Disclosed are a therapeutic pharmaceutical agent for diseases associated with the decrease in the function of GNE protein, a food composition, and a food additive. The therapeutic pharmaceutical agent is characterized by comprising a compound capable of increasing the quantity of N-acetylneuraminic acid in cells. Examples of the compound to be contained in the therapeutic pharmaceutical agent include N-acetylneuraminic acid, an intermediate produced downstream from N-acetylmannosamine in an N-acetylneuraminic acid biosynthesis pathway, an N-acetylneuraminic acid derivative, an N-acetylmannosamine derivative, an N-acetylneuraminic acid-containing compound, an N-acetylneuraminic acid derivative-containing compound, an N-acetylmannosamine-containing compound, an N-acetylmannosamine derivative-containing compound, an inhibitor of a degrading enzyme for N-acetylneuraminic acid, an inhibitor of a degrading enzyme for N-acetylmannosamine, an inhibitor of a degrading enzyme for the intermediate, and others.