CTLA4 and type 1 diabetes mellitus: They have also prompted us to ask how genetic anomalies or variations in Treg development and function render the host susceptible not only to monogenic autoimmune diseases due to mutations of FOXP3, IL2RA, CTLA4 and other genes affecting Treg cell function, but also to various polygenic common autoimmune diseases (such as type 1 diabetes and rheumatoid arthritis), which afflict ~10% of the population worldwide.8