SLC1A4 encodes a sodium-coupled neutral amino acid transporter that plays a critical role in brain serine homeostasis and neurodevelopment. The protein functions as an obligatory amino acid exchanger at the blood-brain barrier, facilitating L-serine transport from blood into the brain 1. SLC1A4 transports various neutral amino acids including L-serine, D-serine, L-alanine, and L-threonine in a bidirectional manner coupled to sodium influx. In the brain, SLC1A4 is essential for maintaining adequate L-serine levels required for protein synthesis, sphingolipid metabolism, and D-serine production for NMDA receptor function 2. The transporter also contributes to cellular redox balance through serine metabolism pathways 34. Pathogenic mutations in SLC1A4 cause a severe neurodevelopmental disorder characterized by microcephaly, spastic tetraplegia, thin corpus callosum, and refractory epilepsy 51. The disease mechanism involves impaired L-serine transport across the blood-brain barrier, leading to decreased brain serine content, accumulation of cytotoxic sphingolipids, and neurodegeneration 1. Early L-serine supplementation has shown therapeutic potential in mouse models, suggesting possible treatment approaches for SLC1A4-related disorders 1.