HFE and amyotrophic lateral sclerosis: However, the sample size was small (22 ALS patients with wild-type HFE and 16 ALS patients either homozygous or heterozygous for the p.H63D HFE polymorphism) and a selection bias was contemplated by the authors, since many of the patients selected for muscle biopsy underwent this procedure because their clinical and/or electrodiagnostic findings were in some way atypical.