Sialic acid storage disorders (infantile free sialic acid storage disease [ISSD]; OMIM #269920, Salla disease; OMIM #604369) are a spectrum of disorders due to mutations in SLC17A5 (Sialin), which are autosomal recessive neurodegenerative disorders that present as a severe infantile form (ISSD) or as a slowly progressive adult form (Salla disease). The gene discussed is SLC17A5; the disease is free sialic acid storage disease.