Although the loss of either Mfn1 or Mfn2 causes lethality in mice due to overtly fragmented mitochondria, mutations in human Mfn2 but not Mfn1 lead to Charcot-Marie-Tooth disease type 2A (CMT2A), peripheral neuropathy of long motor and sensory neurons (Züchner et al., 2004). Here, MFN1 is linked to Charcot-Marie-Tooth disease type 2A1.