In principle, this approach could be applied to other haploinsufficiency disorders, including monogenetic diabetes (MODY) and neurofibromatosis type 1, or to upregulate homozygous mutants where the mutant protein retains some function, as was recently shown for cystic fibrosis transmembrane conductance regulator (CFTR).47 Here, CFTR is linked to neurofibromatosis type 1.