Rationale: Mutations in the TBC1D24 gene were first reported in a family with infantile onset prolonged myoclonic seizures. We describe 11 children (1 pair of siblings and 1 set of twins) with intractable infantile myoclonic epilepsy who had TBC1D24 mutations identified on genetic testing in four pediatric epilepsy centers. Common factors in the clinical presentation are described which should prompt practitioners to test for a TBC1D24 associated epilepsy syndrome is described.  
Results:  Seven were girls and 4 boys.  All had early infantile onset of prolonged, focal myoclonic seizures which shifted from side to side, not associated with loss of awareness and not associated with any ictal EEG change. Five had sensorineural hearing loss. All walked by age 2 and all children without hearing loss had several single words by age 2. Initial development was normal but later the developmental trajectory slowed.  Seven children developed ataxia around age 2 years. Older children and adolescents had moderate to severe intellectual disability and short stature. Initial imaging was normal but later 5 developed cerebellar abnormalities.Conclusions:  Eleven patients with TBC1D24 mutations are described who presented with a characteristic syndrome of early infantile prolonged focal myoclonic seizures. The normal early development, maintained awareness during seizures and lack of ictal EEG correlate distinguished these cases from other early infantile epileptic encephalopathies.  With age, cerebellar findings, developmental stagnation and acquired short stature became evident. Recognition of this distinctive presentation should prompt evaluation for TBC1D24 mutation to avert unnecessary testing, help determine prognosis and guide genetic counseling.