Spinal muscular atrophy

Spinal muscular atrophy (SMA) is a neuromuscular disease characterized by degeneration of motor neurons, resulting in progressive muscle atrophy and paralysis. The most common form of SMA is caused by mutations of the SMN gene, that encodes the SMN protein, which regulates snRNP assembly. Four types of SMA are recognized depending on the age of onset and the severity of the disease: type I (Werdning-Hoffman), type II (intermediate), type III (Kugeleberg-Welander) and type IV (adult form). Other forms of spinal muscular atrophy are caused by mutation of other genes, some known and others not yet defined.