Beyond Seizures as an Outcome Measure: A Global Severity Scoring System for CDKL5 Deficiency Disorder

Background: CDKL5 deficiency disorder (CDD) is a rare developmental and epileptic encephalopathy (DEE) associated with multiple impairments and comorbidities. Outcome measures for disease-modifying clinical trials for DEEs should measurably capture a spectrum of caregiver priorities and be externally validated. Methods: The International CDKL5 Clinical Research Network was the data source for this observational study. A Structural Equation Model was constructed with latent, exogenous variables related to observed clinical features to calculate a global severity score from the following assessments: the CDKL5 Clinical Severity Assessment-Clinician and -Caregiver, Communication and Symbolic Behavior Scales Developmental Profile Infant Toddler Checklist and the Sleep Disturbance Scale for Children. Quantitative EEG power was measured as a biomarker. The Quality of Life Inventory—Disability measured quality of life. Results: Acceptable fit statistics for models were obtained using data from 206 subjects (median [range] age 6.8 [3 months to 40] years). Motor and communication measures were the most important weighted contributors to the global severity score which correlated well with the biomarker and quality of life to support external validation. Conclusions: The resultant global severity score provided evidence that the assessments formed a coherent set of measures that reliably and meaningfully captured the diversity of severity in CDD. The models illustrated how the symptoms form a measurable network of relationships which may be suitable as an outcome measure for CDD and DEEs more broadly in clinical trials.