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 abnormal levels of protein in the urine and/or blood in the urine), resulting primarily or secondarily from hyposialylation (deficiency of sialic acid). Notably, ManNAc can also potentially be used to treat diabetic nephropathy.