Slc6a9, which encodes glycine transporter 1 (GLYT1), plays a crucial role in regulating glycine neurotransmission by removing glycine from the synaptic cleft. It is involved in both inhibitory and excitatory neurotransmission pathways, and is closely associated with glutamate/glycine co-activated NMDA receptors [3].

In an oocyte-specific Slc6a9 knockout mouse model, null oocytes failed to develop glycine transport activity during meiotic maturation. Embryos derived from these null oocytes could not counter hypertonic stress, indicating that Slc6a9 is required for glycine transport and protection against increased osmolarity in mouse eggs and early embryos [2].

In Slc6a9 mutant zebrafish, there was discoordination of spinal neural activities and pronounced lateral spinal curvature, resembling the phenotype of human adolescent idiopathic scoliosis (AIS) patients. Variants of Slc6a9 reduced glycine-uptake activity, leading to increased extracellular glycine levels and aberrant glycinergic neurotransmission, suggesting a neuropathic origin for AIS [1].

In conclusion, Slc6a9 is essential for glycine transport and maintaining normal neurotransmission. Studies using gene-knockout models, such as in mice and zebrafish, have revealed its role in early embryo development and in the pathogenesis of diseases like AIS. Understanding Slc6a9 function provides potential avenues for early diagnosis and intervention in related diseases.