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.
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.