原发性免疫缺陷病合并卡介苗感染新型白介素12受体β1基因突变一例

Primary immunodeficiency complicated with Bacillus Calmette-Guerin infection： identification and clinical phenotype of a case of novel interleukin-12Rβ1 gene mutation

目的分析一例白介素12受体β1（IL-12Rβ1）缺陷基因突变合并卡介苗感染患儿的临床特征、基因分析和蛋白表达。方法根据典型的临床表现及免疫学筛查实验排除常见原发性免疫缺陷病（PID），用单克隆抗体流式细胞术检测患者和母亲EB病毒（EBV）永生化的B细胞上IL-12Rβ1蛋白表达，同时，用正向、反向引物分别对患儿和其父、母的IL-12Rβ1基因进行PCR扩增并测序，患儿弟弟产前、产后均已作IL-12Rβ1基因分析。结果患儿有严重、播散性卡介苗接种病，其永生化的B细胞上IL-12Rβ1蛋白表达呈阴性，母亲有部分蛋白表达。患儿为IL-12Rβ1基因纯合单核苷酸替换突变，其第9外显子853位核苷酸（C→T）发生无义突变，使第285位谷氨酸突变为终止密码（Q285X），其父、母亲均为该异常基因的携带者，患儿弟弟产前产后IL-12Rβ1基因正常。结论鉴定出一例新型IL-12Rβ1基因突变（Q285X）患者，发现此基因突变患者的IL-12Rβ1蛋白缺乏，确定此基因突变是引起患者发生播散性卡介苗接种病的根本原因；明确家庭成员携带情况，为产前诊断提供依据。

Objective Interleukin-12 receptor β1 （IL-12 Rβ1 ） deficiency is a rare primary immunodeficiency （PID） characterized by selective susceptibility to weakly virulent organisms, including Mycobacterium boris, BCG, non-tuberculous environmental mycobacteria and non-typhoidal salmonellosis. The present study was conducted to identify the mutation type and to analyze clinical phenotype. Methods Based on the typical clinical manifestations and immunologic tests in this case, a varieties of PIDs were excluded and IL-12Rβ1 deficiency was suspected. IL-12Rβ1 chain expressed on Epstein-Barr virus- transformed lymphoblastoid B cell lines were detected by flow cytometric assay. The IL-12Rβ1 gene sequences of the patient and her parents were analyzed by PCR-directed sequencing. The IL-12Rβ1 gene sequences of the patient＇s younger brother also had been analyzed prenatally and after birth. Results After inoculating BCG, the patient suffered from multiple BCG infectious lymphadenitis. There was no detectable IL-12Rβ1 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-12Rβ1 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-12Rβ1 gene. But her younger brother has normal IL-12Rβ1 gene. Conclusion The novel IL- 12Rβ1 gene mutation is responsible for BCG infection in this case and genetic analysis is useful in cartier detection and prenatal diagnosis is feasible when the mother had a baby with identified IL-12Rβ1 gene mutation before. I