CIITA and MHC class II deficiency: The transcriptional regulation of the CIITA gene (also referred to as C2TA or MHC2TA) on chromosome 16p13, and the impact of genetic variation involving this gene for disease, has been extensively characterised following the identification of rare loss-of-function mutations in CIITA resulting in the bare lymphocyte syndrome and severe immunodeficiency due to lack of expression of Major Histocompatibility Complex (MHC) class II genes [1].