SLC6A8 and atypical Rett syndrome: One known mutation in the OTC gene (Table 2) and seven variants of unknown significance in six genes were detected with XL disease inheritance including DCX (lissencephaly), PDHA1 (PDH deficiency), ABCD1 (X-linked adrenoleukodystrophy), MECP2, CDKL5 (Rett syndrome), and SLC6A8 (creatine transport defect) (Additional file1: Tables S2 and Additional file4: Table S3).