Wang Xiao-chuan, Wang Ying, Kanegane Hirokazu, Toshio Miyawaki, Yu Ye-heng
Department of Clinical Immunology, Children's Hospital, Fudan University, Shanghai 200032, China.
Zhonghua Er Ke Za Zhi. 2005 Jun;43(6):449-52.
X-linked agammaglobulinemia (XLA) is the most common disorder among primary immunodeficiency diseases, which is caused by mutations in the cytoplasmic Bruton's tyrosine kinase (BTK) gene, characterized by lack of mature, circulating B lymphocytes, hypogammaglobulinemia, and recurrent bacterial infections. Mutations in BTK are highly diverse. In this study, genetic analysis was performed on BTK to realize the feature of gene mutation of XLA in Mainland of China.
Seven patients from 7 different families were enrolled in the analysis. RT-PCR was employed to reverse transcript total RNA and 8 couples of primers were designed for PCR. PCR products were sequenced and the mutation sites were identified.
Seven completely different mutations were identified in the 7 patients. All the 7 mutations located at BTK coding region. Three of the 7 mutations were located in pleckstrin homology functional area, 2 mutations located in BTK area, and in other 2 cases at Src homology 2 and Src homology 3 regions, respectively. The mutations in 2 of 7 cases were in exon 18, and the others were in exon 2, 5, 6, 8 and 10, respectively. The types of mutation included 3 missense (L11P, I590F and Y591S), two nonsense (W281X, and Q234X) mutations resulting in premature stop codons. A 10-base pair nucleotides duplicated insertion located between the nucleotide 596 and 597 resulting in frameshift, and a 8 base pair deletion at the nucleotide position 472 resulting in frameshift. Four of the 7 mutations are novel mutation types and have not been reported. Four of 7 mothers were analyzed, 3 of them were carrier and 1 was normal.
The patients enrolled in this study had classical clinical features of XLA. All the 7 identified mutations located at BTK coding region and 4 of them were novel mutations. Genetic analysis can be used for diagnosis of XLA and distinguish it from other hypogammaglobulinemia.
X连锁无丙种球蛋白血症（XLA）是原发性免疫缺陷病中最常见的疾病，由细胞质布鲁顿酪氨酸激酶（BTK）基因突变引起，其特征为缺乏成熟的循环B淋巴细胞、低丙种球蛋白血症和反复细菌感染。BTK基因突变具有高度多样性。本研究对BTK进行基因分析，以了解中国内地XLA基因突变特征。
纳入7个不同家庭的7例患者进行分析。采用RT-PCR反转录总RNA，并设计8对引物用于PCR。对PCR产物进行测序并鉴定突变位点。
7例患者共鉴定出7种完全不同的突变。所有7种突变均位于BTK编码区。7种突变中有3种位于普列克底物蛋白同源功能区，2种位于BTK区，另外2种分别位于Src同源2区和Src同源3区。7例中有2例的突变位于外显子18，其余分别位于外显子2、5、6、8和10。突变类型包括3种错义突变（L11P、I590F和Y591S）、2种无义突变（W281X和Q234X）导致提前终止密码子。在核苷酸596和597之间有一个10个碱基对的核苷酸重复插入导致移码，在核苷酸位置472有一个8个碱基对缺失导致移码。7种突变中有4种是新的突变类型，尚未见报道。对7例患者的母亲中的4例进行分析，其中3例为携带者，1例正常。
本研究纳入的患者具有XLA的典型临床特征。鉴定出的7种突变均位于BTK编码区，其中4种为新突变。基因分析可用于XLA的诊断，并将其与其他低丙种球蛋白血症相鉴别。
