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目的探讨1例FAS基因突变导致ALPS的临床特征、基因变异及其蛋白表达水平。方法患儿为男性,婴幼儿期起病,慢性、非恶性淋巴结和肝脾肿大,伴自身免疫性溶血性贫血、血小板减少及粒细胞减少。采用流式细胞仪检测双阴性T淋巴细胞和FAS蛋白表达。采用PCR方法扩增患儿及父母FAS基因组DNA。采用RT-PCR扩增患儿及父母FAS mRNA。PCR产物直接进行双向序列测定及FAS突变基因表达频率测定。结果患儿CD3+CD4-CD8-TCRαβ+T细胞12.68%,T淋巴细胞上FAS蛋白的表达为9.96%,较正常对照降低。基因检测为患儿FAS基因4号外显子93位碱基错义突变(T>A),导致FAS蛋白第143位氨基酸由丝氨酸替换为半胱氨酸(Ser14Cys),其父为携带者。患儿FAS基因突变基因表达频率为95%,其父为60%。结论经临床、免疫学筛查和基因分析,患儿可诊为ALPS(g:18451T>A c:773T>A Ser143Cys),突变基因表达的频率可能影响疾病外显率。
Objective To investigate the clinical features, gene mutation and protein expression of ALPS in a case of FAS gene mutation. Methods The children were male, infants and young children onset, chronic, non-malignant lymph nodes and hepatosplenomegaly, with autoimmune hemolytic anemia, thrombocytopenia and neutropenia. Double-negative T lymphocytes and FAS protein expression were detected by flow cytometry. PCR method was used to amplify FAS genomic DNA in children and their parents. FAS mRNA was amplified by RT-PCR from children and parents. PCR products were directly bi-directional sequencing and FAS mutation gene expression frequency determination. Results The expression of FAS protein was 12.68% in CD3 + CD4-CD8-TCRαβ + T cells and 9.96% in T lymphocytes, which was lower than that in normal controls. The gene was detected as a base missense mutation at exon 4 of FAS gene in children (T> A), resulting in the substitution of Serine to Ser14Cys at amino acid position 143 of FAS protein. Children with FAS gene mutation frequency of 95%, the father was 60%. Conclusion The clinical manifestations of ALPS (g: 18451T> A c: 773T> A Ser143Cys) can be diagnosed in children by clinical screening, immunological screening and gene analysis. The frequency of mutant gene expression may affect the disease penetrance.