Can be due to a nonprogressive or a progressive degenerative neurological disorder.
Infants with nonprogressive disorders show signs of developmental delay, but maintain their developmental trajectory curve.
Infants with progressive neurologic disorders reach a plateau and then lose their developmental skills.
Progressive and nonprogressive neurological disorders may overlap and make it difficult to distinguish between the two types of developmental disorders.
The passage of time and careful follow-up allows the differentiation between the two entities.
Developmental delay occurs and 1-3% of children and can be isolated or global.