biostudies-literatureSaldaris JNINDS NIH HHSNIHInternational Foundation for CDKL5 Research541-547https://www.ebi.ac.uk/biostudies/studies/S-EPMC9149062biostudies-literatureUnknown37(6)Pathogenic variants in the <i>CDKL5</i> gene result in CDKL5 deficiency disorder (CDD), which is characterized by early-onset epilepsy, severe developmental delay, and often, cortical visual impairment. Validated clinical outcome measures are needed for future clinical trials to be successful. This study aimed to adapt the Rett Syndrome Hand Function Scale for CDKL5 deficiency disorder and evaluate its feasibility, acceptability, content validity, and reliability. Consultation with a cortical visual impairment experienced specialist and the Consumer Reference Group informed modifications to the instructions of the Rett Syndrome Hand Function Scale for children with CDKL5 deficiency disorder (CDD-Hand). Eighty-six families registered with the International CDKL5 Disorder Database provided vJournal of child neurologyInitial Validation and Reliability of the CDKL5 Deficiency Disorder Hand Function Scale (CDD-Hand).PMC9149062U01 NS1143121U01NS114312-01A1Demarest SSaldaris JBenke TAJacoby PDowns JLeonard HMarsh EDfalseInitial Validation and Reliability of the CDKL5 Deficiency Disorder Hand Function Scale (CDD-Hand).Pathogenic variants in the <i>CDKL5</i> gene result in CDKL5 deficiency disorder (CDD), which is characterized by early-onset epilepsy, severe developmental delay, and often, cortical visual impairment. Validated clinical outcome measures are needed for future clinical trials to be successful. This study aimed to adapt the Rett Syndrome Hand Function Scale for CDKL5 deficiency disorder and evaluate its feasibility, acceptability, content validity, and reliability. Consultation with a cortical visual impairment experienced specialist and the Consumer Reference Group informed modifications to the instructions of the Rett Syndrome Hand Function Scale for children with CDKL5 deficiency disorder (CDD-Hand). Eighty-six families registered with the International CDKL5 Disorder Database provided v2022-01-01T00:00:00Z2022 May2025-04-22T11:48:59.94Z2025-04-06T00:07:40.64ZS-EPMC91490623542214110.1177/08830738221091044