发生在成视网膜细胞瘤蛋白大袋立体结构外的错义突变

目的:了解成视网膜细胞瘤(RB)患者RB1基因突变至RB发生中RB蛋白(pRB)的变化。方法: 提取RB患者的基因组DNA, PCR扩增后, SSCP/异源双链筛查RB1基因的启动子和全部27个外显子, 克隆测序鉴定突变, 并分析突变产物对pRB的影响。结果:RB患者RB1基因的外显子4存在着错义突变, 该突变发生在pRB的大袋立体结构外。RB患者RB1基因存在着不影响pRB大袋的生殖细胞性突变, 这是迄今为止第4例报道。结论:pRB氨基末端可能参与pRB对细胞的生长抑制。     

运用荧光定量多重PCR技术检测RB1基因突变

目的　建立一种半自动、简易、快速和不需放射性同位素技术,用以检测RB1 基因突变的方法。方法　应用包括扩增RB1 基因27 个外显子和启动区在内的荧光定量多重PCR 技术。将全基因分成若干组,每组3～7 对引物,同时含对照C4 引物并使用4 对外对照,分别为RB的缺体、单体、双倍体及三体。在测试标本中,一个片段的拷贝数根据比较对照与标本的荧光强度而获得。利用自动片段处理软件2.1 处理结果。结果　观察到小片段缺失、插入及外显子拷贝数缺失等突变。测序结果和RB瘤细胞杂合性丢失进一步证实荧光定量多重PCR 的筛查结果。结论　此法是筛查患者基因缺失、插入的一种快速、简易的方法。应用此法可查出约50% 的阳性病例。查出的突变不仅有小缺失、插入,也可发现用以往的方法所不能见到的外显子杂合性缺失病例。对临床基因缺陷的诊断有重要意义     

新名词新信息

设计婴儿：据报道，由于英国政府放宽了对人体胚胎（包括胚胎干细胞）研究的限制，世界上第1例“设计婴儿”将于明年3月前后诞生。这名“设计婴儿”是为了避免患先天性视网膜母细胞瘤婴儿的降生而经心营造的，部分视网膜母细胞瘤的发生是在合子（即受精卵）时期便决定了的，原因是精子或卵细胞带有一种有缺陷（或突变）的Rb基因，该基因的缺陷或突变使得成视网膜细胞无限增生，于是婴儿出生后必定罹患该疾患。     

肾上腺脑白质营养不良患者ABCD1基因第6外显子突变的初步分析

目的 检测肾上腺脑白质营养不良(adrenoleukodystrophy，ALD)(MIM300100)患者编码ALD蛋白的ABCD1基因[ATP-结合盒(ATP-binding cassette，ABC)超家族中D亚家族1]突变。方法 提取无亲缘关系的14例中国ALD患者及其中2例患者父母基因组DNA。聚合酶链反应(polymerase chainreaction，PCR)扩增ABCD1基因的第6外显子，以琼脂糖凝胶电泳鉴定PCR产物，PCR产物纯化后DNA直接测序。结果 证实3个患者的ABCD1基因第6外显子有突变，其中1例患者为5’末端上游第6个碱基C缺失(1489-6 del C)，推测该突变可能导致剪切错误；1例患者为错义突变1559T→A(L520Q)，这两例患者的母亲均为杂合突变。另1例患者为1548G→A(L516L)的同义突变。结论 首次报告了中国大陆ALD患者ABCD1基因突变．第6外显子无大片段缺失和重组突变。同一血缘族中可有不同的表型存在，提示是否有其它遗传或环境因素参与表型的表达。通过DNA测序方法亦证实其中2例患者之母为ABCD1基因的杂合子。     

parkin基因的一个新的点突变

目的：研究parkin基因外显子2-10点突变与散发性早发帕金森病发病的关系。方法：应用聚合酶链反应（polymerase chain reaction ，PCR）、琼脂糖电泳、单链构象多态性（single strand conformation polymorphism，SSCP）、DNA测序及限制性核酸内切酶酶切方法，检测了60例散发性早发帕金森病患者以及120名正常人外周血白细胞DNA的parkin基因外显子2-10点突变。结果：发现1例患者的parkin基因外显子2存在纯合突变（G237→C），限制性内切酶酶切证实，其它外显子未见突变，120名正常对照也未见突变。结论：parkin基因外显子存在点突变，可能与部分散发性早发帕金森病发病有关。     

RB1基因突变的筛查技术和发病风险评估

RB1基因早已被确认为视网膜母细胞瘤的唯一致病基因,也是人类第一个被分离的肿瘤抑制基因。视网膜母细胞瘤（RB）是婴幼儿最常见的眼科肿瘤,也是一种致死性肿瘤。RB1基因的突变检测,对RB患者及家系成员的分子诊断、筛查、产前诊断、植入前遗传学诊断及早期治疗均具有重要意义。迄今为止,RB1基因中所发现的突变类型包括点突变、缺失、插入、易位、剪接突变以及各种复杂突变,几乎遍布基因的启动子和27个外显子,甚至还有部分内含子突变。但RB1基因不存在突变热点,这大大增加了RB1基因突变筛查的难度。RB1基因的突变不仅存在于视网膜母细胞瘤患者中,而且见于许多恶性肿瘤。本文对RB1基因突变筛查技术和发病风险评估的最新研究进展作一简单综述。     

伴有低外显率的Rb基因点突变及其特征和意义

目的研究视网膜母细胞瘤患者（ＲＢ）低外显率的病因及其分子机理。方法收集ＲＢ先证者及其家庭成员的ＲＢ肿瘤与外周血，通过ＳＳＣＰ分析和ＤＮＡ序列测定检测Ｒｂ基因点突变，结合家系调查分析突变的特征及其与ＲＢ表型变化的关系。结果１５个低外显率的ＲＢ家系中部份家系存在特殊类型的Ｒｂ基因点突变，其中５个家系有Ａｒｇ６６１→Ｔｒｐ６６１突变，２个家系显示ｍＲＮＡ拼接位点异常，１个家系Ｒｂ基因启动子转录调控因子ＡＴＦ结合位点改变。结论ＲＢ低外显率并非完全随机发生的，与Ｒｂ基因突变的位置和性质有密切关系。     

先天性视网膜劈裂症基因突变分析

目的 阐明先天性视网膜劈裂症（X－linked juvenile retinoschisis,RS or XLRS)的发病机理,为建立基因诊断的方法提供理论依据。方法 采用聚合酶链反应－单链构象多态性分析,对6个独立XLRS病例进行了XLRS1基因突变筛选,并对发现的异常泳动带进行DNA测序,以明确突变位点;对发现的缺失突变进行Southern印迹证实。结果 在5个病例中发现基因突变。在家系1中发现缺失突变,家系中的4个患者均缺失了1、2和3外显子。在外显子4上检出3种异常泳动带,分别为3种突变,Glu72Lys,Glu72Gln,Gly70Ser。结论 XLRS1基因突变是导致中国人患RS的主要原因。本研究结果可直接应用于RS的遗传咨询和产前基因诊断。     

视网膜母细胞瘤基因对人骨肉瘤细胞株OS732的影响

目的 观察外源性N端截短的视网膜母细胞瘤（Rb)基因对骨肉瘤细胞株OS732的生长和细胞间缝隙连接信息通讯能力的影响。方法 构建N端截短的长度为1.65kb Rb基因的真核表达质粒,并用DOTAP将其导入骨肉瘤细胞株OS732。应用逆转录－聚合酶链反应（RT－PCR）和Northern blot检测Rb基因的表达;用细胞计数,流式细胞仪分析和软琼脂克隆形成试验观察OS732细胞的生成状况;用半定量RT－PCR法和罗氏黄荧光传输法检测细胞间缝隙连接信息通讯的能力。结果 转染N端截短的Rb基因后,OS732细胞内可检测到内源性和外源性Rb基因的mRNA表达。OS732细胞的形态发生改变,其生长速度减慢,软琼脂形成集落能力降低,细胞周期阻滞于G0－G1期;缝隙连接蛋白基因Gonnexin43的表达和细胞信息通讯能力增强。结论 N端截短的Rb基因可抑制骨肉瘤细胞株OS732的恶性生长表型以及增强细胞间信息通讯能力。     

妊娠期肝内胆汁淤积症中ABCB4基因外显子12突变的研究

目的探讨ABCB4基因外显子12的突变与妊娠期肝内胆汁淤积症（ICP）发病的关系。方法从31名ICP患者外周血标本中提取出基因组DNA,聚合酶链反应（PCR）扩增ABCB4基因外显子12,PCR产物经DNA序列测定检测突变情况。结果31名ICP患者均扩增出ABCB4基因外显子12的靶基因片断,未见外显子12的缺失,随机挑选20例标本测定外显子12的DNA序列,未发现突变。结论ABCB4基因外显子12的突变与中国皖南地区的ICP发生无关或关联很小,皖南地区ICP患者中可能存在其他的ABCB4基因突变热点。ABCB4基因的突变与中国人ICP发病的相关性仍应进行更大样本量的研究和更多外显子的筛查。     

Genotype-phenotype correlations in hereditary familial retinoblastoma

We studied 50 unrelated pedigrees with a family history of retinoblastoma (Rb) (165 carriers of a RB1 mutation) to delineate the spectrum of RB1 germline mutations in familial Rb and to identify genotype-phenotype correlations as well as putative modifiers. Patients were followed at Institut Curie and they were examined by an ophthalmologist, a pediatrician, and a geneticist. All cases of familial Rb were determined via genetic counseling. Clinical features included disease status, laterality, age at diagnosis, mutation type, follow-up, and disease-eye ratio (DER). To eliminate mosaic cases, first-generation carriers displaying low-penetrance (LP) Rb were excluded from the analysis. Complete penetrance was the rule for nonsense and frameshift mutations (25 families) and high penetrance was observed for large rearrangements (eight families). Promoter (two families) and missense (two families) mutations displayed heterogeneous phenotypes and LP. Variable penetrance was observed for splice abnormalities (13 families) and was explained by in/out of frame mutations or respect of functional domains. Surprisingly, two families with the LP g.45867G>T/IVS6+1G>T mutation presented data that conflicted with the data reported in previous publications, as unaffected carriers had paternally inherited mutant alleles. Moreover, RNA analyses suggested that the lack of penetrance in unaffected carriers could be explained by an increase in expression levels of the wild-type allele. This observation prompted us to define a new class "3" of LP alleles. We believe this is the first large-scale study of familial Rb with a high level of homogeneity in the clinical and genetic analysis of patients and their relatives, thereby allowing for reliable intrafamilial genotype-phenotype correlations. Our analysis suggests in some cases the influence of modifier factors probably involved in mRNA level regulation and/or pRB pathway regulation.     

Identification of 26 new constitutional RB1 gene mutations in Spanish, Colombian, and Cuban retinoblastoma patients

Constitutional mutations in the RB1 gene predispose to retinoblastoma development. Hence genetic screening of retinoblastoma patients and relatives is important for genetic counseling purposes. In addition, RB1 gene mutation studies may help decipher the molecular mechanisms leading to tumors with different degrees of penetrance or expressivity. In the course of genetically screening of 107 hereditary and non-hereditary retinoblastoma patients (11 familiar bilateral, 4 familiar unilateral, 49 sporadic bilateral and 43 sporadic unilateral) and kindred from Spain, Colombia and Cuba, using direct PCR sequencing, we observed 45 distinct mutations and four RB1 deletions in 53 patients (9 familiar bilateral, 2 familiar unilateral, 31 sporadic bilateral and 11 sporadic unilateral). Most of these mutations (26/45, 57%) have not been reported before. In 32 patients, the predisposing mutations correspond to nonsense (mainly CpG transitions) and small insertions or deletions whose expected outcome is a truncated Rb protein that lacks the functional pockets and tail. Five single aminoacid replacements and seventeen mutations affecting splicing sites were also observed in retinoblastoma patients. Two of these sixteen mutations are of unclear pathogenic nature.     

Constitutional genomic instability, chromosome aberrations in tumor cells and retinoblastoma

Although retinoblastoma (Rb) is initiated as a result of biallelic inactivation of the RB1 gene, additional genetic events (M3) in tumor cells are indicative of their role in the full transformation of retinal cells. We investigated the constitutional genetic instability by fragile site (FS) expression studies and checked its relationship with loci of tumor cytogenetics in a series of 36 retinoblastoma patients (34 nonfamilial and 2 familial cases). Tumor cytogenetics revealed -13/+13, del/t(13)(q14) (50%), +1/del/t(1p/q) (65%), +6/i(6p) (60%), and del(16)(q13)/(q22 approximately q23) (60%). Conventional cytogenetics in leukocytes revealed constitutional del(13q14) in five unilateral Rb (URB) and one trilateral Rb (TRB). Constitutional del(16)(q22) and t(6;12) were also identified in two cases. Constitutional FS analysis showed a significant increase in the cellular fragility, with high prevalence at 13q14, 3p14, 6p23, 16q22 approximately q23, and 13q22 loci in retinoblastoma patients (P<0.05). Patients with constitutional del(13)(q14) demonstrated higher fragility than those with normal constitution. A strong correlation between loci of constitutional FSs and loci of recurrent chromosomal abnormalities in tumors strengthen and support the proposal that FS loci present as inherent genomic instability in retinoblastoma. The chromosomal changes and resultant genetic mutations, along with RB1 mutation events, probably contribute synergistically to the development and progression of Rb malignancy. Implementation of fluorescence in situ hybridization to nonfamilial Rb on a large scale (113 cases) could detect constitutional RB1 deletion in 12.3% of cases, with equally higher incidence in URB (14.7%) and bilateral Rb (13.6%), demonstrating that the true prevalence of patients with predisposition to RB1 mutation in sporadic URB is definitely higher in our populations. Also, higher incidence of constitutional RB1 deletion mosaicism in unilateral than in bilateral Rb indicates that the constitutional genetic mosaicism in URB should be given serious consideration during genetic counseling.     

Comprehensive screening for constitutional RB1 mutations by DHPLC and QMPSF

Constitutional mutations of the RB1 gene are associated with a predisposition to retinoblastoma. It is essential to identify these mutations to provide appropriate genetic counseling in retinoblastoma patients, but this represents an extremely challenging task, as the vast majority of mutations are unique and spread over the entire coding sequence. Since 2001, we have implemented RB1 testing on a routine basis as part of the clinical management of retinoblastoma. As most screening techniques do not meet the requirements for efficient RB1 testing, we have devised a semi-automated denaturing high-performance liquid chromatography (DHPLC) method for point mutation detection combined with a quantitative multiplex PCR of short fluorescent fragments (QMPSF) approach to screen for gene rearrangements. We report the results of this comprehensive screening of all exons and promoter of RB1 in 192 unrelated patients, mostly of French origin. Among 102 bilateral and/or familial cases and 90 unilateral sporadic probands, mutations were identified in 83 (81.5%) and 5 (5.5%) cases, respectively. A total of 43 mutations have not been previously reported. The mutational spectrum was found to be significantly different from previous published series, displaying a surprising amount of splice mutations and large deletions. This study demonstrates the reliability of DHPLC for RB1 analysis, but also illustrates the need for a deletion scanning approach. Finally, considering the benefits to retinoblastoma patients, RB1 testing should be widely implemented in routine healthcare because our study clearly illustrates its feasibility.     

Two independent RB1-inactivating mutations in peripheral blood DNA of a hereditary retinoblastoma patient

We report the presence of a hemizygous inactivating germ-line RB1 mutation (a recurrent g.78250C-->T transition, resulting in a stop codon in exon 17) in peripheral blood DNA from a patient with hereditary bilateral retinoblastoma. Hemizygosity was established by sequencing that showed no traces of the wild-type C nucleotide and by quantitative real-time PCR, which showed loss of one copy of exon 17. Genotyping of the RB1 locus with several polymorphic markers delineated a maximal deletion region between g.76875 and g.99426, including exons 15-17 and a large piece (21 kb) of intron 17. The heterozygosity for the mutation found in skin fibroblasts proves that the intragenic RB1 deletion probably took place in the definitive hematopoietic lineage of the patient. The presence of a null Rb-/- genotype in the hematopoietic cell lineage suggests that the white blood cells of the proband could be useful in the investigation of the role of complementary RBI family proteins in the control of the cell cycle.