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Assays / Genetic
Enzymes / Heparan
Sulphamidase
Principle Of Method:
Release of 35SO4 from [N-sulphonate-35S]
heparin is measured after low voltage electrophoresis to separate
the inorganic sulphate from substrate. An alternative fluorogenic
substrate, 4-methylumbelliferyl-á-D-sulphoglucosamide, is
available and its use is being evaluated in the laboratory.
Uses And Limitations Of The Method:
The assay is used for determining activity of heparan sulphamidase
which is the primary deficiency in Sanfilippo
disease type A (MPS IIIA).
The natural function of this enzyme is to cleave sulphate groups
from the nitrogen atom of glucosamine residues in heparan sulphate.
In its absence there is storage of heparan sulphate in the tissues
and excess excretion in the urine. The deficiency can be demonstrated
in white cells or fibroblasts, although the former may sometimes
give equivocal results and the SAS laboratory recommends use of
fibroblasts for this assay. MPS IIIA is the most common form of
MPS III in the UK. Prenatal diagnosis is possible by assay of chorionic
villi or cultured amniotic cells; when amniocentesis is performed
investigation of the GAG pattern in the supernatant fluid may assist
in the diagnosis. Heterozygote detection is not routinely offered
although partial deficiency of the enzyme (in fibroblasts only)
can be demonstrated in some carriers.
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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