts because the presence of a second
neuraminidase in leucocytes which is not deficient in sialidosis
and galactosialidosis may render these cells unsuitable. Prenatal
diagnosis is possible by assay of cultured amniotic cells and probably
cultured chorionic villi but the laboratory has not monitored any
at-risk pregnancies. Neuraminidase is an unstable enzyme and special
precautions are needed in its assay.
Specimen Requirements:
Fibroblasts cultured from a skin biopsy are needed. Biopsy
material should be collected aseptically into a sterile bottle
containing tissue culture medium (available from the laboratory),
and sent at room temperature to arrive at the laboratory
within 24 hours. Biopsies for tissue
culture should not be frozen. Fibroblast cultures established
in other laboratories should be sent in plastic 25 cm2
flasks filled with medium.
THE LABORATORY RECOMMENDS USE OF A COURIER
SERVICE OR ROYAL MAIL SPECIAL DELIVERY FOR SENDING ALL SPECIMENS
TO THE LABORATORY.
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Storage Disorders Index
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Assays Available
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