SOD1 and amyotrophic lateral sclerosis: Compared to the dominant haplotype, the recessive haplotype harbors a mutation in a small non-coding region across SOD1. Remarkably, ALS did not develop among 139 D91A heterozygote individuals who had the recessive haplotype and had reached the age of risk for developing ALS, suggesting a potential protective effect of this additional mutation in non-coding regions.