MFN2 and Charcot-Marie-Tooth disease type 2A1: Only two human diseases are unambiguously attributed to functional MFN deficiency: Charcot-Marie-Tooth disease type 2A (CMT2A) that is almost always mono-allelic (i.e., heterozygous) with autosomal dominant inheritance (vide infra), and multiple symmetric lipomatosis that has been described with bi-allelic (i.e., homozygous or compound-heterozygous) MFN2 mutations (Rocha et al., 2017; Capel et al., 2018).