原发性局灶节段性肾小球硬化患者ACTN4基因变异和多态性

目的 了解ACTN4基因变异和多态性在原发性局灶节段性肾小球硬化（FSGS）发病中的作用。 方法 选取FSGS患者82例，另设70例健康人作为对照组。盐析法提取外周血基因组DNA，PCR扩增后测序，与基因数据库进行匹配，寻找可能致病变异位点。氯酚法提取患者父母头发DNA，间接免疫荧光法检测患者肾组织辅肌动蛋白4(α-actinin-4)表达水平。单核苷酸多态（SNP）位点经Hardy-Weinberg平衡检验后行基因频率、基因型和临床表型关联分析。 结果 发现1例患者单核苷酸变异184T>A(Ser62Thr)，1例5’UTR变异1-34C>T。对照组和患者父母未发现相同变异。1个疾病易感SNP位点484+87C>G。变异者肾组织α-actinin 4表达水平分别较对照组和非变异FSGS组下降。变异基因型和野生基因型尿蛋白量（24 h）的差异有统计学意义[（7.90±1.60 ）比(4.50±0.46) g/24 h， P ＜ 0.01]。此外，还发现6个新的变异和另1个SNP位点，但未引起氨基酸改变。 结论 原发性FSGS患者中存在ACTN4基因变异位点和疾病易感SNP位点。ACTN4基因变异在原发性FSGS发病中可能起重要作用。     

局灶节段性肾小球硬化患者致病基因突变检测

目的对散发性或家族性局灶节段性肾小球硬化（focal segmental glomerulosclerosis,FSGS）患者进行FSGS致病基因热点突变进行筛查,了解这些热点突变在我国FSGS患者的发生情况。方法研究对象为我院经肾脏活检确诊的40例FSGS散发病例及一个22人的FSGS家系LF-01。收集散发病例的外周血,采用盐析法提取基因组DNA;对LF-01家系进行调查,收集实验室检测数据,并留存外周血提取基因组DNA。对40例散发病例及所有家系成员进行ACTN4第8外显子,TRPC6第2、5、12、13外显子和INF2基因2、3、4外显子筛查,通过PCR扩增外显子后,直接测序进行基因突变检测。结果LF-01家系共9人为患病或可能患病状态,该家系表现为不完全外显遗传模型。40例散发FSGS患者,平均发病年龄37岁,男女比例为26：14,其中22例患者临床表现为肾病综合征。我们对所有样本进行了ACTN4第8外显子,TRPC6第2、5、12、13外显子和INF2基因2、3、4外显子筛查,均未发现有已知的基因突变。结论国外报道的FSGS致病基因的热点突变ACTN4、TRPC6和INF2可能不是中国汉族人群FSGS的致病基因。     

局灶节段性肾小球硬化相关基因研究进展

综述与局灶节段性肾小球硬化发病有关的相关基因研究的新进展。家族性FSGS的致病基因包括 :NPHS1,NPHS2 ,ACTN4,CD2AP(鼠 )。散发性FSGS致病基因mtDNA3 2 43A→G突变 ,NPHS2 ,PON1等。     

局灶节段性肾小球硬化相关基因研究进展

综述与局灶节段性肾小球硬化发病有关的相关基因研究的新进展。家族性FSGS的致病基因包括：NPHS1，NPHS2，ACTN4，CD2AP(鼠)。散发性FSGS致病基因mtDNA3243A→G突变，NPHS2，PON1等。     

迟发性家族性局灶节段肾小球硬化的足细胞分子基因突变研究

目的 了解迟发性家族性局灶节段肾小球硬化（FSGS）的足细胞分子基因致病突变特点。 方法 研究对象为上海瑞金医院肾脏科1997年9月至2007年10月收集的31个迟发性家族性FSGS家系。诊断标准：（1）成员年龄大于12岁；（2）1个家系中有2例或2例以上患者经肾活检证实为FSGS，或家系成员中有1例肾活检证实为FSGS，另有1例成员有蛋白尿或肾功能不全。100例健康人为对照组。外周血基因组DNA 经PCR扩增后直接对NPHS2、ACTN4、TRPC6基因行测序分析。 结果 发现ACTN4基因新错义突变L316P，该家系患病成员起病年龄平均（38.7±7.4）岁，肾功能损害进展相对缓慢，家系3例患病成员均为突变杂合子。发现TRPC6基因新杂合错义突变Q889K，该家系患者起病年龄平均（38.0±4.2）岁，肾功能损害进展也较缓慢，家系中临床表现存在个体差异，家系中3例患病成员均为突变杂合子。发现TRPC6静止突变G467G。所有家系中未发现NPHS2致病突变。健康对照组200条染色体亦未发现以上突变。 结论 在31例迟发性FSGS家系中发现2个家系携带致病相关突变：ACTN4新突变L316P和TRPC6新突变Q889K。在中国人群家族性迟发性FSGS中，ACTN4及TRPC6基因突变是致病原因之一，尚未发现NPHS2相关致病突变。     

薄基底膜肾病并发局灶节段性肾小球硬化症一家系的COL4A3和COL4A4基因突变分析

目的 探讨薄基底膜肾病(TBMN)合并局灶节段性肾小球硬化症(FSGS)的遗传学机制.方法 对一病理学诊断为TBMN合并FSGS患者及其家系的COL4A3和COL4A4基因突变,应用与COL4A3和COL4A4基因连锁的微卫星标记连锁分析方法进行分析.PCR扩增COIAA3和COL4A4全部98个外显子后,直接测序筛查突变.同时测序排除已为公认的FSGS相关基因NPHS1、NPHS2、WT1、TRPC6、ACTN4、CD2AP突变导致FSGS的可能.结果 微卫星标记连锁分析显示此家系与COL4A3和COL4A4基因连锁.直接测序在此家系中发现疾病患者COL4A4基因1214位的鸟嘌呤突变为腺嘌呤,导致Ⅳ型胶原α4链第405位甘氨酸突变为谷氨酸,并且发现COL4A3基因一多态性IVS1-4C＞T.此多态性随疾病分布,可能与致病相关.未发现FSGS相关基因的突变.结论 此家系是在TBMN的基础上发生FSGS.Ⅳ型胶原α4链突变及随疾病分布的基因多态性是否导致TBMN合并FSGS或使其易感性增加尚待更多家系进一步研究.     

中国汉族人3个家族性激素耐药型肾病综合征家系WT1和PLCE1基因突变分析

目的 分析中国汉族人家族性激素耐药型肾病综合征（SRNS）家系WT1和PLCE1基因突变及其特点。 方法 研究对象为A、B、C 3个汉族人SRNS家系的先证者（已除外NPHS2基因突变）及其父母,A、B 2个家系先证者的姐姐,50例尿检正常的汉族成年人作为对照人群。取所有研究对象外周静脉血3 ml,提取基因组DNA,PCR扩增WT1基因全部10个外显子和PLCE1基因全部31个编码外显子及其周围的部分内含子,应用直接DNA序列测定法和限制性片段长度多态性PCR（RFLP-PCR）分析法检测WT1和PLCE1基因变异。 结果 未发现WT1和PLCE1基因的致病突变。但是,在3个SRNS家系的先证者检测到3个WT1基因多态性：126C>T（P42P）、IVS5－64A>G和903A>G（R300R）,其中IVS5－64A>G为新发现的WT1基因多态性,126C>T和903A>G已见文献报道;还检测到13个PLCE1基因多态性 －134A>G、810T>C（C270C）、960G>A（E320E）、IVS11－28C>G、IVS15+26A>C、4724G>C（R1575P）、IVS20+40C>T、IVS21+64G>A、IVS22－26T>A、5320C>T（T1777I）、5780A>G（H1927R）、IVS27+24A>G和IVS31+48_49insT,其中IVS22－26T>A为新发现的PLCE1基因多态性,其余12个PLCE1基因多态性已见公布。 结论 WT1和PLCE1基因突变不是本研究3个中国汉族人家族性SRNS家系的主要致病原因。     

尿足细胞及其相关分子在肾小球疾病中的表达

目的：探讨尿液检测局灶节段性肾小球硬化足细胞损伤与其他足细胞病之间的特点和差异。方法：入选原发性局灶节段性肾小球硬化（KSGS）患者54例,膜性肾病（MN）23例及微小病变（MCD）12例,正常对照20例。免疫荧光法计数尿足细胞,荧光实时定量PCR法定量尿沉渣足细胞相关分子nephrin、podocin、synaptopodin mRNA的表达水平,Western印迹法检测尿液WilmsTumor1（WT1）蛋白水平,免疫荧光法检测肾脏组织podocalyxin的表达及分布。结果：（1）FSGS组、MN组、MCD组和对照组尿足细胞阳性率分别是63％、34．8％、33．3％和0,FSGS组与其余各组相比差异均有统计学意义（P〈0．05）。FSGS组足细胞脱落数目显著高于MCD组、MN组和对照组（P〈0．05）,伴足细胞尿FSGS患者与不伴足细胞尿FS—GS患者相比,24h尿蛋白和血清白蛋白（Alb）差异均有统计学意义（P〈0．05）。（2）FSGS组尿沉渣足细胞nephrin mRNA表达水平显著高于MCD和MN组（P〈0．05）;FSGS组尿沉渣足细胞podocinmRNA表达显著高于MCD组（P〈0．05）,与MN组相比有升高趋势但差异无统计学意义;尿沉渣足细胞synaptopodin mRNA表达各组间差异无统计学意义。尿沉渣足细胞nephrin、podocin．synaptopodin mRNA的表达与24h蛋白尿无相关性。（3）FSGS组尿WT1蛋白量显著高于MCD和MN组。部分足细胞阴性患者尿液检测到WT1分子。（4）FSC-S患者肾组织podocalyxin较对照组、MCD和MN有明显的节段缺失。结论：局灶节段性肾小球硬化病患者足细胞损伤严重,尿足细胞与FSGS疾病活动相关。尿沉渣足细胞nephrin mRNA表达可以把FSGS与MCD和MN区分开来,尿WT1蛋白可能是足细胞早期损伤指标。     

原发性局灶节段性肾小球硬化患者CD2AP基因突变的研究

目的了解原发性局灶节段性肾小球硬化（FSGS）患者CD2AP基因突变特点。方法研究对象为2001年至2004年我院收治的82例病理确诊为FSGS患者，年龄12-76岁，男性43例，女性39例，临床诊断为肾病综合征（NS）者55例，非NS27例；60例健康正常人为对照组。外周血基因组DNAPCR扩增后直接测序。冰冻切片免疫荧光双染色，激光共聚焦显微镜采集图像检测突变患者肾组织中CD2AP和podocin蛋白的表达。结果（1）发现2个CD2AP外显子突变，1个为2号外显子160G〉A杂合突变，造成第54位氨基酸由缬氨酸变为异亮氨酸（V54I），该患者为非NS患者，已出现肾功能不全。另1个为4号外显子358A〉G杂合突变，造成第120位氨基酸由异亮氨酸变为缬氨酸（1120V），该患者为NS患者，曾复发2次，目前肾功能尚正常。正常对照120条染色体中未发现同样突变。查阅文献和基因库，未发现相同突变报道。（2）CD2AP外显子突变患者肾小球内CD2AP表达明显减低，同时伴有podocin表达的降低。（3）发现1个启动子区突变、2个内含子突变和8个SNP位点，其中一个单核苷酸多态性（SNP）位点以往未见报道。结论CD2AP突变可能是原发性FSGS的致病原因之一。CD2AP外显子突变可导致CD2AP蛋白表达减少，并影响podocin的表达。     

hMLH1/hMSH2基因启动子变异在遗传性非息肉病性结直肠癌发生中的作用

目的 探讨hMLH1及hMSH2基因启动子变异在遗传性非息肉病性结直肠癌(HNPCC)发生中的作用。方法 PCR法扩增25例HNPCC患、20例散发性结直肠癌和10例非肿瘤患的hMLH1及hMSH2基因启动子序列，对PCR产物进行测序。对发现携带突变患的肿瘤标本进行hMLH1及hMSH2基因表达研究和微卫星不稳定(MSI)检测，同时用测序方法检测该患hMLH1及hMSH2基因编码序列的改变。结果55例检测样本中，C3．1及C3．2发现hMLH1启动子在-342位和-337位2处A插入变异，免疫组化检测该患hMLH1表达阴性，肿瘤MSI检测为MSI—H，而编码序列的检测未发现异常。结论 hMLH1／hMSH2基因启动子种系突变可能导致该基因的不表达，从而导致HNPCC结直肠癌的发生。错配修复基因编码序列正常的HNPCC患中可能存在该基因启动子突变。     

Focal and segmental glomerulosclerosis in mice with podocyte-specific expression of mutant alpha-actinin-4

Mutations in the gene encoding alpha-actinin-4 (ACTN4), an actin crosslinking protein, are associated with a form of autosomal dominant focal segmental glomerulosclerosis (FSGS). To better study its progression, a transgenic mouse model was developed by expressing murine alpha-actinin-4 containing a mutation analogous to that affecting a human FSGS family in a podocyte-specific manner using the murine nephrin promoter. Consistent with human ACTN4-associated FSGS, which shows incomplete penetrance, a proportion of the transgenic mice exhibited significant albuminuria (8 of 18), while the overall average systolic BP was elevated in both proteinuric and non-proteinuric ACTN4-mutant mice. Immunofluorescence confirmed podocyte-specific expression of mutant alpha-actinin-4, and real-time RT-PCR revealed that HA-ACTN4 mRNA levels were higher in proteinuric versus non-proteinuric ACTN4-mutant mice. Only proteinuric mice exhibited histologic features consistent with human ACTN4-associated FSGS, including segmental sclerosis and tuft adhesion of some glomeruli, tubular dilatation, mesangial matrix expansion, as well as regions of podocyte vacuolization and foot process fusion. Consistent with such podocyte damage, proteinuric ACTN4-mutant kidneys exhibited significantly reduced mRNA and protein levels of the slit diaphragm component, nephrin. This newly developed mouse model of human ACTN4-associated FSGS suggests a cause-and-effect relationship between actin cytoskeleton dysregulation by mutant alpha-actinin-4 and the deterioration of the nephrin-supported slit diaphragm complex.     

The genetic basis of FSGS and steroid-resistant nephrosis

Studies of Mendelian forms of focal segmental glomerulosclerosis (FSGS) and nephrotic syndrome have provided new insights into the mechanism of these diseases. Congenital nephrotic syndrome and familial forms of FSGS form a spectrum of podocyte diseases of varying severity and age of onset. Mutations in both nephrin gene (NPHS1) alleles lead to congenital nephrosis, podocyte foot process efacement, and loss of slit-diaphragm structure. Mutations in both podocin gene (NPHS2) alleles lead to a wide range of human disease, from childhood-onset steroid-resistant FSGS and minimal change disease to adult-onset FSGS. Dominantly inherited mutations in ACTN4, the alpha-actinin-4 gene, can lead to a slowly progressive adult-onset form of FSGS. In addition, FSGS is observed as part of several rare multisystem inherited syndromes. Here we review recent progress in understanding the genetic basis of FSGS in humans.     

Mutational and Biological Analysis of alpha-actinin-4 in focal segmental glomerulosclerosis

Mutations in the alpha-actinin-4 gene (ACTN4) cause an autosomal dominant form of focal segmental glomerulosclerosis (FSGS). A mutational analysis was performed of ACTN4 in DNA from probands with a family history of FSGS as well as in individuals with nonfamilial FSGS. The possible contribution of noncoding variation in ACTN4 to the development of FSGS also was assessed. Multiple nucleotide variants were identified in coding and noncoding sequence. The segregation of nonsynonymous coding sequence variants was examined in the relevant families. Only a small number of nucleotide changes that seemed likely to be causing (or contributing to) disease were identified. Sequence changes that predicted I149del, W59R, V801M, R348Q, R837Q, and R310Q changes were identified. For studying their biologic relevance and their potential roles in the pathogenesis of FSGS, these variants were expressed as GFP-fusion proteins in cultured podocytes. F-actin binding assays also were performed. Three of these variants (W59R, I149del, and V801M) showed clear cellular mislocalization in the form of aggregates adjacent to the nucleus. Two of these mislocalized variants (W59R and I149del) also showed an increased actin-binding activity. The I149del mutation segregated with disease; W59R was found to be a de novo mutation in the proband. A total of five ACTN4 mutations that are believed to be disease causing (three reported previously and two novel) as well as a number of variants with unclear contribution to disease now have been identified. The possibility that some of these other variants increase the susceptibility to FSGS cannot be excluded. ACTN4 mutations seem to account for approximately 4% of familial FSGS.     

Analysis of mutations in alpha-actinin 4 and podocin genes of patients with chronic renal failure due to sporadic focal segmental glomerulosclerosis

Although the pathogenesis of idiopathic focal segmental glomerulosclerosis (FSGS) may be heterogeneous, autosomal dominant and recessive forms of FSGS are recognized. Recently, mutations in alpha-actinin 4 (ACTN4) and podocin genes were reported in patients with such familial FSGS. However, whether mutations in ACTN4 and podocin genes are associated with sporadic FSGS has not been determined. In the present study, we clarified the relation between mutations in ACTN4 and podocin genes and sporadic FSGS. We analyzed these reported mutations in ACTN4 and podocin in five patients with chronic renal failure due to therapy-resistant FSGS by direct sequencing of polymerase chain reaction products of ACTN4 and podocin. We found a C to T transition at nucleotide 465 in the ACTN4 gene in all of patients, and a T to C transition at nucleotide 954 in exon eight of podocin gene in two of five patients, resulting in no amino acid substitutions. Other mutations were not found in ACTN4 and podocin genes. Our findings suggest that sporadic FSGS is a heterogeneous disease, since ACTN4 and podocin genes are not found in our patients with sporadic FSGS.     

FSGS-associated alpha-actinin-4 (K256E) impairs cytoskeletal dynamics in podocytes

Mutations in the ACTN4 gene, encoding the actin crosslinking protein alpha-actinin-4, are associated with a familial form of focal segmental glomerulosclerosis (FSGS). Mice with podocyte-specific expression of K256E alpha-actinin-4 develop foot process effacement and glomerulosclerosis, highlighting the importance of the cytoskeleton in podocyte structure and function. K256E alpha-actinin-4 exhibits increased affinity for F-actin. However, the downstream effects of this aberrant binding on podocyte dynamics remain unclear. Wild-type and K256E alpha-actinin-4 were expressed in cultured podocytes via adenoviral infection to determine the effect of the mutation on alpha-actinin-4 subcellular localization and on cytoskeletal-dependent processes such as adhesion, spreading, migration, and formation of foot process-like peripheral projections. Wild-type alpha-actinin-4 was detected primarily in the Triton-soluble fraction of podocyte lysates and localized to membrane-associated cortical actin and focal adhesions, with some expression along stress fibers. Conversely, K256E alpha-actinin-4 was detected predominantly in the Triton-insoluble fraction, was excluded from cortical actin, and localized almost exclusively along stress fibers. Both wild-type and K256E alpha-actinin-4-expressing podocytes adhered equally to an extracellular matrix (collagen-I). However, podocytes expressing K256E alpha-actinin-4 showed a reduced ability to spread and migrate on collagen-I. Lastly, K256E alpha-actinin-4 expression reduced the mean number of actin-rich peripheral projections. Our data suggest that aberrant sequestering of K256E alpha-actinin-4 impairs podocyte spreading, motility, and reduces the number of peripheral projections. Such intrinsic cytoskeletal derangements may underlie initial podocyte damage and foot process effacement encountered in ACTN4-associated FSGS.     

Analysis of recessive CD2AP and ACTN4 mutations in steroid-resistant nephrotic syndrome

Mutations in podocyte genes have been identified in patients with steroid-resistant nephrotic syndrome (SRNS). Point mutations in the ACTN4 gene cause an autosomal dominant form of human focal segmental glomerular sclerosis (FSGS); however, reports of CD2AP mutations remain scarce. Based on the phenotype of Actn4 and Cd2ap null mice, we aimed to define the role of recessive CD2AP and ACTN4 mutations in a cohort of children with SRNS for which NPHS1, NPHS2, and PLCE1 mutations had been previously excluded. CD2AP and ACTN4 mutational analysis was performed in 42 children from 35 unrelated families. The median age of disease onset was 20 (range 0–102) months. Sixteen patients reached end-stage kidney disease at a median age of 84 (range 4–161) months. Renal histology showed FSGS lesions and minimal glomerular changes in 49% and 20% of patients, respectively. Microsatellite marker analysis excluded linkage to the CD2AP locus in 26 families and to the ACTN4 locus in 31 families. No disease-causing mutations were identified in the remaining families. Recessive CD2AP and ACTN4 mutations are rare in children with SRNS. The absence of mutations in this study suggests that there are other genetic causes of SRNS that still need to be identified.     

<Emphasis Type="Italic">NPHS2</Emphasis> mutation associated with recurrence of proteinuria after transplantation

Mutations in the NPHS2 gene encoding podocin are associated with steroid-resistant nephrotic syndrome (SRNS) in childhood. Patients usually present with focal segmental glomerulosclerosis (FSGS). It is unclear to what extent SRNS due to NPHS2 mutations predisposes to recurrence of proteinuria/FSGS after renal transplantation (RTx). A 4-year-old girl with infantile SRNS was started on peritoneal dialysis because of end-stage renal disease due to FSGS. Mutational screening of the patient and her parents revealed a novel single nucleotide deletion in exon 8 of the NHPS2 gene (948delT), for which the patient was homozygous and her parents confirmed heterozygous asymptomatic carriers. At the age of 4.5 years the patient received a renal graft from her mother. On day 7 after RTx, the patient developed progressive proteinuria (urine protein/creatinine ratio 2.4 g/g), which responded within 1 week to prednisone pulse therapy, an increased cyclosporin A dosage, and ramipril therapy. The patient has maintained stable graft function and no further recurrence of proteinuria has been observed. In conclusion, patients with SRNS due to NPHS2 mutations are not protected from recurrence of proteinuria after RTx. The quick response to increased immunosuppression in our patient suggests an immune-mediated pathomechanism for recurrence of proteinuria.