Spinal muscular atrophy A preliminary result toward new therapy

Spinal muscular atrophy (SMA) is an anterior horn cell disease characterized by severe muscle atrophy and weakness,(1) traditionally divided into 4 subtypes.(2) Type I SMA (Werdnig-Hoffman disease) is the most severe form, associated with extreme weakness and hypotonia since birth or early infancy. These patients never sit independently. In most cases, respiratory muscle dysfunction results in early death within the first 2 years of life. Types II and III SMA have a milder course. Children with type II SMA (intermediate type) can sit but cannot walk independently. Children with type III SMA (Kugelberg Welander) are often misdiagnosed with myopathy or muscular dystrophy. They present with proximal weakness and are able to walk independently for at least a few years. The mildest variant is adult-onset type IV SMA, in which patients can ambulate in adulthood.