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Wallin, E1, Clatworthy, M1, 2, Pritchard, N1
1Division of Renal Medicine, University of Cambridge, and Addenbrooke’s Hospital,
Cambridge, 2Cambridge Institute for Medical Research, University of Cambridge
BACKGROUND: Fabry disease is an X linked lysosomal storage disorder in which deficiency of
α-Galactosidase A (α-Gal A), leads to accumulation of glycosphingolipids in the vascular
endothelium, kidneys and heart. Males with classical disease present in childhood, however some
individuals with low levels of α-Gal A activity present atypically with adult onset renal
impairment. Screening studies in European patients with established end-stage renal failure
(ESRF) suggest that up to 1.5% of patients have sub-normal α-Gal A levels. These patients, (often
labelled with a diagnosis of ESRF of unknown cause), are at risk of the cardiovascular and
cerebrovascular complications of Fabry disease which might be prevented by enzyme replacement
therapy. Identification of such patients is also important so that “at-risk” relatives may be screened
for disease. Current diagnostic tests (plasma and leucocyte α-Gal A activity assays and genetic
testing) are costly and impractical to apply to large numbers of patients. More recently, a dried
blood spot (DBS) assay has been developed, which overcomes these problems.
AIMS: We wished to assess the efficacy of the DBS assay in a screening study of male patients
with ESRF.
METHODS: All male haemodialysis patients (n=155) at a single UK renal unit (and its three
satellite dialysis units) were screened for low enzyme activity using the DBS assay. Those with a
positive result on the DBS assay were further assessed using plasma and leucocyte enzyme activity
RESULTS: 8 of 155 patients screened had α-Gal A activity below the normal range on DBS
testing (figure 1). α-Gal A activity was re-assessed in plasma in 7 of 8 of these patients (1 patient
died prior to repeat testing) and further confirmed in 4 of 8 patients (3 further patients died prior to
leucocyte testing). α-Gal A activity was at the low end of the normal range in both tests, indicating
false positive results on DBS (figure 2).
CONCLUSIONS: This study is the first screening programme in UK haemodialysis patients
using the DBS test and did not identify any new cases of Fabry disease, thus the frequency of
Fabry disease in UK patients is at the lower end of that described in other European screening
studies. The DBS assay provides a practical and cost effective means of screening large numbers
of patients for low α-Gal A activity, particularly those with ESRF of unknown cause and without
classical symptoms or signs of Fabry disease.
The DBS enzyme assay had a false positive rate of 2.6%, emphasising the need for validation by
alternative testing.