The children suffer frequent fits of many different types, and experience gradual mental deterioration. Infantile spasms often evolve into Lennox-Gastaut syndrome, and the age of onset is from 1 to 8 years, peaking at 3 to 5 years. The prognosis for children with Lennox-Gastaut syndrome is bleak. Lennox-Gastaut syndrome is characterised by multiple types of fit. As well as drop attacks, these are likely to include atypical absence fits and massive myoclonic jerks.
Myoclonic jerks are the violent jerking of one or more limbs.