面肩肱型肌营养不良症发病机制的研究进展

面肩肱型肌营养不良症,是一种常染色体显性遗传疾病,至今尚未找到其致病基因。大部分面肩肱型肌营养不良症患者和4q35区域3.3-kb的串联重复序列Z4D4的整倍缺失紧密连锁,几乎所有面肩肱型肌营养不良症患者,Southern杂交片段小于35 kb(少于11个D4Z4重复序列),而正常人群该片段为350 kb(11-150个D4Z4重复序列)。通过分子生物学研究与生物信息学分析,在4q35区域内,排除了FRG1、FRG2、ALP、ANT1、DUX4、YY I、HMGB2及Nu-c lolin等几个可能的候选基因;有关肩肱型肌营养不良症发病机制的位置变异效应假说,需要更多的证据支持;另一假说认为,面肩肱型肌营养不良症患者,D4Z4区域内类似沉默子的序列与转录抑制复合物相结合,由于D4Z4的缺失,该复合物不能形成并导致D4Z4上游基因的过表达,有关基因的过表达通过某种不明机制导致FSHD疾病的发生;D4Z4的缺失使4qter在细胞核内的定位异常,使许多基因的表达不正常,从而引起一系列的病理变化,并最终导致FSHD疾病的发生,也是FSHD发病的可能性机制之一。FSHD的发病相关基因和发病机制的研究有待深入。     

面肩肱型肌营养不良症的基因诊断与遗传咨询

目的探讨疑似面肩肱型肌营养不良症的基因诊断及其在生育咨询中的指导作用。方法基因检测染色体4q35区域Eco RI/P13E—11片段长度及4q A/4q B位点分析。结果患者的一条4号染色体(4q35)亚端粒区多态性Eco RI/p13E-11片段长度缩短至25.0-kb(正常参考值为38.0-300-kb),为4q A型片段,另一条4q35Eco RI/p13E-11片段长度大于38.0-kb,确诊为面肩肱型肌营养不良症。结论 DNA诊断在对FSHD进行家系分析、获得明确的D4Z4重复单元缩短的遗传学结果的基础上,进行生育咨询指导,对预防出生缺陷有重要意义。     

汉族人群4q亚端粒区等位片段4qA和4qB的结构特征

目的研究中国人4q35亚端粒区等位片段4qA和4qB的结构特征,探讨其与面肩肱型肌营养不良症（facioscapulohumeral muscular dystrophy,FSHD）的内在联系。方法研究对象包括80名无血缘关系的健康成年人。低熔点胶包埋法抽提基因组DNA。同一样品分别进行EcoRⅠ酶切、EcoRⅠ/BlnⅠ双酶切和HindⅢ酶切,脉冲电场电泳分离,p13E-11、4qA和4qB探针Southern印迹,计算4qA/4qB的频率、基因型频率及各型EcoRⅠ片段的长度,SPSS13.0统计软件分析数据。结果4q亚端粒区4qA的频率（46.9%）与4qB（53.1%）基本相等（χ2=1.250,P〉0.05）,4qA/4qB杂合型频率明显高于纯合型频率（P〈0.05）,4qA型和4qB型EcoRⅠ片段长度分别为（115.8±11.9）kb和（98.3±8.6）kb,两者差异有统计学意义（t=23.04,P〈0.001）。8.8%（7/80）的个体检测到易位构型。2名个体出现4qB型短EcoRⅠ片段。结论正常中国人4q亚端粒区4qA和4qB的频率基本相等,杂合型频率明显高于纯合型频率。4qB型D4Z4缺失不致病。4qA和4qB型EcoRⅠ片段具有动态性变化特征。     

面肩肱型肌营养不良症的分子遗传学研究进展

面肩肱型肌营养不良症（factoscapulohumeral muscular dystrophy,FSHD)呈常染色体显性遗传。大多数致病基因定位于4q35,存在遗传异质性。发现与FSHD相关的DNA重组,即4q35上3．3kb串联重复单位呈不同拷贝数缺失。以p13E-11为探针检测EcoR I/Bln I双重消化的DNA片段,FSHD患者的消化片段通常小于正常人,从而进行有效的分子诊断。由于FSHD基因尚未鉴定与分子,FSHD的确切发病机理仍未阐明,提出有位置效应变异假说等。目前有一候选基因FRG1。与FSHD相关的DNA重组片段的大小与FSHD临床表型之间显著相关,可较好地解释FSHD患者广泛的临床变异性。     

4q35染色体内和间亚端粒重排:面肩胛骨肱骨肌营养不良的病因和诊断意义

面肩肿骨防骨肌营养不良（FSHD）是一种以面部、上肢带和上臂肌肉无力为主要特征的常染色体显胜神经肌肉疾病。本文作者通过探针P13E－11检测证实,FSHD的病因与短E。。RI片段有关。这种残留片段是4q35上申联排列的3．3kb重复单位（D4Z4）完整缺失的结果。尽管有深入的分析,但尚未识别出这种排列内的转录顺序。作者先前曾证明20％人群在4q35上这些重复已转换成IOq26上相似高度的同源重复基因座,而且在‘qss上的一种短的类似于10号染色体的排列也引起FSHD。作者报道的这些重复排列杂交结构,反映附加亚端粒的不稳定。3名正常人10…     

面肩肱型肌营养不良症基因诊断

目的 观察面肩肱型肌营养不良症(facioscapulohumeral muscular dystrophy，FSHD)患者p13E—11标记的4q35 EcoR Ⅰ／B1n Ⅰ片段分子量变化特点，对FSHD进行基因诊断。方法 提取基因组DNA，EcoR Ⅰ／B1n Ⅰ双酶切后进行脉冲凝胶电泳，用同位素标记的探针p13E—11进行Southern印迹，以小于38kb为诊断FSHD标准，观察4q35 EcoR Ⅰ／B1n Ⅰ片段分子量大小的分布。结果 FSHD组26例患者中，20例4q35 EcoR Ⅰ／B1n Ⅰ片段小于38kb，基因诊断阳性率为76．92％。FSHD亲属组12例，其中两例该片段小于38kb。对照组21人，该片段均大于38kb。结论 以小于38kb为诊断标准较满意，FSHD基因诊断阳性率与文献基本吻合。     

一例以智力低下为首发症状的面肩肱型肌营养不良患儿D4Z4区的变异分析

目的鉴定一例以智力障碍为首发症状的面肩肱型肌营养不良(facioscapulohumeral muscular dystrophy,FSHD)患儿4q35上D4Z4区域的致病变异。方法对患儿进行韦氏智力检测,并收集其临床资料进行综合分析。提取患儿及其父母的外周血DNA,先采用医学外显子组二代测序和拷贝数变异检测,之后应用分子梳法鉴定其D4Z4重复单元的缩短情况并鉴定其来源。结果患儿总体智商估计值为41,言语理解指数估计值为45,知觉推理指数估计值为520医学外显子组测序和拷贝数变异检测未发现患儿携带致病变异,分子梳检测结果表明患儿D4Z4区的长度为5.2kb,重复单元数为2,患儿的父母均未检测到相同的变异。结论D4Z4重复单元只有2个可能是患儿智力低下和FSHD的致病原因。分子梳检测能够鉴定此重复单元的数目和来源,有助于明确诊断。     

应用脉冲场电泳技术研究中国人4q35与10q26亚端粒区EcoRI片段的结构多态性

目的研究中国人4q35与10q26同源性EcoRⅠ片段的结构多态性,探讨该区域的可塑性、易位和体细胞嵌合现象及其与D4Z4重复单位缺失的关系.方法研究对象包括110名无血缘关系的健康成年人.低熔点胶包埋法抽提基因组DNA.同一样品分别进行EcoRⅠ酶切和EcoRⅠ/BlnⅠ双酶切, 脉冲场电泳分离,p13E-11探针Southern杂交,曲线拟合法计算分析EcoRⅠ片段的长度,SPSS11.0统计软件分析数据.结果 77.3%(85/110)的个体为标准构型,4q35 EcoRⅠ片段的长度均值为(87.9±3.3) kb,中位数为78.5 kb;10q26同源性片段的长度均值为(90.1±4.1) kb,中位数为73.0 kb;经t检验,两者差异无显著性(P>0.05).19.1%(21/110)的个体检测到易位构型,其中4q→10q易位和10q→4q易位分别为9.1%(10/110)和10.0%(11/110),经卡方检验,两种易位形式的频率基本相等(χ2=0.053,P>0.05).3.6%(4/110)的个体检测到体细胞嵌合片段.此外,14.5%(16/110)的个体检测到小于35 kb的10q26 EcoRⅠ短片段.结论正常中国人4q35和10q26 EcoRⅠ片段具有多态性和动态性变化特征,两者具有高度同源性.4q35-10q26易位是导致4q35区不稳定和D4Z4缺失的重要因素,体细胞嵌合现象的出现提示4q与10q区D4Z4的互换重组可能发生于有丝分裂过程中.     

应用脉冲场电泳技术研究中国人4q35与10q26亚端粒区EcoRⅠ片段的结构多态性

目的研究中国人4q35与10q26同源性EcoR片段的结构多态性,探讨该区域的可塑性、易位和体细胞嵌合现象及其与D4Z4重复单位缺失的关系。方法研究对象包括110名无血缘关系的健康成年人。低熔点胶包埋法抽提基因组DNA。同一样品分别进行EcoR酶切和EcoR/Bln双酶切,脉冲场电泳分离,p13E-11探针Southern杂交,曲线拟合法计算分析EcoR片段的长度,SPSS11.0统计软件分析数据。结果77.3%(85/110)的个体为标准构型,4q35EcoR片段的长度均值为(87.9±3.3)kb,中位数为78.5kb;10q26同源性片段的长度均值为(90.1±4.1)kb,中位数为73.0kb;经t检验,两者差异无显著性(P>0.05)。19.1%(21/110)的个体检测到易位构型,其中4q→10q易位和10q→4q易位分别为9.1%(10/110)和10.0%(11/110),经卡方检验,两种易位形式的频率基本相等(χ2=0.053,P>0.05)。3.6%(4/110)的个体检测到体细胞嵌合片段。此外,14.5%(16/110)的个体检测到小于35kb的10q26EcoR短片段。结论正常中国人4q35和10q26EcoR片段具有多态性和动态性变化特征,两者具有高度同源性。4q35-10q26易位是导致4q35区不稳定和D4Z4缺失的重要因素,体细胞嵌合现象的出现提示4q与10q区D4Z4的互换重组可能发生于有丝分裂过程中。     

BglⅡ-BlnⅠ剂量检测方法在面肩肱型肌营养不良症1A基因诊断中的应用

目的 通过检测染色体4q35和10q26之间的易位情况，进一步提高面肩肱型肌营养不良症1A(hcioscapulohumeral muscular dystrophy，FSHD1A)基因诊断的准确性。方法 应用Bgl Ⅱ-Bln Ⅰ剂量检测方法，对7例基因诊断阳性的FSHD症状前患者和5例基因诊断阴性而临床诊断为散发性FSHD患者的染色体4q35和10q26的易位状况进行分析。用Bgl Ⅱ和Bin Ⅰ酶切基因组DNA后行琼脂糖凝胶电泳，制备p13E-11探针并以α^-32P dCTP标记，进行Southern杂交及放射自显影。应用图像分析系统和薄层扫描仪对4q与10q杂交片段的信号强度进行定量分析，判断4q35和10q26的易位情况。结果 在基因诊断阳性的7例FSHD症状前患者中，1例发生了4q35至10q26的易位，有可能为假阳性基因诊断。在基因诊断阴性的5例散发性FSHD患者中，1例发生了10q26至4q35的易位，可能为假阴性基因诊断。其余10例未发现4q35和10q26之间的易位．结论 应用Bgl Ⅱ-Bln Ⅰ剂量检测方法，可以检出染色体4q35和10q26之间的易位，能够进一步提高FSHD1A基因诊断的准确性。     

Inter- and intrachromosomal sub-telomeric rearrangements on 4q35: implications for facioscapulohumeral muscular dystrophy (FSHD) aetiology and diagnosis

The autosomal dominant myopathy facioscapulohumeral muscular dystrophy (FSHD) is causally related to a short Eco RI fragment detected by probe p13E-11. This remnant fragment is the result of a deletion of an integral number of tandemly arrayed 3.3 kb repeat units (D4Z4) on 4q35. Despite intensive efforts, no transcribed sequences have been identified within this array. Previously, we have shown that these repeats on 4q35 have been exchanged for a similar highly homologous repeat locus on 10q26 in 20% of the population and that a short chromosome 10-like array on 4q35 also results in FSHD. Here, we describe the hybrid structure of some of these repeat arrays, reflecting additional sub-telomeric instability. In three healthy individuals carrying a 4-like repeat on chromosome 10 or vice versa, one repeat array was shown to consist of hybrid clusters of 4-derived and 10-derived repeat units. Moreover, employing pulsed field gel electrophoresis analysis, we identified two unrelated individuals carrying deletions of a chromosomal segment (p13E-11) proximal to the repeat locus. These deletions were not associated with FSHD. In one of these cases, however, an expansion of the deletion into the repeat array was observed in one of his children suffering from FSHD. These data provide additional evidence for instability of this sub-telomeric region and suggests that the length of the repeat, and not its intrinsic properties, is crucial to FSHD. Moreover, they are in agreement with the hypothesis that FSHD is caused by a position effect in which the repeat structure influences the expression of genes nearby. Therefore, the region deleted proximal to the repeat locus in healthy individuals can be instrumental to refine the critical region for FSHD1.      

Analysis of the tandem repeat locus D4Z4 associated with facioscapulohumeral muscular dystropothhy

The sequence of the tandem repeat sequence (D4Z4) associatedwith facioscapulohumeral muscular dystrophy (FSHD) has beendetermined: each copy of the 3.3 kb repeat contains two homeoboxesand two previously described repetitive sequences, LSau anda GC-rich low copy repeat designated hhspm3. By Southern blotting,FISH and isolation of cDNA and genomic clones we show that thereare repeat sequences similar to D4Z4 at other locations in thehuman genome. Southern blot analysis of primate genomic DNAindicates that the copy number of D4Z4-like repeats has increasedmarkedly within the last 25 million years. Two cDNA clones wereisolated and found to contain stop codons and frameshifts withinthe homeodomains. An STS was produced to the cDNAs and analysisof a somatic cell hybrid panel suggests they map to chromosome14. No cDNA clones mapping to the chromosome 4q35 D4Z4 repeatshave been Identified, although the possiblilty that they encodea protein cannot be ruled out. Although D4Z4 may not encodea protein, there is an association between deletions withinthis locus and FSHD. The D4Z4 repeats contain LSau repeats andare adjacent to 68 bp Sau3A repeats. Both of these sequencesare associated with heterochromatic regions of DNA, regionsknown to be involved in the phenomenon of position effect variegation.We postulate that deletion of D4Z4 sequences could produce aposition effect.     

Common epigenetic changes of D4Z4 in contraction‐dependent and contraction‐independent FSHD

Facioscapulohumeral muscular dystrophy (FSHD), caused by partial deletion of the D4Z4 macrosatellite repeat on chromosome 4q, has a complex genetic and epigenetic etiology. To develop FSHD, D4Z4 contraction needs to occur on a specific genetic background. Only contractions associated with the 4qA161 haplotype cause FSHD. In addition, contraction of the D4Z4 repeat in FSHD patients is associated with significant D4Z4 hypomethylation. To date, however, the methylation status of contracted repeats on nonpathogenic haplotypes has not been studied. We have performed a detailed methylation study of the D4Z4 repeat on chromosome 4q and on a highly homologous repeat on chromosome 10q. We show that patients with a D4Z4 deletion (FSHD1) have D4Z4‐restricted hypomethylation. Importantly, controls with a D4Z4 contraction on a nonpathogenic chromosome 4q haplotype or on chromosome 10q also demonstrate hypomethylation. In 15 FSHD families without D4Z4 contractions but with at least one 4qA161 haplotype (FSHD2), we observed D4Z4‐restricted hypomethylation on chromosomes 4q and 10q. This finding implies that a genetic defect resulting in D4Z4 hypomethylation underlies FSHD2. In conclusion, we describe two ways to develop FSHD: (1) contraction‐dependent or (2) contraction‐independent D4Z4 hypomethylation on the 4qA161 subtelomere. Hum Mutat 30:1–11, 2009. © 2009 Wiley‐Liss, Inc.     

Distinguishing the 4qA and 4qB variants is essential for the diagnosis of facioscapulohumeral muscular dystrophy in the Chinese population

Facioscapulohumeral muscular dystrophy (FSHD) is the third most common inherited muscular dystrophy with markedly clinical variability and complex genetic cause. Several reports pertaining to the Caucasian population have confirmed that there are 4qA and 4qB variants of the 4qter subtelomere, and FSHD is uniquely associated with the 4qA variant. However, few data relevant to the Chinese population have been published. In present paper, detailed clinical and genetic re-evaluations were performed in members of four special families who had been initially diagnosed as atypical or asymptomatic FSHD based only on the D4Z4 repeat length analysis. The FSHD-sized D4Z4 repeats in the probands from families 1, 2 and 3 were identified as 4qB variants. These patients were further confirmed as limb-girdle muscular dystrophy (LGMD2) or myotonic dystrophy (DM1) by molecular analyses. Specifically, we identified a 4qB variant on chromosome 10 in the healthy members of the fourth FSHD family with complex D4Z4 rearrangements of two exchanged repeat arrays. For the first time, we demonstrated in the Chinese population that D4Z4 contractions on the 4qB variant do not cause FSHD and 4qB variant on chromosome 10 might also represent intermediate structures in the transition from 4q to 10q. Furthermore, our results emphasize that D4Z4 repeat length analysis alone is not sufficient for the diagnosis of FSHD, especially when used as an exclusion criterion. This analysis should be accompanied by 4qA/4qB variant determination and integrated chromosome assignments, especially in patients with obscure and unclassified myopathies similar to atypical forms of FSHD.     

Evaluation of the facioscapulohumeral muscular dystrophy (FSHD1) phenotype in correlation to the concurrence of 4q35 and 10q26 fragments

Probe p13E-11 (locus D4F104S1) detects two highly homologous polymorphic loci on chromosomes 4q35 and 10q26. Previous reports in the literature have described a correlation of shortened 4q35-specific fragments and facioscapulohumeral muscular dystrophy (FSHD1). We have identified 30 FSHDI families (46 patients) carrying one short 4q35 and one short 10q26 fragment. The clinical data of these patients were compared with those of 47 families (131 patients) showing a single short 4q35 fragment, in order to evaluate a potentially modifying influence of shortened 10q26 fragments on the phenotype. According to our results, the polymorphic locus on 10q26 does not modify the FSHDI phenotype. The normal population (14%) and our FSHDI population (13%) did not significantly differ in the overall frequency of short polymorphic 10q26 fragments. The specificity of the p13E-11/EcoRI-BlnI test for FSHD1 was 100%.     

Methylation of the FSHD syndrome-linked subtelomeric repeat in normal and FSHD cell cultures and tissues.

Facioscapulohumeral muscular dystrophy (FSHD) has an unusual molecular etiology. In a putatively heterochromatic subtelomeric region of each chromosome 4 homologue (4q35), unaffected individuals have 11 to about 95 tandem copies of a complex 3.3-kb repeat (D4Z4). Most FSHD patients have less than 10 copies at one allelic 4q35. This has been proposed to lead to the loss of heterochromatinization and, thereby, inappropriate gene expression by position effects, explaining the dominant nature of FSHD and the role of a decreased number of copies of D4Z4 at 4q35 but not at 10q26. Consistent with the proposed heterochromatinization of this repeat, by Southern blot analysis, we found that SmaI, MluI, SacII, and EagI sites in D4Z4 are highly methylated in normal and FSHD cell lines and somatic tissues, including skeletal muscle. Like repeated DNA sequences in the juxtacentromeric heterochromatin of chromosomes 1, 9, and 16, D4Z4 was hypomethylated at numerous CpGs in sperm and in cell lines from patients with an unrelated DNA methyltransferase deficiency syndrome (ICF; immunodeficiency, centromeric region instability, facial anomalies) in contrast to its hypermethylation in non-ICF postnatal somatic tissues. Our data on FSHD samples suggest that the disease-associated 4q35 D4Z4 repeats, which constitute a small percentage of the total D4Z4 repeats, are not generally hypomethylated relative to the other repeats of this sequence. However, in individuals not affected with FSHD, the hypermethylation of tandem, high-copy-number D4Z4 repeats might help stabilize heterochromatinization at allelic 4q35 regions just as hypermethylation elsewhere in the genome has been linked to chromatin compaction.     

Monosomy of distal 4q does not cause facioscapulohumeral muscular dystrophy.

Facioscapulohumeral muscular dystrophy (FSHD) is a hereditary neuromuscular disorder transmitted in an autosomal dominant fashion. FSHD has been located by linkage analysis in the most distal part of chromosome 4q. The disease is associated with deletions within a 3.2 kb tandem repeat sequence, D4Z4. We have studied a family in which an abnormal chromosome 4 segregates through three generations in phenotypically normal subjects. This chromosome is the derivative of a (4;D or G) (q35;p12) translocation. Molecular analysis of the region 4q35 showed the absence of the segment ranging from the telomere to locus D4F104S1. Probe p13E-11 (D4F104S1), which detects polymorphic EcoRI fragments containing D4Z4, in Southern blot analysis showed only one allele in the carriers of the abnormal chromosome 4. Probe p13E-11 EcoRI fragments are contained in the subtelomeric region of 4q and their rearrangements associated with FSHD suggested that the gene responsible for the muscular dystrophy could be subject to a position effect variegation (PEV) because of its proximity to subtelomeric heterochromatin. The absence of the 4q telomeric region in our phenotypically normal cases indicates that haploinsufficiency of the region containing D4Z4 does not cause FSHD.     

Clinical and Genetic Analysis of Korean Patients with Facioscapulohumeral Muscular Dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominantly inherited muscular disorder, which is characterized by weakness of facial, shoulder and hip girdle, humeral, and anterior distal leg muscles. The FSHD gene has been mapped to 4q35 and a deletion of integral copies of a 3.3-kb DNA repeat motif named D4Z4 was known to be the genetic background of the disorder. Although FSHD is the second most common muscular dystrophy in adulthood, there were few reports on the genetically confirmed patients in Korea. Recently, we experienced four Korean patients with clinical features resembling FSHD. In order to confirm the diagnosis, conventional Southern blot (SB) analysis by using double digestion with EcoRI and BlnI and hybridization with p13E-11 probe was performed in three patients and newly developed long polymerase chain reaction (PCR) method was used for one patient because genomic DNA was not enough for conventional SB for this patient. All patients were demonstrated to have shortened D4Z4 repeats that were consistent with FSHD. Therefore, we could confirm the diagnosis of FSHD in four Korean patients and appropriate genetic counseling was done for the patients and their families. It is of note that long-PCR method could be a good alternative for conventional SB when D4Z4 repeats were less than 5.