The proband (patient 1), a 25-year-old woman, was the product of normal pregnancy and delivery. Her parents were first cousins from Lebanon. She sat at 6 months and crawled at 12 months. At age 3, she was noted to have developmental delay, hypotonia, and ataxia. The following year, she had a febrile illness and suspected absence seizure. EEG showed 4–5 Hz spike and slow wave complexes and she was treated with sodium valproate. At age 6, seizure frequency increased but improved with the addition of ethosuximide. Brain MRI at age 10 revealed increased T2 signal in both thalami and upper brainstem (figure). Serum and urinary amino acids, white blood cell lysosomal enzymes, serum lactate and pyruvate, liver function, and ammonia were normal. CSF neurotransmitters, glucose, and lactate were normal, although GABA was not measured. Her condition then remained static with occasional absence seizures. At age 22, she developed paroxysmal episodes of chorea in the neck, arms, and trunk associated with drowsiness, triggered by fever or hot weather (video 1). These occurred 4–5 times a year, lasting from 1 to 10 minutes. In all episodes, she remained responsive to verbal stimuli. Prolonged interictal video EEGs showed intermittent 4–6 Hz generalized epileptiform discharges, although no motor events were recorded.