Clinical features and mutation analysis of X-linked agammaglobulinemia in 20 Chinese patients

Background

X-linked agammagobulinemia (XLA) is a primary immunodeficiency caused by Bruton’s tyrosine kinase (BTK) gene mutation. XLA patients have an extremely small amount of peripheral B cells and profound deficiency in all immunoglobulin isotypes. We analyzed the clinical, immunologic, and molecular characteristics of children with XLA in an attempt to improve the diagnosis and treatment of XLA in China.

Methods

Twenty children with XLA-compatible phenotypes from 18 unrelated families were enrolled in this study. The BTK gene was amplified and sequenced, followed by mutation analysis in these children and their female relatives.

Results

Eighteen different mutations of the BTK gene were identified in the 20 patients. Eleven mutations had been reported previously including eight missense mutations (c.994C>T, c.1987C>A, c.1885G>T, c.502T>C, c.1085C>T, c.1816C>T, c.214C>T, c.1912G>A) and three nonsense mutations (c.1267T>A, c.1793C>G, c.1618C>T). Seven novel mutations of the BTK gene were also presented and included five missense mutations (c.134T>A, c.1646T>A, c.1829C>G, c.711G>T, c.1235G>A), one splice-site mutation (c.523+1G>A) and one insertion mutation (c.1024-1025in sTTGCTAAAGCAACTGCTAAAGCAAG). Eight out of 18 mutations of the BTK gene were located in the TK domain, 4 in the PH domain, 4 in the SH2 domain and 2 in the TH domain. Genetic study for carrier status was carried out in 18 families with definite BTK gene mutations. Nine carriers with BTK gene mutations were identified. Six families without carriers were detected, and 3 patients were not tested in this study.

Conclusion

Our results support that molecular genetic testing represents an important tool for early confirmed diagnosis of congenital agammaglobulinemia and may allow accurate carrier detection and prenatal diagnosis.     

Novel BTK mutation presenting with vaccine-associated paralytic poliomyelitis

Oral polio vaccine (OPV) has been used safely and efficiently for more than 40 years in preventive medicine. Vaccine-associated paralytic poliomyelitis (VAPP) is a rare adverse event of OPV due to reversion of the vaccine strain virus to a neurovirulent strain. VAPP can occur in healthy recipients or their close contacts. However, persons with primary humoral immunodeficiencies are at a much higher risk. X-linked agammaglobulinemia (XLA) is a prototypic humoral deficiency caused by mutations in the Bruton’s tyrosine kinase (BTK) gene. In addition to susceptibility to bacterial infections, patients with XLA are especially prone to enteroviruses. Here, we describe the occurrence of VAPP in a 15-month old Iranian boy. The child had received four doses of OPV, administered at birth, 2, 4, and 6 months of age. The patient’s infectious history was unremarkable. Laboratory evaluation revealed low levels of immunoglobulin G and CD19⁺ B cells of less than 1% of the lymphocyte population. A novel insertion (c.685_686insTTAC) in the SH3 domain of the BTK gene was detected as the underlying cause. Immunodeficient recipients of OPV can excrete poliovirus vaccine strains for a long period and are at risk of developing flaccid paralysis. They could also serve as a source of reverted virulent poliovirus to be reintroduced into the general population. This patient presented for the first time with VAPP, without any history of other major infections in 15 months. This suggests that a negative history for recurrent infections does not exclude the presence of a primary defect in the immune system.     

Comprehensive molecular analysis of Japanese patients with pediatric-onset MODY-type diabetes mellitus

Yorifuji T, Fujimaru R, Hosokawa Y, Tamagawa N, Shiozaki M, Aizu K, Jinno K, Maruo Y, Nagasaka H, Tajima T, Kobayashi K, Urakami T. Comprehensive molecular analysis of Japanese patients with pediatric‐onset MODY‐type diabetes mellitus. Background: In Asians, mutations in the known maturity‐onset diabetes of the young (MODY) genes have been identified in only <15% of patients. These results were obtained mostly through studies on adult patients. Objective: To investigate the molecular basis of Japanese patients with pediatric‐onset MODY‐type diabetes. Subjects: Eighty Japanese patients with pediatric‐onset MODY‐type diabetes. Methods: Mitochondrial 3243A>G mutation was first tested by the polymerase chain reaction restriction fragment length polymorphism analysis for maternally inherited families. Then, all coding exons and exon–intron boundaries of the HNF1A, HNF1B, GCK, and HNF4A genes were amplified from genomic DNA and directly sequenced. Multiplex ligation‐dependent probe amplification analysis was also performed to detect whole‐exon deletions. Results: After excluding one patient with a mitochondrial 3243A>G, mutations were identified in 38 (48.1%) patients; 18 had GCK mutations, 11 had HNF1A mutations, 3 had HNF4A mutations, and 6 had HNF1B mutations. In patients aged <8 yr, mutations were detected mostly in GCK at a higher frequency (63.6%). In patients >9 yr of age, mutations were identified less frequently (45.1%), with HNF1A mutations being the most frequent. A large fraction of mutation‐negative patients showed elevated homeostasis model assessment (HOMA) insulin‐resistance and normal HOMA‐β indices. Most of the HNF1B mutations were large deletions, and, interestingly, renal cysts were undetectable in two patients with whole‐gene deletion of HNF1B. Conclusion: In Japanese patients with pediatric‐onset MODY‐type diabetes, mutations in known genes were identified at a much higher frequency than previously reported for adult Asians. A fraction of mutation‐negative patients presented with insulin‐resistance and normal insulin‐secretory capacities resembling early‐onset type 2 diabetes.     

X连锁无丙种球蛋白血症的基因诊断

目的研究我国X连锁无丙种球蛋白血症(XLA)患者Bruton’s酪氨酸激酶(BTK)基因的突变类型。方法采用逆转录-聚合酶链反应(RT—PCR),获得7例XLA患者cDNA。使用8对不同引物分2步扩增BTK cDNA,PCR产物测序。突变结果通过对DNA外显子相应部位扩增、测序证实。对其中4例母亲进行基因分析。结果7例患者的基因突变均位于BTK基因的编码区,3例在BTK的血小板-白细胞C激酶底物同源区,2例位于酪氨酸激酶区,其他2例分别位于Src同源区2和Src同源区3。突变包括：错义突变、无义突变、重复序列和片段缺失。除错义突变引起单一BTK氨基酸改变外,突变还分别造成终止密码子形成和阅读框架移位。其中4例为未见报道的新突变。进行基因分析的4例母亲中,3例为携带者。结论本组患者临床表现为典型XLA,检测出的7种突变均位于BTK基因编码区,其中4种是未见报道的新突变。XLA可以通过基因分析进行确诊以区别与其他低丙种球蛋白血症。     

Association of ventricular septal defect with rare variations of the HAND2 gene北大核心CSCD

目的对室间隔缺损(ventricular septal defect,VSD)与HAND2基因启动子区罕见变异的关联性进行分析,并对相关分子机制进行初步探索。方法收集349例VSD组患儿和345例健康对照组儿童血液样本,通过聚合酶链反应扩增目的片段并进行测序,确定HAND2基因启动子区的罕见变异位点。使用双荧光素酶检测进行变异位点功能分析,并通过电泳迁移率变动分析进行分子机制研究,同时使用TRANSFAC和JASPAR数据库预测转录因子。结果通过测序发现3个变异位点(g.173530852A>G、g.173531173A>G和g.173531213C>G)只出现在10例VSD患儿的HAND2基因启动子上,其中4例患儿仅有1个变异位点。双荧光素酶检测显示g.173531213C>G降低了HAND2基因启动子转录活性。电泳迁移率变动分析和转录因子预测提示g.173531213C>G产生了1个转录因子结合位点。结论HAND2基因启动子区的罕见变异g.173531213C>G可能通过影响转录因子的结合,进而参与VSD的发生发展。     

Genotype-phenotype correlation in Bruton's tyrosine kinase deficiency

Bruton's tyrosine kinase (Btk) belongs to the Tec family of nonreceptor protein tyrosine kinases. Mutations in the BTK gene cause X-linked agammaglobulinemia (XLA); a primary immunodeficiency disorder in human. No clear genotype-phenotype correlation has been established in XLA so far. To determine how differently mutations in BTK affect the severity of the disease and if BTK promoter polymorphic variant or intron 1 polymorphic variant in Tec, a cytoplasmic tyrosine kinase that might substitute for Btk, could contribute to the clinical phenotype, we analyzed the clinical and molecular findings in a cohort of XLA patients. Polymorphisms in BTK promoter and TEC intron 1 regions include substitutions of C>T (rs2071219) and T>C (rs2664019), respectively. Btk expression was evaluated by means of western immunoblotting and fluorescence-activated cell sorter analysis. Mutations were categorized as mild or severe and patients were evaluated for the clinical severity of disease. On the basis of the results, severe genotypes do not necessarily lead to severe phenotypes. More over, in a considerable number of patients with mild phenotype we showed a severe mutation with a tendency toward C substitution in the polymorphic site on TEC intron 1.     

ZFPM2基因的低频变异通过影响GATA4转录调控参与圆锥动脉干畸形的发生

摘要 目的：通过Sanger测序,检测圆锥动脉干畸形（CTA）患儿中ZFPM2基因的突变情况,并探讨其致病性及相关分子机制。方法： 对复旦大学附属儿科医院收治的非综合征型CTA患儿的心肌组织标本cDNA进行Sanger测序,检测ZFPM2基因的突变情况。构建ZFPM2、GATA4的表达载体和ANF启动子载体,并将ZFPM2突变型引入表达载体。采用免疫共沉淀（Co-IP）结合Western blotting的方法研究野生型或突变型ZFPM2与GATA4的相互作用。采用荧光素酶报告基因系统研究野生型或突变型ZFPM2对ANF启动子活性的影响。通过mRNA注射研究hZFPM2突变对斑马鱼心脏表型的影响。结果：①对107例非综合征型CTA患儿进行Sanger测序,男64例,年龄1月至14岁（中位年龄8个月）;包括单纯型法洛四联症（TOF）39例,TOF合并卵圆孔未闭（PFO）29例,TOF合并房间隔缺损（ASD）6例,TOF合并PFO和动脉导管未闭（PDA）8例,25例为复杂表型［如房室间隔缺损（AVSD）和左位上腔静脉（LSVC）等］。②在1例TOF合并PFO的患儿中,发现位于ZFPM2基因外显子4的1个杂合错义变异c.397A>Gp.M133V（rs77117583）,它仅出现在东亚人群,突变频率为0.3‰,位于ZFPM2蛋白的N端转录抑制结构域,该结构域对于ZFPM2调控的GATA4依赖性转录是必需的。③HEK293T细胞和HL-1细胞中的Co-IP结果均表明ZFPM2发生M133V突变后与GATA4的结合增强。④荧光素酶报告基因实验：人胚肾细胞株HEK293T和小鼠心肌细胞株HL-1中的结果均表明,ZFPM2发生M133V突变后,其抑制GATA4对ANF的转录激活的作用增强。⑤mRNA注射斑马鱼胚胎后心脏发育畸形情况：未注射的对照组、WT组和M133V突变体组心脏畸形发生率分别为11.3%、15.0%和27.5%,M133V突变体组高于其他两组（P＜0.05）。心脏异常表现为：心脏的环化发生异常,心房和心室与正常心脏呈镜像。结论：在1例CTA患儿中检测到1个ZFPM2低频变异c.397A>G, p.M133V,它可能通过影响ZFPM2与GATA4的结合及GATA4转录调控来参与CTA的发生。     

Steroid 11-beta hydroxylase deficiency caused by compound heterozygosity for a novel mutation in intron 7 (IVS 7 DS+4A to G) in one CYP11B1 allele and R448H in exon 8 in the other

Congenital adrenal hyperplasia (CAH) due to steroid 11-beta hydroxylase deficiency (11β-OHD) is a rare genetic disorder of steroidogenesis transmitted as an autosomal recessive trait. We describe a new case of 11β-OHD CAH caused by compound heterozygosity for a novel mutation in intron 7 and previously described mutation in exon 8 of CYP 11B1 gene. A 2.5-year-old boy of Croatian descent presented with accelerated growth and bone age, borderline hypertension, and pseudoprecocious puberty. Hormonal studies established diagnosis of 11β-OHD: elevated plasma levels of 11-deoxycortisol, 17-hydroxyprogesterone, androstenedione and testosterone, low levels of cortisol and aldosterone, and suppressed plasma renin activity. Sequencing of the CYP11B1 gene identified compound heterozygous mutation consisting of a novel splicing mutation in intron 7 (IVS 7DS+4A to G) and R448H mutation in exon 8 previously reported mostly in Moroccan Jews. This is the first patient with CAH due to 11β-OHD in Croatia (and Slavic population in general) in whom molecular diagnosis of CYP11B1 gene was performed.     

Recent progress in the diagnosis and treatment of patients with defects in early B-cell development

Mutation detection for X-linked agammaglobulinemia (XLA) has revealed the heterogeneity of the clinical phenotype of patients with defects in Bruton's tyrosine kinase (Btk), the gene that is abnormal in XLA. Over 50% of patients with mutations in Btk have no family history of the disease because their cases are the first manifestation of a new mutation in their family. In 10% to 20% of patients, the serum immunoglobulins are higher than expected or the onset of disease is delayed; however, a marked reduction in B-cell numbers is consistent in all patients. Mutation detection has also shown that not all patients with presumed XLA have mutations in Btk. Mutations in mu heavy chain, and other components of the pre-B cell receptor complex, including lambda 5/14.1, cause a disorder that is clinically identical to XLA. Although new strategies for therapy are not yet available, the groundwork is being laid for cell or gene therapy.     

Mutation screening of the BTK gene in 56 families with X-linked agammaglobulinemia (XLA): 47 unique mutations without correlation to clinical course

OBJECTIVES: To determine the utility of single-stranded conformation polymorphism (SSCP) analysis for mutation screening in the BTK (Bruton's tyrosine kinase) gene, we investigated 56 X-linked agammaglobulinemia (XLA) families. To obtain genotype/ phenotype correlations, predicted protein aberrations were correlated with the clinical course of the disease. PATIENTS: This study included 56 patients with XLA, with or without a positive family history, who were diagnosed on the basis of their clinical features, low peripheral B-cell count, and low immunoglobulin levels. Ten patients with isolated hypogammaglobulinemia and 50 healthy males served as controls. METHODS: SSCP analysis was performed for the entire BTK gene, including the exon-intron boundaries and the promoter region. Structural implications of the missense mutations were investigated by molecular modeling, and the functional consequences of some mutations also were evaluated by in vitro kinase assays and Western blot analysis. RESULTS: We report the largest series of patients with XLA to date. All but 5 of the 56 index patients with XLA screened with SSCP analysis showed BTK gene abnormalities, and in 2 of the 5 SSCP-negative patients, no BTK protein was found by Western blot analysis. There were 51 mutations, including 37 novel ones, distributed across the entire gene. This report contains the first promoter mutation as well as 14 novel missense mutations with the first ones described for the Tec homology domain and the glycine-rich motif in the SH1 domain. Each index patient had a different mutation, except for four mutations, each in two unrelated individuals. This result supports the strong tendency for private mutations in this disease. No mutations were found in the controls. CONCLUSIONS: Our results demonstrate that molecular genetic testing by SSCP analysis provides an accurate tool for the definitive diagnosis of XLA and the discrimination of borderline cases, such as certain hypogammaglobulinemia or common variable immunodeficiency patients with overlapping clinical features. Genotype/ phenotype correlations are not currently possible, making prediction of the clinical course based on molecular genetic data infeasible.     

5042例地中海贫血高风险儿童β-地中海贫血基因分析

目的了解广州地区地中海贫血(地贫)高风险儿童β-地贫的检出率及基因型构成情况,为制定广州地区β-地贫防治策略、有效降低β-地贫的发病率提供参考。方法应用双重PCR结合反向斑点杂交技术(reverse dot blot,RDB),对广州地区的5042例地贫高风险患儿进行β-地贫8种常见和9种稀少的突变位点进行基冈分析。结果在5042例受检者中,共检出β-地贫患儿1507例,约为受检者的29.89%,涉及13种突变类型。其中CDs41-42(-TCTT)、IVS-Ⅱ-654(C→T)、CD17(A→T)、-28(A→G)、CD71-72(+A)、CD26(G→A)、CD43(G→T)是广州地区最主要的7种β-地贫基因突变类型,分别占42.09%、26.01%、12.63%、10.42%、2.97%、2%、1.02%,这7种突变占全部检出突变的97.14%。纯合子109例(7.23%),双重杂合子237例(15.73%)。结论广州地区地贫高风险患儿具有较高的β-地贫突变基因检出率,制定切实有效的地贫防治策略对于减少β-地贫纯合子和双重杂合子的出生率,提高广州地区的人口素质十分重要。     

First 2 cases with thiamine‐responsive megaloblastic anemia in the Czech Republic,a rare form of monogenic diabetes mellitus: a novel mutation in the thiamine transporter SLC19A2 gene—intron 1 mutation c.204+2T>G

Thiamine‐responsive megaloblastic anemia (TRMA) is a rare autosomal recessive disorder caused by mutations in the SLC19A2 gene. To date at least 43 mutations have been reported for the gene encoding a plasma membrane thiamine transporter protein (THTR‐1). TRMA has been reported in less than 80 cases worldwide. Here, we illustrate 2 female patients with TRMA first diagnosed in the Czech Republic and in central Europe being confirmed by sequencing of the THTR‐1 gene SLC19A2. Both subjects are compound heterozygotes with 3 different mutations in the SLC19A2 gene. In case 2, the SLC19A2 intron 1 mutation c.204+2T>G has never been reported before. TRMA subjects are at risk of diabetic ketoacidosis during intercurrent disease and arrythmias. Thiamine supplementation has prevented hematological disorders over a few years in both pediatric subjects, and improved glycaemic control of diabetes mellitus. Patient 1 was suffering from hearing loss and rod‐cone dystrophy at the time of diagnosis, however, she was unresponsive to thiamine substitution. Our patient 2 developed the hearing loss despite the early thiamine substitution, however no visual disorder had developed. The novel mutation described here extends the list of SLC19A2 mutations causing TRMA.     

Congenital chloride diarrhea in Korean children: novel mutations and genetic characteristics

Congenital chloride diarrhea (CLD, OMIM#214700) is an autosomal recessive disorder caused by mutations in the solute carrier family 26 member 3 (SLC26A3) gene, which encodes an intestinal chloride/bicarbonate exchanger. While more than 50 mutations have been identified throughout the world, there have been no data on the genetic characteristics of the patients of East Asian ethnic origin. In this study, we performed genetic analysis by direct sequencing of the 20 exons and parts of exon–intron boundaries of the SLC26A3 gene in eight patients of Korean origin with non-consanguineous parents. We identified three novel mutations, including two splice-site mutations (c.2063-1G>T in intron 18, c.1047+3 A>C in intron 12) and one missense mutation (p.Ser134Asn in exon 5). One previously identified mutation was also found (p.Pro131Leu in exon 5). The most common mutation was c.2063-1G>T, which was found in at least one allele of all patients. Conclusion: This is the first report to demonstrate the genetic background of CLD in a single ethnic group of East Asian descent. The c.2063-1G>T mutation could be suggested as a founder mutation in Korean population so that the targeting sequencing for the mutation would be a cost-efficient screening method to confirm a diagnosis of CLD in patients of Korean descent.     

中国X连锁无丙种球蛋白血症40例基因型表型相关性分析

目的 通过中国X连锁无丙种球蛋白血症（XLA）患儿临床表现、免疫功能评价、Bruton′s 酪氨酸激酶（BTK）的表达及BTK基因突变分析,分析基因型和表型间可能存在的关系。 方法 选取拟诊为XLA患儿,使用抗BTK单克隆抗体通过流式细胞技术分析单核细胞BTK蛋白表达。采用RT-PCR获得患儿cDNA,使用8对不同引物分2步扩增BTK cDNA,PCR产物测序。突变结果通过对DNA 外显子相应部位扩增、测序证实。并对确诊XLA患儿的母亲及家族中部分亲属进行BTK蛋白表达和BTK基因分析。 结果 ①40/50例原发性低丙种球蛋白血症患儿经BTK基因突变分析确诊为XLA,以错义突变（16例,40.0%）和无义突变（13例,32.5%)为主。②突变类型为错义突变的患儿平均起病年龄为（1.4±1.1）岁,其他突变类型患儿为（1.4±0.7）岁,差异无统计学意义（P=0.45）。错义突变的发生率随年龄的增长呈上升趋势,无义突变的发生率呈下降趋势。③34/40例（85.0%）B细胞<0.1%;4例（10.0%）B细胞在1%~2%,其中错义突变2例,无义突变1例, 剪接突变1例;2例（5.0%）B细胞为2%,均为错义突变。④血清IgG<3 g·L-1患儿BTK基因突变类型以错义突变和无义突变为主。⑤错义突变患儿BTK蛋白表达水平与其他突变类型无显著差异。⑥6/21例（28.6%）2031C/T多态性患儿伴有严重的关节炎,3/19例（15.8％）无多态性患儿有关节炎表现。⑦28/32例（87.5%）XLA患儿母亲为BTK基因杂合型。 结论 错义突变可能与确诊年龄较大有关,且某些位点的错义突变可能与较高的外周血B细胞数量和血清IgG水平及正常的BTK蛋白表达水平有关。BTK基因多态性（2031C/T）可能增加关节炎的风险。     

广西地区β-地中海贫血的基因型与临床型的关系

我们分析４９例无亲缘关系的β－地中海贫血双重杂合子或纯合子的基因突变类型和临床表现。检出１０种突变类型，发现５例复合东南亚缺失型α－地中海贫血、６例复合Ｇｙ启动予－１５８ｎｔ（Ｃ→Ｔ）突变。根据这些患者的血红蛋白量，可将他们分成轻、中、重度贫血。２例β＋纯合子表现为轻度贫血；５例复合东南亚缺失型α－地中海贫血，６例复合Ｇｙ启动子－１５８ｎｔ（Ｃ→Ｔ）的患者均表现为中度贫血。这三种类型临床上表现为中间型β－地中海贫血，大多数单纯的Ｂ１与Ｂ０双重杂合子和β０纯合子表现为重型β－地中海贫血。     

生长激素受体基因突变与非生长激素缺乏性矮身材的相关研究

目的了解生长激素受体（GHR）基因突变与非生长激素缺乏性矮小的相关性,以及GHR基因突变患儿的临床特点。方法（1）选择47例（男33例,女14例,年龄2—16岁）非生长激素缺乏而又显著矮小的患儿作为研究对象;80例身高正常的儿童（男49例,女31例,年龄1—17岁）作为对照组。（2）应用PCR-SSCP和基因测序技术检测GHR突变。（3）通过家系成员和正常对照人群的基因分析以及氨基酸同源序列分析等,推测突变基因的性质。结果（1）在47例矮小患儿中有5例、4种不同的GHR基因突变：H56R、G148E、IVS6-30,-31CA〉TG和IVS8＋10G〉C。5例患儿均为杂合突变,杂合突变个体的检出频率为10．6％（5／47）。（2）对照组的基因分析显示这些突变非多态性改变,初步认为H56R和G148E突变可能对蛋白功能产生影响。（3）确定了1种多态性突变：G168G（GGA〉GGG）。该位点基因频率的分布在矮小儿童组和正常对照组之间的差异无统计学意义,但与西方白种人之间的差异有统计学意义。提示该突变可能是单核苷酸多态性改变,与身高没有相关关系。但该位点的等位基因存在人种的差异。结论非生长激素缺乏性矮身材患儿存在GHR基因杂合突变。     

Insight into B cell development and differentiation

The main topic of this article is B cell development and differentiation, with a special focus on the mechanisms and molecules that regulate the expression of humoral immunity. Molecular epidemiological analysis was performed on the genes responsible for the X-linked agammaglobu-linemia (XLA) phenotype of the majority of Italian patients and their distinct mutations were characterized. Mutations in Bruton's tyrosine kinase (BTK), a member of Tec Family of protein tyrosine kinases, have been found to be mainly responsible for XLA disease. The exact function of BTK in signal transduction is not yet known; thus, the specific role of BTK in receptor-dependent calcium signaling and the pro-antiapoptotic regulatory activity was addressed by transfecting RAMOS-1, a BTK-deficient human Burkitt's/B cell leukemia line with wild-type and mutant constructs. This work may provide clues about critical sites in the molecule and give support for gene therapy as a potential successful approach to XLA. Another aspect of this research is the identification and dissection of the molecular events that are likely to be directly related to the ability to express various isotypes of immunoglobulin with differing function and certain B cell immunodeficiency, mainly common variable disease and non-X-linked hyperIgM. B cell development and maturation steps in different compartments of the immune system are tracked by the analysis of cell-surface molecules and components of the signal transduction pathways, i.e. CD40, CD30, CD27, CD38, CD22 and CD24. A few components involved in B cell development, maturation and differentiation and their specific functional role are at least partially known, but these are far from fitting into an understandable pathway at present.     

Insight into B cell development and differentiation

The main topic of this article is B cell development and differentiation, with a special focus on the mechanisms and molecules that regulate the expression of humoral immunity. Molecular epidemiological analysis was performed on the genes responsible for the X-linked agammaglobulinemia (XLA) phenotype of the majority of Italian patients and their distinct mutations were characterized. Mutations in Bruton's tyrosine kinase (BTK), a member of Tec Family of protein tyrosine kinases, have been found to be mainly responsible for XLA disease. The exact function of BTK in signal transduction is not yet known; thus, the specific role of BTK in receptor-dependent calcium signaling and the pro-antiapoptotic regulatory activity was addressed by transfecting RAMOS-1, a BTK-deficient human Burkitt's/B cell leukemia line with wild-type and mutant constructs. This work may provide clues about critical sites in the molecule and give support for gene therapy as a potential successful approach to XLA. Another aspect of this research is the identification and dissection of the molecular events that are likely to be directly related to the ability to express various isotypes of immunoglobulin with differing function and certain B cell immunodeficiency, mainly common variable disease and non-X-linked hyperIgM. B cell development and maturation steps in different compartments of the immune system are tracked by the analysis of cell-surface molecules and components of the signal transduction pathways, i.e. CD40, CD30, CD27, CD38, CD22 and CD24. A few components involved in B cell development, maturation and differentiation and their specific functional role are at least partially known, but these are far from fitting into an understandable pathway at present.