Na+/Cl- dependent neurotransmitter transporters are a superfamily of transmembrane proteins that contain 12 membrane spanning regions (1). Specifically, the highly hydrophobic Na+/Cl- dependent glycine transporters (GlyT) are crucial for the termination of neurotransmission at glycinergic synapses (2,3). Two different GlyT genes encode GlyT2 and GlyT1, which exists as two isoforms produced by alternative splicing of the same gene located on human chromosome 1p31.3 (3,4). The GlyT1 gene may be an early marker of neural development and encodes glia-specific transporter proteins (3). Although GlyT1 and GlyT2 are both expressed in the brain and spinal cord, each shows a unique pattern of expression (3,5,6). GlyT1 is found only in the white matter of the CNS, whereas GlyT2 is found in the gray matter of the CNS as well as in macrophages and mast cells in peripheral tissues (3,5). The anatomic distribution of GlyT2 mRNA suggests that glycine may act as a supraspinal neurotransmitter and may function as a chemical messenger outside the CNS (5).