CALR mutant protein rescues the response of MPL p.R464G variant associated with CAMT to eltrombopag.

Abstract

Congenital amegakaryocytic thrombocytopenia (CAMT) is a severe inherited thrombocytopenia due to loss-of-function mutations affecting the thrombopoietin (TPO) receptor, MPL. Here, we report a new homozygous MPL variant responsible for CAMT in one consanguineous family. The propositus and her sister presented with severe thrombocytopenia associated with mild anemia. NGS revealed the presence of a homozygous MPLR464G mutation resulting in a weak cell surface expression of the receptor in platelets. In cell lines, we observed a defect in MPLR464G maturation associated to its retention in the endoplasmic reticulum. The low cell surface expression of MPLR464G induced very limited signaling with T..