Familial amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is inherited in ten percent of cases as a Mendelien trait. Familial ALS (FALS) is genetically heterogeneous and transmitted either as an autosomal dominant (DFALS) or an autosomal recessive (RFALS) trait. Fifteen percent of DFALS families have mutations in the gene for Cu,Zn superoxide dismutase (SOD1) which is coded on chromosome 21. These mutations result in decreased SOD1 activity and shortened half-life of the protein in most instances. Several observations suggest that the degeneration of motor neurons in DFALS is caused by the gain of a novel toxic function by mutated SOD1 rather than by the decrease of SOD1 activity. Possible mechanisms of the novel neurotoxic function of mutated SOD1 are discussed. The role of eventual neurofilament involvement in the pathogenesis of ALS is also discussed. The locus for one form of RFALS has been mapped to chromosome 2q33. FALS can also be associated with dementia and the gene locus for one form of hereditary ALS-dementia syndrome maps to chromosome 17q21-22.