Methods are disclosed for treating a subject with a vascular or cardiac disorder associated with oxidative stress. Methods are disclosed for treating a subject with GNE myopathy that has impaired cardiac function. These methods include administering to the subject a therapeutically effective amount of a sialic acid precursor, sialic acid, or one or more sialylated compounds, mannosamine, N-acetyl mannosamine or a derivative thereof. In other embodiments, methods are disclosed for detecting a disorder associated with oxidative stress.