Allelic heterogeneity of Proteus syndrome

Proteus syndrome is a mosaic disorder that can cause progressive postnatal overgrowth of nearly any organ or tissue. To date, Proteus syndrome has been exclusively associated with the mosaic c.49G > A p.(Glu17Lys) pathogenic variant in AKT1, a variant that is also present in many cancers. Here we describe an individual with severe Proteus syndrome who died at 7.5 yr of age from combined parenchymal and restrictive pulmonary disease. Remarkably, this individual was found to harbor a mosaic c.49_50delinsAG p.(Glu17Arg) variant in AKT1 at a variant allele fraction that ranged from AKT1.