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Assays / Genetic
Enzymes / Ceramidase
Principle of Method:
Hydrolysis of radiolabelled ceramide (labelled in the fatty acid
moiety) at acid pH is followed by measuring the radioactivity in
the fatty acid released after solvent partitioning and thin-layer
chromatography. The ceramide for the assay is prepared chemically
in the laboratory by condensation of a [14C]
fatty acid (palmitic acid in the current batch) with sphingosine.
Uses and Limitations of the Method:
Deficiency of acid ceramidase is the primary defect in Farber
disease (lipogranulomatosis). It is
a rare disorder and the SAS laboratory is one of only a few in the
world offering the assay. Unusually, activity of acid ceramidase
is higher in normal leucocytes than in fibroblasts, and the former
cells are certainly the material of choice for making the diagnosis.
Prenatal diagnosis of the disease is possible by assay of chorionic
villi or amniotic cells, but the SAS laboratory does not offer this
at present. Two other ceramidases, with neutral and alkaline pH
optima, respectively, do not appear to be affected in Farber disease.
There are no characteristic storage substances in urine that assist
in making the diagnosis, but demonstration of excess ceramide in
a biopsy of one of the subcutaneous nodules would provide strong
evidence for the disease.
Specimen Requirements:
Blood. 5 ml lithium heparin (orange capped tube)
unseparated and unfrozen. Send at room temperature to arrive at
the laboratory
within 24h of venepuncture.
THE LABORATORY RECOMMENDS USE OF A COURIER
SERVICE OR ROYAL MAIL SPECIAL DELIVERY FOR SENDING ALL SPECIMENS
TO THE LABORATORY.
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