Spinal muscular atrophies of childhood and adolescence

The term spinal muscular atrophy (SMA) refers to a clinically and genetically heterogeneous group of diseases characterized by degeneration and loss of anterior horn cells in the spinal cord and sometimes also in the brainstem nuclei, resulting in muscle weakness and atrophy. The autosomal recessive infantile SMA (SMA 5q) is responsible for about 80-90% of all SMA cases and is classified according to clinical severity into types I-III. Because more than 90% of patients show a homozygous deletion of the SMN1 gene, molecular genetic testing has become the most important diagnostic tool. Improved methods for heterozygosity testing have also become available, allowing a reliable risk stratification of relatives and their spouses. With increasing knowledge of other genes that cause anterior horn cell degeneration, our understanding of the pathogenesis and possible therapeutic interventions will improve. Despite promising results from genetic studies, preliminary clinical trials, and experiments with animal models, a curative treatment of SMA is not yet available.