Definition

Spinal muscular atrophies (SMAs) are a wide group of genetic disorders characterized by primary degeneration of anterior horn cells of the spinal cord, resulting in progressive muscle weakness. The most common form of spinal muscular atrophy is childhood proximal SMA. Other forms of SMAs include X-linked recessively inherited bulbospinal SMA, distal SMAs, scapuloperoneal SMAs, and others such as facioscapulohumeral, scapulohumeral, oculopharyngeal, and Ryukyuan SMAs.

Description

SMAs present with diverse symptoms and differ in age of onset, mode of inheritance, distribution of muscle weakness, and progression of symptoms.

Childhood proximal SMA is subdivided into three clinical groups: type I, type II, and type III SMA. SMA type IV designates adult form of proximal SMA. Although it is now apparent that the phenotype of SMA associated with mutations of the survival motor neuron (SMN1) gene...