MSN and immunodeficiency disease: Moesin is a cytoskeletal adaptor protein that belongs to the Ezrin-Radixin-Moesin (ERM) family of proteins which connects the actin cytoskeleton to the plasma membrane, regulating the structure and function of specific domains of the cell cortex.1,2 Moesin plays a pertinent role in immunity, acting on T and B-cell homeostasis and self-tolerance.3,4 As such, specific mutations in this ERM protein have implications in immunodeficiency.5,6 Studies have demonstrated that Moesin overexpression is associated with various cancer-related processes and can act as a prognostic marker.7–11