CDKL5 and early-infantile DEE: Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD), catalogued in online mendelian inheritance in man (OMIM ID: 300203, 300672) [1], is a severe neurodevelopmental disorder that is also known as early infantile epileptic encephalopathy, which is classified as a developmental and epileptic encephalopathy (DEE) [2,3].