Editor—Fabry disease (FD) (OMIM 301500) is an X linked recessive disease resulting from deficiency of the lysosomal hydrolase α-galactosidase A.1 The enzymatic defect leads to the widespread deposition of uncleaved neutral glycosphingolipids in the plasma and lysosomes, especially in vascular endothelial and smooth muscle cells. Initial clinical signs include skin lesions (angiokeratoma), excruciating acral pain, and benign corneal opacities. Progressive glycosphingolipid deposition in the microvasculature of hemizygous males subsequently leads to failure of target organs and to ischaemic complications involving the kidneys, heart, and brain.2 3 Much interest is currently shown in emerging therapies for FD and recent studies have reported that genetic engineering has removed many of the obstacles to the clinical use of enzyme replacement and that infusions of purified α-galactosidase A are safe and biochemically active.4 5 However, clinical and laboratory indicators of benefit are lacking, given the slow course of the disease. This emphasises the need for non-invasive surrogate endpoints to delineate target organ damage and to monitor the efficacy of enzyme replacement therapies.