SMN1 gene, but not SMN2, is a risk factor for sporadic ALS

Abstract

Background: SMN1 gene deletions cause spinal muscular atrophy, and SMN2 gene deletions have been associated with sporadic lower motor neuron diseases.

Objectives: To study the frequency of abnormal SMN1 gene copy numbers and to determine whether SMN2 gene modulates the risk of amyotrophic lateral sclerosis (ALS) or the duration of evolution.

Method: The authors studied SMN1 and SMN2 genes in 600 patients with sporadic ALS and 621 controls using a quantitative PCR method.

Results: The authors found an association of ALS with an abnormal copy number (one or three copies) of SMN1 gene (p < 0.0001) with an OR of 2.8 (1.8 to 4.4, 95% CI). There was no association with SMN2 copy numbers and no effect of SMN2 copies on the duration of evolution in ALS independently of SMN1 copy number.

Conclusion: Abnormal SMN1 gene copy numbers are a genetic risk factor in sporadic amyotrophic lateral sclerosis. There was no modulator effect of the SMN2 gene.