All of these findings support the importance of identifying an etiology to help guide treatment, but also to provide information on expected seizure and developmental outcomes, but still raise the question of whether there actually is a subset of children who truly have no identifiable etiology for spasms. In the 39 infants who had normal development prior to IS onset and achieved IS freedom with first medication, 64.1% had normal development at last follow-up. It is possible that this very small group is the group that truly has IS of unknown etiology. I remain hopeful that further advances in genetic and imaging evaluations will allow us to identify this group and better counsel parents on expected outcomes.