Objective       To explore the clinical features

detect the function of the IL-12/23-IFN-γ axis and identify the IFN-γ receptor 1 (IFNGR1) gene mutation in a child with suspected Mendelian susceptibility to mycobacterial disease (MSMD).        Methods       Firstly

we ruled out the common primary immunodeficiency disease (PID) based on the clinical manifestation and screening tests of immune function

and then detected the integrity of the IL-12/23-IFN-γ axis by Q-RT-PCR. IFNGR1 gene was sequenced according to the results of Q-RT-PCR.        Results       The child suffered from disseminated BCG disease and multi-system lesions. The production of IL-12B in response to BCG plus IFN-γ was reduced

compared with stimulation by BCG alone (P0.05). A heterozygous deletion mutation was found at the position of 818 to 821 (c.818-821 del TTAA) in exon 6 of IFNGR1 gene that resulted in proline at the position of 276 changing into the stop codon (p.Asn274fsX276) in the patient. In contrast

IFNGR1 genes were normal in her parents.        Conclusion       MSMD Chidren have the clinical feature of disseminated BCG disease and multi-system lesions. Detecting the function of IL-12/23-IFN-γ axis is an effective tool for the screening of MSMD. IFNGR1 genetic mutation is responsible for BCG infections and multi-system lesions in this child.