FAS基因突变导致自身免疫性淋巴细胞增生综合征(ALPS)一例

Characterization of a novel missense mutation in fas gene in a patient with autoimmune lymphoproliferative syndrome

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。

Here we reported the molecular and clinical characterization of a patient with autoimmune lymphoproliferative syndrome（ALPS） caused by a novel missense mutation in fas gene.A male patient and his healthy parents were enrolled in this study.Since childhood,the patient had chronic,non-malignant lymph nodes and hepatosplenomegaly,with autoimmune hemolytic anemia,thrombocytopenia and neutropenia.He was initially diagnosed of autoimmune lymphoproliferative syndrome according to clinical manifestations and immunological analysis.Flow cytometry was used to determine CD3＋CD4-CD8-TCRαβ＋ T cells and FAS expression on T cells.Fas gene of the patient and his parents were amplified by polymerase chain reaction（PCR） from genomic DNA.Reverse transcription polymerase chain reaction（RT-PCR） was used to amplify the fas transcripts.Sequencing analysis was performed directly on the PCR products in forward and reversely.At the same time,mutation frequency of FAS gene expression was determined.Results showed there were increased percentage of CD3＋CD4-CD8-TCRαβ＋T cells（12.68%） and induced percentage of FAS expression on T cells（9.96%） in the peripheral blood.The patient showed a genetic variation in exon 4 of fas gene,which resulted in a Ser143Cys amino acid substitution.The patient＇s father was identified as a carrier for this mutation.The expressed frequency of mutated FAS gene in the patient was 95%,whereas the father was 60%.In conclusion,a novel missense mutation of FAS which causes ALPS phenotype was identified in a Chinese child according immunologic screening and gene Sequencing.The expressed frequency of mutant gene may determine the penetrance.