Methodology of a Natural History Study of a Rare Neurodevelopmental Disorder: Alternating Hemiplegia of Childhood as a Prototype Disease.

Here, we describe the process of development of the methodology for an international multicenter natural history study of alternating hemiplegia of childhood as a prototype disease for rare neurodevelopmental disorders. We describe a systematic multistep approach in which we first identified the relevant questions about alternating hemiplegia of childhood natural history and expected challenges. Then, based on our experience with alternating hemiplegia of childhood and on pragmatic literature searches, we identified solutions to determine appropriate methods to address these questions. Specifically, these solutions included development and standardization of alternating hemiplegia of childhood-specific spell video-library, spell calendars, adoption of tailored methodologies for prospective measurement of nonparoxysmal and paroxysmal manifestations, unified data collection protocols, centralized data platform, adoption of specialized analysis methods including, among others, Cohen kappa, interclass correlation coefficient, linear mixed effects models, principal component, propensity score, and ambidirectional analyses. Similar approaches can, potentially, benefit in the study of other rare pediatric neurodevelopmental disorders.