SLC6A8 (solute carrier family 6 member 8), also known as CT1 (creatine transporter 1), CRT or CRTR, is a 635 amino acid multi-pass plasma membrane protein that belongs to the sodium/neurotransporter (SNF) family. Expressed in a variety of tissues including kidney, skeletal muscle, heart, brain, prostate, testis and colon, SLC6A8 functions to transport creatine into and out of cells, specifically those found in brain and muscle tissue. Creatine, an organic acid, occurs naturally and is essential for supplying the energy needed for proper muscle and nerve function. Defects in the gene encoding SLC6A8 lead to cerebral creatine deficiency and are the cause of X-linked creatine deficiency syndrome, a rare disorder characterized by facial anomalies, seizures and mental retardation. Multiple isoforms of SLC6A8 exist due to alternative splicing events.