An autosomal (chromosome or threadlike part of a cell that carries hereditary information in the form of genes) recessive disorder due to a deficiency of sialidase, occurring as two types with differing manifestations.

Type I is of adolescent or adult onset and is characterized by myoclonus, ocular cherry red spot with progressive loss of visual acuity, and storage of sialyloligosaccharides.

Type II is additionally characterized by somatic abnormalities, coarse facies, and dysostosis multiplex.

It occurs as several variants of increasing severity with earlier age of onset; that of infantile onset is characterized also by visceromegaly and mental retardation, and the congenital form is additionally characterized by ascites, hydrops fetalis, facial edema, inguinal hernias, and early death.

Cases of a juvenile form have been shown to be galactosialidosis which is a rare inherited metabolic disorder with multiple symptoms that can include skeletal abnormalities, mental retardation, and progressive neurological degeneration.