Juvenile myoclonic epilepsy (JME), also known as Janz syndrome or impulsive petit mal, is a form of hereditary, idiopathic generalized epilepsy,[1] representing 5–10% of all epilepsy cases.[2][3][4] Typically it first presents between the ages of 12 and 18 with myoclonic seizures (brief, involuntary, single or multiple episodes of muscle contractions caused by abnormal excessive or synchronous neuronal activity in the brain).[5] These events typically occur after awakening from sleep, during the evening or when sleep-deprived. JME is also characterized by generalized tonic–clonic seizures, and a minority of patients have absence seizures.[6] It was first described by Théodore Herpin in 1857. Understanding of the genetics of JME has been rapidly evolving since the 1990s, and over 20 chromosomal loci and multiple genes have been identified.[7] Given the genetic and clinical heterogeneity of JME some authors have suggested that it should be thought of as a spectrum disorder.