While it is reasonable to hypothesize that our heterozygous HK1-CHI and CACNA1D patients had changes reminiscent of Sempoux’ morphological mosaicism of islets throughout the entire pancreas, it is not possible to determine whether the genetically mosaic HK1-CHI patients had widespread or localized changes without cure after 50-80% pancreatic resection. Here, HK1 is linked to congenital isolated hyperinsulinism.