SMN1 and amyotrophic lateral sclerosis: Other common genetic risk factors that increase the probability of ALS occurrence are an intermediate expansion of the CAG trinucleotide repeat in the ataxin-2 (ATXN2) gene, variants in elongator complex protein 3 (ELP3), survival motor neuron protein (SMN1) copy number variation, and insertion or deletion mutations in the neurofilament heavy polypeptide (NEFH) gene [131].