X-linked Creatine Transporter Deficiency (CTD) (see Fig. 1) was chosen as an ideal candidate for manual curation because it is a monogenic disorder with a phenotype largely dependent upon the function of a single gene, SLC6A8, at a hemizygous location [14] on the X chromosome. This evidence concerns the gene SLC6A8 and X-linked creatine transporter deficiency.