MFN2 and bile duct papillary neoplasm: IPNs have traditionally been considered Mendelian disorders, with the bulk of disease gene discovery and diagnostics focused on monogenic disease.2, 46 However, suspected digenic inheritance for IPN has been reported.19 21 Several reports have involved variants in MFN2 and GDAP1, where the cumulative effect of these variants has resulted in severe IPN.86, 89 Cassereau et al86 reported a patient with severe CMT harbouring previously observed pathogenic homozygous loss-of-function GDAP1 and heterozygous missense MFN2 variants.