IMD24 is an autosomal recessive immunodeficiency characterized by the impaired capacity of activated T and B cells to proliferate in response to antigen receptor-mediated activation. Patients have early onset of severe chronic viral infections, mostly caused by herpesviruses, including Epstein-Barr virus (EBV) and varicella zoster virus (VZV); they also suffer from recurrent encapsulated bacterial infections, a spectrum typical of a combined deficiency of adaptive immunity (CID) (summary by Martin et al., 2014).