Sialin, the protein coded by SLC17A5 is a membrane transporter that exports free sialic acids that have been cleaved off of cell surface lipids and proteins from lysosomes. Mutations in this gene cause sialic acid storage diseases, including infantile sialic acid storage disorder and Salla disease, an adult form. Sialic acid storage disease (SASD) is an autosomal recessive neurodegenerative disorder characterized by hypotonia, cerebellar ataxia and mental retardation. They can be caused by defects in the metabolism of sialic acid which results in increased urinary excretion of unconjugated sialic acid, specifically N-acetylneuraminic acid.