Novel LMNA mutations in patients with Emery‐Dreifuss muscular dystrophy and functional characterization of four LMNA mutations

Mutations in LMNA cause a variety of diseases affecting striated muscle including autosomal Emery‐Dreifuss muscular dystrophy (EDMD), LMNA‐associated congenital muscular dystrophy (L‐CMD), and limb‐girdle muscular dystrophy type 1B (LGMD1B). Here, we describe novel and recurrent LMNA mutations identified in 50 patients from the United States and Canada, which is the first report of the distribution of LMNA mutations from a large cohort outside Europe. This augments the number of LMNA mutations known to cause EDMD by 16.5%, equating to an increase of 5.9% in the total known LMNA mutations. Eight patients presented with either p.R249W/Q or p.E358K mutations and an early onset EDMD phenotype: two mutations recently associated with L‐CMD. Importantly, 15 mutations are novel and include eight missense mutations (p.R189P, p.F206L, p.S268P, p.S295P, p.E361K, p.G449D, p.L454P, and p.W467R), three splice site mutations (c.IVS4 + 1G>A, c.IVS6 ? 2A>G, and c.IVS8 + 1G>A), one duplication/in frame insertion (p.R190dup), one deletion (p.Q355del), and two silent mutations (p.R119R and p.K270K). Analysis of 4 of our lamin A mutations showed that some caused nuclear deformations and lamin B redistribution in a mutation specific manner. Together, this study significantly augments the number of EDMD patients on the database and describes 15 novel mutations that underlie EDMD, which will contribute to establishing genotype–phenotype correlations. Hum Mutat 31:–16, 2011. © 2011 Wiley‐Liss, Inc.     

Cardiac dysrhythmias,cardiomyopathy and muscular dystrophy in patients with Emery-Dreifuss muscular dystrophy and limb-girdle muscular dystrophy type 1B

Emery-Dreifuss muscular dystrophy (EDMD) and limb-girdle muscular dystrophy type 1B (LGMD1B) are characterized by cardiac dysrhythmias, late-onset cardiomyopathy, slowly progressive skeletal myopathy and contractures of the neck, elbows and ankles. The causative mutation is either in the emerin gene (X-linked recessive EDMD) or lamin A/C gene (autosomal dominant EDMD2 or LGMD1B). We report three cases of EDMD, EDMD2 and LGMD1B. A 14-yr-old boy showed limitation of cervical flexion and contractures of both elbows and ankles. Sinus arrest with junctional escape beats was noted. He was diagnosed as X-linked recessive EDMD (MIM 310300). A 28-yr-old female showed severe wasting and weakness of humeroperoneal muscles. Marked limitation of cervical flexion and contractures of both elbows and ankles were noted. Varying degrees of AV block were noted. She was diagnosed as autosomal dominant EDMD2 (MIM 181350). A 41-yr-old female had contractures of both ankles and limb-girdle type muscular dystrophy. ECG revealed atrial tachycardia with high grade AV block. She was diagnosed as autosomal dominant LGMD1B (MIM 159001). Cardiac dysrhythmias in EDMD and LGMD1B include AV block, bradycardia, atrial tachycardia, atrial fibrillation, and atrial standstill, causing sudden death necessitating pacemaker implantation. Cardiologists should know about these unusual genetic diseases with conduction defects, especially in young adults.     

Novel and recurrent mutations in lamin A/C in patients with Emery‐Dreifuss muscular dystrophy

Emery‐Dreifuss muscular dystrophy (EDMD) is characterized by slowly progressive muscle wasting and weakness; early contractures of the elbows, Achilles tendons, and spine; and cardiomyopathy associated with cardiac conduction defects. Clinically indistinguishable X‐linked and autosomal forms of EDMD have been described. Mutations in the STA gene, encoding the nuclear envelope protein emerin, are responsible for X‐linked EDMD, while mutations in the LMNA gene encoding lamins A and C by alternative splicing have been found in patients with autosomal dominant, autosomal recessive, and sporadic forms of EDMD. We report mutations in LMNA found in four familial and seven sporadic cases of EDMD, including seven novel mutations. Nine missense mutations and two small in‐frame deletions were detected distributed throughout the gene. Most mutations (7/11) were detected within the LMNA exons encoding the central rod domain common to both lamins A/C. All of these missense mutations alter residues in the lamin A/C proteins conserved throughout evolution, implying an essential structural and/or functional role of these residues. One severely affected patient possesed two mutations, one specific to lamin A that may modify the phenotype of this patient. Mutations in LMNA were frequently identified among patients with sporadic and familial forms of EDMD. Further studies are needed to identify the factors modifying disease phenotype among patients harboring mutations within lamin A/C and to determine the effect of various mutations on lamin A/C structure and function. © 2001 Wiley‐Liss, Inc.     

Laminopathies in Russian families

Mutations in LMNA gene produce a wide spectrum of disorders called laminopathies. In this article, the first cases of laminopathies from Russia are reported. In 10 unrelated families, 9 different mutations were identified: Asp47His, Gly232Arg, c.[781_783delAAG, 781insGTGGAGCAGTATAAGAAA], Arg249Gln (in two families), Arg377His, Arg541His, Ala350Pro, Leu52Pro, and Gly635Asp. Mutations Arg249Gln, Arg377His, and Arg541His were reported previously, others are novel. Four cases present de novo mutations, among them two cases with Arg249Gln are found. Because this mutation occurred de novo also in other reported cases, a mutational 'hot spot' was supposed. Three phenotypes were observed: autosomal dominant (AD) Emery–Dreifuss muscular dystrophy (EDMD), limb-girdle MD type 1B, and AD dilated cardiomyopathy with conduction defect type 1A (DCM1A). Atypical clinical presentations were a very severe EDMD and an infantile DCM1A.     

Cardiac involvement in Emery-Dreifuss muscular dystrophy

Emery-Dreifuss muscular dystrophy (EDMD) is a common form of muscular dystrophy frequently involving cardiac muscle, thus leading to dilated cardiomyopathy. Clinical outcome and prognosis is frequently determined by the involvement of the cardiac conduction system causing symptomatic bradyarrhythmias, as well as tachyarrhythmias and, if untreated, frequent sudden cardiac death. Typical features of the cardiac involvement of EDMD are presented, caused by a novel missense mutation in the splice receptor sequence of intron 6 of the LMNA gene on chromosome 1, encoding for the lamin A/C gene, consistent with the autosomal dominant form of EDMD.     

Autosomal recessive limb-girdle and Miyoshi muscular dystrophies in the Netherlands: The clinical and molecular spectrum of 244 patients

In this retrospective study, we conducted a clinico-genetic analysis of patients with autosomal recessive limb-girdle muscular dystrophy (LGMD) and Miyoshi muscular dystrophy (MMD). Patients were identified at the tertiary referral centre for DNA diagnosis in the Netherlands and included if they carried two mutations in CAPN3, DYSF, SGCG, SGCA, SGCB, SGCD, TRIM32, FKRP or ANO5 gene. DNA was screened by direct sequencing and multiplex ligand-dependent probe amplification (MLPA) analysis. A total of 244 patients was identified; 68 LGMDR1/LGMD2A patients with CAPN3 mutations (28%), 67 sarcoglycanopathy patients (LGMDR3-5/LGMD2C-E) (27%), 64 LGMDR12/LGMD2L and MMD3 patients with ANO5 mutations (26%), 25 LGMDR2/LGMD2B and MMD1 with DYSF mutations (10%), 21 LGMDR9/LGMD2I with FKRP mutations (9%) and one LGMDR8/LGMD2H patient with TRIM32 mutations (<1%). The estimated minimum prevalence of AR-LGMD and MMD in the Netherlands amounted to 14.4 × 10⁻⁶. Thirty-three novel mutations were identified. A wide range in age of onset (0-72 years) and loss of ambulation (5-74 years) was found. Fifteen patients (6%) initially presented with asymptomatic hyperCKemia. Cardiac abnormalities were found in 35 patients (17%). Non-invasive ventilation was started in 34 patients (14%). Both cardiac and respiratory involvement occurs across all subtypes, stressing the need for screening in all included subtypes.     

Analysis of DYSF gene mutations in two pedigrees affected with limb-girdle muscular dystrophy type 2BCSCD

Objective: To analyze mutations of DYSF gene in two pedigrees affected with limb-girdle muscular dystrophy 2B (LGMD-2B). Methods: Genomic DNA was extracted from peripheral blood samples of the two probands and unaffected family members. Variant sites were screened by next-generation sequencing using gene panel as well as Sanger sequencing. Results: Four pathogenic mutations of the DYSF gene were detected, which included a de novo mutation and three mutations with uncertain significance. In pedigree 1, the proband carried compound heterozygous mutations of c. 1667T>C (p. Leu556Pro) and c. 5567T>A (p. Vall856Glu), which were respectively inherited from her mother and father. Proband of pedigree 2 carried compound heterozygous mutations of c. 4853A>G (p. Tyrl618Cys) and c. 4876G> A (p. Vall612Ile), among which c. 4876G> A (p. Vall626Ile) was also found in his father and grandfather, while c. 4853A>G (p. Tyrl618Cys) was detected in his mother and grandmother. Conclusion: The two compound heterozygous mutations of the DYSF gene probably underlie the LGMD2B in the two pedigrees. Next generation sequencing has conferred great advantage for gene diagnosis of hereditary myopathy. © 2018 MeDitorial Ltd. All rights reserved.     

一个常染色体显性遗传Emery-Dreifuss型肌营养不良家系的基因突变分析

目的 探讨一个常染色体显性遗传Emery-Dreifuss型肌营养不良(Emery-Dreifuss muscular dystrophy,EDMD)家系的临床、病理及遗传学特点.方法 收集家系中2例患者(先证者及女儿)的临床资料及骨骼肌标本,行组织化学染色病理分析;收集先证者及家系成员(3代7人)血液DNA标本,采用聚合酶链反应和DNA直接测序方法 对LMNA基因进行突变检测;明确基因变异位点后对家系行单倍型分析.结果 先证者具有典型的EDMD临床表现:关节挛缩、进行性加重的肌无力和肌萎缩、心脏传导异常;骨骼肌活检病理示肌源性合并轻度神经源性改变;2例患者LMNA基因第9外显子发现杂合错义突变1583(C→G)(T528R),表型正常的其他家系成员未发现该突变;单倍型分析显示先证者及女儿具有相同的致病单倍型.结论 报道了中国人常染色体显性遗传EDMD患者的表现型及基因型.     

Dysferlin缺陷:肢带2B型肌营养不良与Miyoshi肌病的致病原因

目的　对临床怀疑为常染色体隐性遗传性肌营养不良一家系进行分析 ,以明确肌病类型并寻找其致病基因的分子缺陷。方法　用与 8种常染色体隐性遗传性肌营养不良基因连锁的短串联重复序列标记进行连锁分析 ,用与 5种肌营养不良相关的单克隆抗体作多重免疫印迹分析检测相应致病基因的编码产物 ;通过逆转录 - PCR扩增先证者致病基因的编码序列并测序 ,确定基因突变。结果　家系连锁分析显示在 DYSF基因附近的 D2 S337位点的优势对数记分值为 1.85 ,提示致病基因与 D2 S337连锁 ;免疫印迹分析提示患者DYSF基因的编码产物 dysferlin缺陷 ;测序证明先证者DYSF基因的c DNA第 6 4 2 9位发生纯合性del G突变。结论　综合研究结果和临床资料 ,这一家系中的先证者被诊断为 Miyoshi肌病 ,由DYSF基因纯合性缺失突变所导致。     

Myotonic dystrophy and limb girdle muscular dystrophy in one family

A family is reported in which a 29-year-old woman showed the clinical features of myotonic dystrophy while her 26-year-old brother presented with the clinical picture of limb girdle syndrome. In the affected female, direct genetic testing for the specific myotonic dystrophy mutation on chromosome 19 revealed abnormal expansion of a repeat unit containing the three nucleotides cytosine, thymine, and guanine (CTG) — typical for myotonic dystrophy — while her diseased brother displayed two normal alleles. This supports the hypothesis of the extremely rare occurrence of two clinically and genetically different myopathies in one family. Genetic analysis of six other family members showed that the father of the diseased siblings as well as all of his three brothers and sisters had a pathological CTG repeat expansion, and that the other two family members tested had a normal allelic pattern. The number of CTG repeats in the diseased women was approximately tenfold higher than in her asymptomatic relatives who revealed an abnormal allelic pattern. The increase in CTG repeats with transmission to a subsequent generation in this family was paralleled by a dramatic increase in the severity of myotonic dystrophy.Abbreviations DM myotonic dystrophy - LGS limb girdle syndrome - LGMD limb girdle muscular dystrophy - CTG cytosine, thymine, guanine - PCR polymerase chain reaction     

中国人肢带型肌营养不良症粘附蛋白基因突变鉴定

目的肢带型肌营养不良症（ＬＧＭＤ）是常见的常染色体遗传肌肉病，特点为髋肩带肌无力、萎缩，进行性发展至远端肌肉，男女均可受累，有明显的遗传异质性，国外研究发现重型ＬＧＭＤ分别涉及１３ｑ１２、１７ｑ２１、４ｑ１２、５ｑ３３区域编码γ－、α－、β－、δ－糖蛋白的４个基因座位。中国人群中ＬＧＭＤ的致病基因研究尚无报道，拟通过粘附蛋白（ａｄｈａｌｉｎ）基因突变的检测，鉴定其致病基因。方法用ＰＣＲ－ＳＳＣＰ及ＤＮＡ测序法对ａｄｈａｌｉｎ基因第２、３外显子进行了突变检测及鉴定。结果发现１例散发的９岁女患者ａｄｈａｌｉｎ第２、３外显子存在纯合Ａｒｇ７７Ｃｙｓ突变，此突变在本实验的４０条野生染色体中未发现。结论发现中国人群中重型ＬＧＭＤ（ＤＬＭＤ）存在ａｄｈａｌｉｎ基因突变。提示１７ｑ２１区的ａｄｈａｌｉｎ基因是中国人ＬＧＭＤ的一个致病基因。     

How to tackle the diagnosis of limb-girdle muscular dystrophy 2A

Limb-girdle muscular dystrophy (LGMD) 2A (calpainopathy) is the most frequent form of LGMD in many European countries. The increasing demand for a molecular diagnosis makes the identification of strategies to improve gene mutation detection crucial. We conducted both a quantitative analysis of calpain-3 protein in 519 muscles from patients with unclassified LGMD, unclassified myopathy and hyperCKemia, and a functional assay of calpain-3 autolytic activity in 108 cases with LGMD and normal protein quantity. Subsequently, screening of CAPN3 gene mutations was performed using allele-specific tests and simplified SSCP analysis. We diagnosed a total of 94 LGMD2A patients, carrying 66 different mutations (six are newly identified). The probability of diagnosing calpainopathy was very high in patients showing either a quantitative (80%) or a functional calpain-3 protein defect (88%). Our data show a high predictive value for reduced-absent calpain-3 or lost autolytic activity. These biochemical assays are powerful tools for otherwise laborious genetic screening of cases with a high probability of being primary calpainopathy. Our multistep diagnostic approach is rational and highly effective. This strategy has improved the detection rate of the disease and our extension of screening to presymptomatic phenotypes (hyperCKemia) has allowed us to obtain early diagnoses, which has important consequences for patient care and genetic counseling.     

Intrafamilial variability of limb-girdle muscular dystrophy,LGMD1D type

LGMD1D is an autosomal dominant limb girdle muscular dystrophy caused by variants in the DNAJB6 gene. This is typically an adult-onset disorder characterized by moderately progressive proximal muscle weakness without respiratory or bulbar involvement; however phenotypic variability is often observed with some individuals having earlier onset and more severe symptoms. Here, we present a family with a novel NM_005494.2:c.271T > G p.(Phe91Val) variant in DNAJB6 with a late-onset, mild and slowly progressive form of the disease, including one individual, who in her 7th decade of life has subclinical LGMD1D with only mild features on muscle biopsy and MRI. Unlike previously reported cases where missense variants affecting the Phe91 amino acid residue are associated with a more severe form of the disease, this family represents the mild end of the LGMD1D clinical spectrum. Therefore, this family adds further complexity to the genotype-phenotype correlation in DNAJB6-associated muscular dystrophies.     

Germinal mosaicism in a Duchenne muscular dystrophy family: implications for genetic counselling

Melis MA, Cau M. Congiu R, Puddu R, Muntoni F, Cao A. Germinal mosaicism in a Duchenne muscular dystrophy family: implications for genetic counselling.
Clin Genet 1993: 43: 247–249. © Munksgaard, 1993
In this study we describe a three-generation family in which two siblings were affected by Duchenne muscular dystrophy (DMD). Immunohisto-chemical analysis of muscle dystrophin and haplotype analysis of the DMD locus revealed that the X chromosome carrying the DMD gene was transmitted from the healthy maternal grandfather to his three daughters. including the proband's mother. These findings indicate that the grandfather was a germinal mosaic for the DMD gene. The definition of the carrier status in two possible carriers led us to give accurate genetic counselling and to prevent the birth of an affected boy. The results of this study demonstrate the usefulness of haplotype analysis and immuno-histochemical muscle dystrophin studies to detect hidden germinal mosaicism and to improve genetic counselling.     

Diagnosis and cell-based therapy for Duchenne muscular dystrophy in humans,mice, and zebrafish

The muscular dystrophies are a heterogeneous group of genetically caused muscle degenerative disorders. The Kunkel laboratory has had a longstanding research program into the pathogenesis and treatment of these diseases. Starting with our identification of dystrophin as the defective protein in Duchenne muscular dystrophy (DMD), we have continued our work on normal dystrophin function and how it is altered in muscular dystrophy. Our work has led to the identification of the defective genes in three forms of limb girdle muscular dystrophy (LGMD) and a better understanding of how muscle degenerates in many of the different dystrophies. The identification of mutations causing human forms of dystrophy has lead to improved diagnosis for patients with the disease. We are continuing to improve the molecular diagnosis of the dystrophies and have developed a high-throughput sequencing approach for the low-cost rapid diagnosis of all known forms of dystrophy. In addition, we are continuing to work on therapies using available animal models. Currently, there are a number of mouse models of the human dystrophies, the most notable being the mdx mouse with dystrophin deficiency. These mice are being used to test possible therapies, including stem-cell-based approaches. We have been able to systemically deliver human dystrophin to these mice via the arterial circulation and convert 8% of dystrophin-deficient fibers to fibers expressing human dystrophin. We are now expanding our research to identify new forms of LGMD by analyzing zebrafish models of muscular dystrophy. Currently, we have 14 different zebrafish mutants exhibiting various phenotypes of muscular dystrophy, including muscle weakness and inactivity. One of these mutants carries a stop codon mutation in dystrophin, and we have recently identified another carrying a mutation in titin. We are currently positionally cloning the disease-causative mutation in the remaining 12 mutant strains. We hope that one of these new mutant strains of fish will have a mutation in a gene not previously implicated in human muscular dystrophy. This gene would become a candidate gene to be analyzed in patients which do not carry a mutation in any of the known dystrophy-associated genes. By studying both disease pathology and investigating potential therapies, we hope to make a positive difference in the lives of people living with muscular dystrophy.     

The most common mutation in FKRP causing limb girdle muscular dystrophy type 2I (LGMD2I) may have occurred only once and is present in Hutterites and other populations

Limb girdle muscular dystrophy (LGMD) is common in the Hutterite population of North America. We previously identified a mutation in the TRIM32 gene in chromosome region 9q32, causing LGMD2H in approximately two-thirds of the 60 Hutterite LGMD patients studied to date. A genomewide scan was undertaken in five families who did not show linkage to the LGMD2H locus on chromosome 9. A second LGMD locus, LGMD2I, was identified in chromosome region 19q13.3, and the causative mutation was identified as c.826C>A (L276I), a missense mutation in the FKRP gene. A comparison of the clinical characteristics of the two LGMD patient groups in this population reveals some differences. LGMD2I patients generally have an earlier age at diagnosis, a more severe course, and higher serum creatine kinase (CK) levels. In addition, some of these patients show calf hypertrophy, cardiac symptoms, and severe reactions to general anesthesia. None of these features are present among LGMD2H patients. A single common haplotype surrounding the FKRP gene was identified in the Hutterite LGMD2I patients. An identical core haplotype was also identified in 19 other non-Hutterite LGMD2I patients from Europe, Canada, and Brazil. The occurrence of this mutation on a common core haplotype suggests that L276I is a founder mutation that is dispersed among populations of European origin.     

Clinicogenetic lessons from 370 patients with autosomal recessive limb-girdle muscular dystrophy

Limb-girdle muscular dystrophies (LGMD) are a group of genetically heterogeneous disorders characterized by predominantly proximal muscle weakness. We aimed to characterize epidemiological, clinical and molecular data of patients with autosomal recessive LGMD2/LGMD-R in Brazil. A multicenter historical cohort study was performed at 13 centers, in which index cases and their affected relatives' data from consecutive families with genetic or pathological diagnosis of LGMD2/LGMD-R were reviewed from July 2017 to August 2018. Survival curves to major handicap for LGMD2A/LGMD-R1-calpain3-related, LGMD2B/LGMD-R2-dysferlin-related and sarcoglycanopathies were built and progressions according to sex and genotype were estimated. In 370 patients (305 families) with LGMD2/LGMD-R, most frequent subtypes were LGMD2A/LGMD-R1-calpain3-related and LGMD2B/LGMD-R2-dysferlin-related, each representing around 30% of families. Sarcoglycanopathies were the most frequent childhood-onset subtype, representing 21% of families. Five percent of families had LGMD2G/LGMD-R7-telethonin-related, an ultra-rare subtype worldwide. Females with LGMD2B/LGMD-R2-dysferlin-related had less severe progression to handicap than males and LGMD2A/LGMD-R1-calpain3-related patients with truncating variants had earlier disease onset and more severe progression to handicap than patients without truncating variants. We have provided paramount epidemiological data of LGMD2/LGMD-R in Brazil that might help on differential diagnosis, better patient care and guiding future collaborative clinical trials and natural history studies in the field.     

LIMS2 mutations are associated with a novel muscular dystrophy,severe cardiomyopathy and triangular tongues

Limb girdle muscular dystrophy (LGMD) is a heterogeneous group of genetic disorders leading to progressive muscle degeneration and often associated with cardiac complications. We present two adult siblings with childhood‐onset of weakness progressing to a severe quadriparesis with the additional features of triangular tongues and biventricular cardiac dysfunction. Whole exome sequencing identified compound heterozygous missense mutations that are predicted to be pathogenic in LIMS2. Biopsy of skeletal muscle demonstrated disrupted immunostaining of LIMS2. This is the first report of mutations in LIMS2 and resulting disruption of the integrin linked kinase (ILK)–LIMS–parvin complex associated with LGMD.