MONDO_0018097 (infantile spasms) is a rare epilepsy syndrome characterized by onset of epileptic spasms in infants between 2 and 12 months of age, and rarely up to 24 months. Infants may have no antecedent history, or a history reflecting the underlying cause. The classical triad of epileptic spasms, hypsarrhythmia and developmental stagnation or regression is historically referred to as West syndrome. Also known as: IESS, West syndrome, West's syndrome, infantile epileptic spasms syndrome, infantile spasms syndrome, intellectual disability-hypsarrhythmia syndrome.