Enzyme replacement therapy in Fabry disease was initiated in 2001. In a significant proportion of patients, the apparent removal of stored glycosphingolipid from the endothelial cells does not prevent progression of vascular disease. Shu et al. show a link between accumulation of globotriaosylceramide in the endothelial cells and 3-nitrotyrosine formation, indicating endothelial nitric oxide synthase uncoupling. 3-Nitrotyrosine will be useful to better understand Fabry vasculopathy, and to evaluate additional therapeutic interventions targeting oxidative stress.