Clinical implications of the genetics of ALS and other motor neuron diseases

Genetic mutations have been identified in the major motor neuron diseases, including AZ,S, spinal muscular atrophy, bulbospinal muscular atrophy (Kenn edy's disease), the hereditary spastic paraplegias, and rarer conditions su ch as GM2 gangliosidosis (hexosaminidase A deficiency). These include mutat ions in the SOD1 gene, deletions of the telomeric copy of the SMN gene, exp ansions of the trinucleotide repeat region in the first exon of the androge n receptor gene, other rare mutations, and diseases where linkage has been established but the gene not identified. Identification of one of these gen etic abnormalities will allow specific diagnosis in patients. Because cure is not yet available, presymptomatic testing is seldom indicated; in such c ases, careful counseling is appropriate.