MedGen

CHD2-related neurodevelopmental disorders are characterized by early-onset epileptic encephalopathy (i.e., refractory seizures and cognitive slowing or regression associated with frequent ongoing epileptiform activity). Seizure onset is typically between ages six months and four years. Seizure types typically include drop attacks, myoclonus, and rapid onset of multiple seizure types associated with generalized spike-wave on EEG, atonic-myoclonic-absence seizures, and clinical photosensitivity. Intellectual disability and/or autism spectrum disorders are common. [from GeneReviews]

EEG with generalized sharp transient waves of a duration less than 80 msec. [from HPO]

An extremely rare form of hereditary episodic ataxia with characteristics of recurrent episodes of vertigo and ataxia lasting several hours. [from SNOMEDCT_US]