Familial amyotrophic lateral sclerosis: Amyotrophic lateral sclerosis (ALS) in which there a family history of the disease. Familial ALS constitutes 5 to 10% of all cases of ALS. There are a number of different types of familial ALS.

They are known as ALS1, ALS2, and so on. ALS1 -- caused by mutation in the superoxide dismutase-1 gene (SOD1) on chromosome 21q22.1. About 15 to 20% of familial ALS is type 1 (ALS1). Sporadic cases of ALS are sometimes due to new mutation in the SOD1 gene. ALS2 -- juvenile-onset ALS caused by mutation in the gene encoding alsin on chromosome 2q33; ALS3 -- adult-onset ALS due to mutation in a gene on chromosome 18q21; ALS4 -- juvenile-onset disease with no bulbar involvement due to mutations in a gene on chromosome 9q34; ALS5 -- due to mutations in a gene on chromosome 15q15.1-q21.1; ALS6 -- due to mutations in a gene on chromosome 16q12; ALS7 -- due to mutations in a gene on chromosome 20ptel; ALS8 -- due to mutations in a gene on chromosome 20q13.33. ALS1, ALS3, ALS4, ALS6, ALS7, and ALS8 are inherited in an autosomal dominant manner while ALS2 and ALS5 are inherited in an autosomal recessive manner.