SLC17A5 and neurodegenerative disease: Lysosomal free sialic acid storage disorder (FSASD) is a rare autosomal recessive, neurodegenerative disease caused by biallelic variants in SLC17A51–3, which encodes sialin, a lysosomal membrane transporter responsible for the efflux of sialic acid and other acidic hexoses from the lysosome to the cytosol4–8.