SLC17A5 encodes sialin, a lysosomal membrane transporter responsible for exporting free sialic acid from lysosomes 1. The protein functions as a sialic acid:proton symporter and also transports D-glucuronate and other carbohydrate derivatives across the lysosomal membrane. Loss-of-function mutations in SLC17A5 cause free sialic acid storage disorders (FSASDs), including Salla disease and infantile sialic acid storage disorder, characterized by impaired lysosomal sialic acid efflux leading to cellular dysfunction and progressive neurological impairment 21. Beyond its primary role in lysosomal transport, emerging evidence implicates SLC17A5 in broader disease mechanisms. Genetic studies identified SLC17A5 variants as a novel Parkinson's disease susceptibility locus, with heterozygous carriers showing increased risk 3. Functional screening in Drosophila confirmed that knockdown of the SLC17A5 homolog enhances α-synuclein-induced neurodegeneration 4. Additionally, sialin mediates macrophage polarization and metabolic homeostasis through a sialin-cathepsin L-Nrf2 pathway, with dysregulation observed in metabolic dysfunction-associated steatohepatitis patients 5. Transcriptomic analyses identified SLC17A5 as differentially expressed between sexes in multiple sclerosis 6. Recent therapeutic advances include CRISPR base editing successfully correcting the founder FSASD variant c.115C>T with significant free sialic acid reduction 1.