PID01, the previously diagnosed MSMD patient with a mutation in IFNGR1 (c.818del4), showed very high levels of IFN-γR1 expression but contrastingly had very low levels of IFN-γ signalling (pSTAT1 fold change) through the receptor as well as reduced IL-12 production upon IFN-γ stimulation. The gene discussed is IFNG; the disease is Mendelian susceptibility to mycobacterial diseases.