Schematic presentation of SGR in conditions caused by autosomal dominant haploinsufficient genetic variants. Four causative mechanisms for these conditions have been described (Rescue events), either by making use of the functional wild-type allele (reversion by mitotic recombination resulting in segmental UPD, or promoter activation) or by correcting functionality of the mutated copy through a compensating mutation or a back mutation. A compensating mutation (blue dot) occurs on a different location within the same gene copy and takes away the deleterious effect of the pathogenic mutation (green dot), for example, by restoring the reading frame of a pathogenic frameshift mutation. A back mutation reverts the original mutation back to normal. The GATA2 rescue event described by Catto and coworkers is of the “back mutation” type, where in the pathogenic germline GATA2 c.216C>A (p.Y72*) variant, the A residue is spontaneously remutated into a T, by which the amino acid sequence is restored (c.216C>T; p.Y72Y).