De novo mutations involving the C-terminal tail of CDC42 cause distinct dyshematopoietic and autoinflammatory disorders

Pathogenic missense variants in CDC42 differentially affect protein function, causing a clinically wide phenotypic spectrum variably affecting neurodevelopment, hematopoiesis and immune response. More recently, three variants at the C-terminus of CDC42 were proposed to similarly impact protein function and cause a novel autoinflammatory disorder. We sought to clinically and functionally classify these variants to improve patient management. Comparative analysis of the available clinical data and medical history of patients was performed. In vitro and in vivo studies were carried out to functionally characterize individual variants. Differently from what had previously been observed for the p.R186C change causing NOCARH (Neonatal-Onset Cytopenia, Autoinflammation and Recurrent Hemophagocytic lymphohistiocytosis [HLH]), p.C188Y and p.*192Cext*24 promoted accelerated protein degradation. Unprenylated CDC42C188Y did not behave as a membrane-bound protein, while the residual CDC42*192Cext*24 mutant replicated the CDC42R186C behavior, being targeted to the Golgi apparatus in a palmitoylation-dependent manner. Assessment of in vitro polarized migration and development in C. elegans documented a loss-of-function behavior of the p.C188Y and p.*192Cext*24 variants. Consistently, the three pathogenic variants were associated with different clinical presentations, with dysmorphisms, severity and age of onset of cytopenia and extent of autoinflammation representing major differences. Pathogenic variants at the CDC42 C-terminus differently impact protein stability, localization and function, and cause different diseases, with p.R186C specifically associated with neonatal-onset pancytopenia and severe autoinflammation/HLH requiring emapalumab and bone marrow transplantation, and p.C188Y and p.*192Cext*24 causing anakinra-sensitive autoinflammation.