Search

Spinal muscular atrophy (SMA) is caused by SMN1 gene deletions or mutations, and ALS is the most frequent motor neuron condition in adults. The authors describe three families in which ALS and SMA coexist. The authors found that no SOD1 mutation was found within these families; all three ALS cases had at least two SMN1 copies; and an abnormal SMN1 gene locus did not explain the co-occurrence of these two motor neuron disorders in these families.

The etiology of amyotrophic lateral sclerosis remains unknown in the majority of cases. Homozygous SMN1 (survival motor neuron) gene deletion causes spinal muscular atrophy, and SMN2 gene deletions are possible risk factors in lower motor neuron disease. We studied SMN1 and SMN2 genes copy numbers in 167 amyotrophic lateral sclerosis patients and in 167 matched controls. We noted that 16% of amyotrophic lateral sclerosis patients had an abnormal copy number of the SMN1 gene (1 or 3 copies), compared with 4% of controls. An abnormal SMN1 gene locus may be a susceptibility factor for amyotrophic lateral sclerosis.