OBJECTIVEInterleukin-12 receptor beta1 (IL-12 Rbeta1) deficiency is a rare primary immunodeficiency (PID) characterized by selective susceptibility to weakly virulent organisms, including Mycobacterium bovis, BCG, non-tuberculous environmental mycobacteria and non-typhoidal salmonellosis. The present study was conducted to identify the mutation type and to analyze clinical phenotype.

METHODSBased on the typical clinical manifestations and immunologic tests in this case, a varieties of PIDs were excluded and IL-12Rbeta1 deficiency was suspected. IL-12Rbeta1 chain expressed on Epstein-Barr virus-transformed lymphoblastoid B cell lines were detected by flow cytometric assay. The IL-12Rbeta1 gene sequences of the patient and her parents were analyzed by PCR-directed sequencing. The IL-12Rbeta1 gene sequences of the patient's younger brother also had been analyzed prenatally and after birth.

RESULTSAfter inoculating BCG, the patient suffered from multiple BCG infectious lymphadenitis. There was no detectable IL-12Rbeta1 on the Epstein-Barr virus-transformed lymphoblastoid B cell lines from the patient, while only mild expression on the cell line from her mother. Sequencing analysis by using sense and antisense primers separately, a novel IL-12Rbeta1 gene mutation was found in the patient which was homozygous single nucleotide substitution, a nonsense mutation with nucleotide substitution of C to T at position 853 (853C-->T) in exon 9 leading the glutamate at position 285 to the stop codon mutation (Q285X). The parents were carriers of the mutated IL-12Rbeta1 gene. But her younger brother has normal IL-12Rbeta1 gene.

CONCLUSIONThe novel IL-12Rbeta1 gene mutation is responsible for BCG infection in this case and genetic analysis is useful in carrier detection and prenatal diagnosis is feasible when the mother had a baby with identified IL-12Rbeta1 gene mutation before.