Epilepsy Phenotype and EEG Finding of Rhythmic High-Amplitude Delta With Superimposed Spikes (RHADS) in Succinate...

Succinate dehydrogenase (SDH) serves a dual function as complex II of the electron transport chain and an enzyme of the tricarboxylic acid cycle. Pathogenic variants in subunits of SDH result in diverse clinical presentations, including typically autosomal recessive neurodegenerative disorders. Biallelic variants in the SDHA subunit most often cause Leigh syndrome. However, epilepsy phenotypes of these patients are ill-defined and there is only one prior report of epilepsy in a patient with SDHA deficiency. Here we report the seizure and EEG phenotypes of three autosomal recessive SDHA patients with refractory epilepsy, two of whom are siblings. These patients exhibit multiple seizure types and a variety of EEG findings, including a patient with rhythmic high-amplitude delta with superimposed spikes (RHADS), a finding closely associated with polymerase gamma (POLG)-related disorders.