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Assays / Genetic
Enzymes / Aspartylglucosaminidase
Principle of Method:
Hydrolysis of the substrate L-aspartic acid â-(7-amido-4-methylcoumarin)
to aspartic acid and 7-amino-4-methylcoumarin is followed by measuring
the fluorescence of the latter molecule. This is a more convenient
method than that using the natural substrate aspartylglucosamine
which requires assay of released N-acetylglucosamine using the Morgan-Elson
reaction.
Uses And Limitations Of The Method:
This enzyme is deficient in aspartylglycosaminuria,
a disorder of glycoprotein degradation, occurring primarily in Finland
but rare elsewhere. Initial biochemical suspicion of the disorder
arises if aspartylglucosamine and related substances are observed
in urine by oligosaccharide screening: the staining pattern with
resorcinol is the most characteristic. The diagnosis is confirmed
by assaying plasma, serum, white cells or cultured fibroblasts.
Prenatal diagnosis is possible by analysis of chorionic villi or
amniotic cells. Assay of the enzyme using plasma is sometimes included
in the laboratory's lysosomal screening routine for patients with
neurological degeneration with or without dysmorphia.
Specimen Requirements:
For preliminary testing, blood. 5 ml lithium heparin (orange
capped tube) unseparated and unfrozen. Send at room temperature
to arrive at the laboratory
within 24h of venepuncture. For follow-up, fibroblasts cultured
from a skin biopsy may be 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 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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