While a net change in superoxide levels is a balance between production and dismutation of superoxide (Csiszar et al., 2007; Alom-Ruiz et al., 2008), endothelial dysfunction in contexts such as hypertension, atherosclerosis, and aging is often due to increases in NAD(P)H oxidase activity (Dworakowski et al., 2006, 2008b; Heistad et al., 2009). Here, FMO5 is linked to atherosclerosis.