Trio-WGS revealed a de novo intragenic 105 kbp tandem duplication (Xp22,13p22.13(18474185_18579246)), which includes exons 2 (the first coding exon) to 5 of CDKL5. CDKL5 deficiency disorder (CDD) is an X-linked developmental and epileptic encephalopathy (DEE) characterized by severe early-onset epilepsy and motor, cognitive, visual, and autonomic disturbances [55]. Here, CDKL5 is linked to developmental and epileptic encephalopathy.