[Juvenile and adult forms of spinal muscular atrophies]

We propose a classification system for spinal muscular atrophies (SMA) based on the distribution of clinical signs, paresis and atrophy, as well as on the location of the responsible gene and the resulting enzyme deficiency, whenever these are known. This highly practical classification system encompasses three large SMA groups, as follows. A) Generalized forms, many of which are hereditary, are generally transmitted in a recessive autosomal manner. The course of disease is more severe when symptoms manifest early. Patients whose symptoms first occur after the first year of life often reach adolescence and even adulthood, confirming a highly apparent congruence of intermediate and pseudomyopathic juvenile forms. The same genetic defect, deletion in the 5q11-13.3 locus, that is responsible for acute infantile SMA has been demonstrated in both the aforementioned forms. B) Focal forms are restricted and often isolated cases; when they are hereditary, the genetic profile is highly heterogeneous. Though the disease will not necessarily evolve, it may progress to a generalized form. Focal forms may be symetric, assymetric, spinal-bulbar or multisegmental. The genetic abnormality has been identified for only some forms, such as chronic bulbar-spinal amyotrophy linked to the X-chromosome, at whose location, Xq11, the androgenic receptor is found. C) Amyotrophic lateral sclerosis (ALS) manifests clinically in a variety of ways and may be isolated, familial, juvenile or associated. Familial ALS is related to a gene defect in the 21q22.1 location that codifies for the superoxide dismutase enzyme. One juvenile form of ALS is related to a defect in the 2q33-35 chromosome. Any type of SMA can be related to degenerative neuronal disease of the central nervous system, especially juvenile ALS with generalized SMA, although such a link is at present merely an attractive hypothesis. Specific bibliographic references are given for each SMA form. Figures are provided to illustrate most of the SMA forms included in this classification system, the patients being at this time older adolescents and adults whose disease has been in evidence over many years.