An inborn disorder of N-acetylneuraminic (sialic) acid storage characterized mainly by massive excretion of free sialic acid, severe psychomotor deterioration, and ataxia. The term Salla disease denotes the Finnish type of sialic acid storage disease named for the geographic area where the kindred lived. The infantile form has no ethnic predilection and is associated with severe visceral involvement, dysostosis multiplex, psychomotor retardation, and early death. The Finnish type has onset at 12-18 months of age with deterioration in the second decade.