SLC36A4 encodes a high-affinity amino acid transporter that functions as a uniporter mediating the transport of neutral amino acids including L-tryptophan, proline, and alanine 1. The transporter operates via sodium-independent, electroneutral facilitated diffusion with exceptionally high substrate affinities (Km values of 1.72 μM for tryptophan and 3.13 μM for proline) 1. SLC36A4 regulates amino acid pools in retinal pigmented epithelial cells and modulates mTORC1 signaling pathways, with increased expression leading to cytoplasmic retention of transcription factors TFEB and TFE3, thereby suppressing lysosomal function 2. The transporter plays important roles in placental nutrient transport, as maternal proline supplementation increases placental Slc36a4 expression and enhances fetal development 3. Disease relevance includes associations with age-related macular degeneration, where dysregulated SLC36A4 contributes to impaired lysosomal function in retinal pigmented epithelium 2, and potential involvement in cancer, with somatic variants identified in lung adenocarcinoma patients 4. The transporter has also been identified as an autoantigen target in pemphigus vulgaris 5.