N-acetylmannosamine (ManNAc) is a small uncharged physiological molecule that crosses membranes readily and is the natural precursor of intracellular sialic acid synthesis. NHGRI investigators discovered that ManNAc can be used for therapeutic purposes, including treating certain kidney diseases (e.g., those involving proteinuria and hematuria), resulting primarily or secondarily from hyposialylation (lack of sialic acid). Notably, ManNAc can also be used to treat diabetic nephropathy or diabetes.