Mutations at the analogous glycine residues in other human SLC6 transporters have been classified as pathogenic or likely deleterious, thereby conspicuously highlighting the significance of this particular glycine (Table 3): for example, G466R in hCRT‐1 leads to the creatine transporter deficiency (CTD) syndrome [52], which is also manifested by epilepsy and severe intellectual disability. The gene discussed is HCRT; the disease is X-linked creatine transporter deficiency.