Childhood onset SMA

Childhood onset SMA can be classified into three types,
distinguished on the basis of clinical severity and age of onset.
In type I (Werdnig–Hoffman disease), onset occurs within the
first six months of life and children usually die within two years.
In type II (intermediate type Dubowitz disease) onset is before
18 months with death occuring after two years. In type III
(Kugelberg–Welander disease), the disease has a later onset
and milder, chronic cause with affected children achieving
ambulation.