The genetic heterogeneity of spinal muscular atrophy (SMA).

The clinical picture of the spinal muscular atrophy varies greatly with respect to age of onset, speed of progression, severity and distribution of muscular atrophy, weakness and contractures, yet cases occurring within a family usually show concordant clinical features. Thus, genetic heterogeneity has to be assumed. This is supported by the various genetic transmission patterns (autosomal dominant, recessive, X-linked recessive) found by accurate pedigree analysis.