One way to target the mutant allele in cases of ALS is by using allele-specific small interfering RNAs (siRNAs), an approach that has been already described in several autosomal dominant diseases such as Parkinson’s disease,16 Alzheimer’s disease17 and Huntington’s disease.18,19 Silencing of a superoxide dismutase 1 (SOD1) mutant allele has been successfully achieved using siRNAs and short hairpin RNA in cells and animal models of ALS.20–22. The gene discussed is SOD1; the disease is Parkinson disease.