SOD1 and amyotrophic lateral sclerosis: The definition of a MAF threshold for ALS, in which significant confounding factors coexist (late-onset of the disease, age-dependent, variant-related reduced penetrance, and oligogenic inheritance), cannot ignore many factors difficult to evaluate, such as the inheritance model (monoallelic for most SOD1-ALS variants), the prevalence of the disease, and the penetrance.