X-连锁严重联合免疫缺陷病家系分析并文献复习

目的 总结分析严重联合免疫缺陷病（SCID）的临床表现、诊断方法和治疗。方法 对1例生后2个月内起病，严重感染，使用抗生素治疗效果不佳，生后5个月病死，常规实验室检查外周血淋巴细胞绝对计数减少,WBC总数2.8×109?L-1，L 1.9×109?L-1的患儿，使用流式细胞仪检测患儿及其双亲的外周血淋巴细胞表达，并抽提出DNA，对IL-2受体γ链（IL2RG）进行基因分析。外周血淋巴细胞转化试验检测患儿舅舅淋巴细胞增殖能力。回顾分析患儿家族史，通过问诊进行初步家系调查。结果 流式细胞仪检测患儿外周血CD3＋T细胞为0；NK细胞（CD16+CD56+）为4％。患儿X染色体q13.1的IL2RG基因的第6个外显子存在突变，突变位为849位碱基G缺失导致阅读框架移位，氨基酸序列位于278半胱氨酸处，并在293位产生“TGA”的终止密码子。患儿母亲被证实为携带者，但不是单纯的杂合子，可能存在嵌合突变。患儿被诊断为X-连锁严重联合免疫缺陷病（X-SCID）。患儿的舅舅生后因严重感染治疗无效而病死，其淋巴细胞转化试验植物血凝素（PHA）刺激72 h，外周血单个核细胞无增殖反应（CPM值为0）。病程中使用未经特殊处理的血制品后出现高热、皮疹和肝、脾肿大后病死。回顾分析家族史，患儿母系中近3代出生男性4例均因严重感染而在婴幼儿期夭折，考虑可能也是X-SCID，女性均健康。患儿妹妹经基因分析证实亦为携带者，为IL2RG基因的第6个外显子849位碱基嵌合型。患儿的舅舅使用未经特殊处理的血制品出现的临床表现为移植物抗宿主病可能。结论 经基因分析确诊了1例X-SCID，通过初步家系调查，基因分析证实患儿母亲及妹妹均为嵌合型携带者。临床上对出生后6个月内严重感染，治疗效果不佳者应警惕SCID的可能，并应进行免疫功能评价。如果疑为SCID患儿则不能接种活疫苗和使用未经特殊处理的血制品。早期的骨髓或干细胞移植可以重建患儿的免疫系统，提高长期生存率。应提高儿科医务人员对该病的认识。

A report of two cases of severe X-linked combined immunodeficiency in one family and literature review

Objective To investigate the clinical manifestations，diagnostic methods and treatment of severe combined immunodeficiency (SCID) . Methods The patient presented at the age of 2 months with frequent pneumonia and a history of chronic oral candidiasis even when treated adequately with antibiotics or anti fungi agents. Flow cytometric analysis was used to assess T cells. Cell surface markers of peripheral blood cells were determined by immunofluorescent staining and flow cytometry with antibodies purchased from BD company. IL 2R gene was analyzed by PCR and sequence was performed for the patient and partial maternal family members. Clinical documented information of the patient and his uncle died during early life was reviewed. His peripheral blood mononuclear cells were incubated at 37 ℃ in complete culture medium RPMI-1640. Cells were incubated in round bottom tissue culture plates with PHA for 72 h, and 18-20 hours before termination of the culture, thymidine was added to each well. The cells were then harvested and samples were counted in a liquid scintillation counter. Results The patient had a very low T cell number. Initial investigations revealed a total white blood cell count of 2.8×109?L-1［reference range, (5.4-9.4)×109?-1］ with a lymphocyte count of 1.9×109?L-1［reference range, （2.8-5.7）×109?L-1］, the results of flow cytometric analysis showed CD3+ 0, CD4+ 0, CD8+ 0, CD19+ 95%, CD16+CD56+ 4%. Sequencing of his IL-2RG revealed a G deletion at 849 in exon 6, the consequence showed frameshift start form cysteine 278, “TGA” stop codon created at position 293. His mother was confirmed to be a carrier, she didn't seem to be a simple heterozygote,but maybe mosaic mutation with mixed population in leucocytes. His uncle died of severe incurable infection and without mononuclear proliferation to PHA stimulation. He presented hyperpyrexia, rash and splenohepatomegalia after recieving transfusion of untreated fresh blood. Considering his family history, his uncle's clinical manifestation was high likely due to graft versus host disease. IL2R gene analysis was also done for his newborn sister after family survey.His sister was confirmed to be the same mutation as her mother. Conclusions Genetic diagnosis was made for one X-SCID patient caused by IL-2RG. And after family survey, his mother and sister were confirmed to be carriers, maybe mosaic mutation with mixed population in leucocytes. Infant with severe infection even after treated with adequate standard treatment, should be considered the possibility of suffering SCID and immune function evaluation should be taken. As the underlying severe disorders, the living vaccine and untreated blood products transfusion must be restrained. Early immune reconstitution including bone marrow or stem cell transplantation offers the best chance of long-term survival. Medical workers should pay more attention to immunodeficiency.