It has been reported that Mfn2 but not Mfn1 independently regulates not only MAM, but also mitophagy, obesity, cardiomyopathies, and several neuronal defects such as Charcot-Marie-Tooth disease, and Parkinson’s disease, suggesting that Mfn2 might not functionally compensate for Mfn1 (Chen and Dorn, 2013; Filadi et al., 2018; Sebastián et al., 2016). The gene discussed is MFN1; the disease is obesity due to melanocortin 4 receptor deficiency.