Enzyme Replacement Therapy for Fabry Disease

Abstract

Fabry disease is a progressive and life-threatening glycolipid storage disorder affecting both males and females. The primary driver of the disease is the accumulation of glycolipids (globotriaosylceramide [GL-3]) in a variety of cell types, including vascular endothelial cells, a range of renal cell types, cardiomyocytes and neurons, which is caused by deficient activity of the lysosomal enzyme, alpha-galactosidase. The disease typically presents during childhood or adolescence. First manifestations reflect involvement of small nerve fibres of the peripheral and autonomic nervous systems. With age, severe complications involving the kidneys, heart and brain cause considerable morbidity and premature death. Outside the US, enzyme replacement therapy (ERT) with agalsidase alfa 0.2 mg/kg every other week (EOW) and agalsidase beta 1.0 mg/kg EOW is available for the treatment of patients with Fabry disease, while agalsidase beta 1.0 mg/kg EOW is the only approved drug in the US. To analyse the evidence for ERT, a systematic review of the literature was performed to identify prospectively designed randomized, controlled trials (RCTs) and open-label studies on the efficacy of agalsidase alfa and agalsidase beta. MEDLINE and EMBASE databases were searched; inclusion criteria for the systematic review were prospectively designed clinical studies evaluating ERT with quantifiable endpoints: double-blind and open-label studies were eligible. Exclusion criteria were review articles, case reports, case studies, letters to the editor and articles based on registry data (Fabry Outcome Survey or Fabry Registry). In addition, any studies with a retrospective design or data based on post hoc analyses were excluded. The evidence was reviewed with respect to the clinical benefits of ERT at the level of the end organ. A total of 9 RCTs and 23 open-label studies were identified for inclusion. The efficacy of ERT in Fabry disease has been measured against a variety of endpoints, the majority of which were subclinical parameters rather than clinical outcomes. Plasma levels of GL-3 together with accumulation in the kidney, heart and skin were the most commonly studied endpoints, followed by renal endpoints of proteinuria and glomerular filtration rate, whereas cardiac and neurological endpoints were not commonly studied. To date, only one RCT with ERT defined hard clinical outcomes in the form of cardiac, renal or cerebrovascular events, or death as its primary endpoint. The currently available data from prospective RCTs and open-label studies in patients with Fabry disease are more robust for ERT at a dose of 1 mg/kg EOW than a dose of 0.2 mg/kg EOW, although the beneficial effects of ERT with either dose or preparation are variable.