Dominant Myopathy Research Articles

Calcium Influx Analysis by TIRF Microscopy on Cultured Primary Myotubes from Patients with RyR1 Mutations

Central core disease (CCD) and malignant hyperthermia (MH) have been linked to point mutations in the gene encoding the skeletal muscle sarcoplasmic reticulum calcium release channel (ryanodine receptor), which is localized on human chromosome 19 (RYR11). Central core disease is a relatively mild, slowly progressive autosomal dominant myopathy, characterized histologically by the presence of centrally located cores running the length of the muscle fibres. MH is a pharmacogenetic induced hypermetabolic disease.

Autosomal dominant nemaline myopathy caused by a novel α-tropomyosin 3 mutation

Nemaline myopathy (NM) is a genetically and clinically heterogenous muscle disorder, which is myopathologically characterized by nemaline bodies. Mutations in six genes have been reported to cause NM: Nebulin (NEB Pelin 1999), alpha-skeletal muscle actin (ACTA1 Nowak 1999), alpha-slow tropomyosin (TPM3 Laing 1995), beta-tropomyosin (TPM2 Donner 2002), slow troponin T (TNNT1 Johnston 2000) and cofilin 2 (CFL2 Agrawal 2007). The majority of cases are due to mutation in NEB and ACTA1. We report on the clinical, myopathological and muscle MRI findings in a German family with autosomal dominant NM due to a novel pathogenic TPM3 mutation (p.Ala156Thr).

Centronuclear myopathy with cataracts due to a novel dynamin 2 ( DNM2) mutation

Dynamin 2 ( DNM2)-related dominant centronuclear myopathy is usually a mild disorder, but more severe variants have been associated with mutations affecting the pleckstrin homology (PH) domain of the protein, mainly implicated in different forms of Charcot–Marie–Tooth Disease (CMT). Whilst DNM2-related CMT may feature non-neurological findings including cataracts, this has not been reported in DNM2-related centronuclear myopathy. We report a girl presenting from birth with hypotonia, respiratory and feeding difficulties. Motor development was delayed and at 9 years she lost the ability to walk. She had ptosis, external ophthalmoplegia and bilateral cataracts. Muscle biopsy showed increase in central nuclei with type 1 hypotrophy and fibrosis. DNM2 screening revealed a novel heterozygous substitution (c.1862T>C; p.Leu621Pro) affecting the PH domain of the protein. Her further course was progressive and at 14 years she died from respiratory failure. Our findings expand the phenotypical spectrum associated with DNM2 mutations and provide a new clinical indicator for involvement of this gene in patients with centronuclear myopathy.

Adult course in dynamin 2 dominant centronuclear myopathy with neonatal onset

We report a family with autosomal dominant centronuclear (myotubular) myopathy caused by a novel mutation, p.A618D, in dynamin 2 ( DNM2). The 64-year-old mother and 26-year-old daughter had neonatal onset with hypotonia and weak suckling, followed by improvement, then slowly progressive muscle weakness and respiratory restriction. Muscle biopsy showed radial sarcoplasmic strands around the frequent central nuclei. Electrophysiology revealed predominantly myopathic patterns without peripheral nerve involvement. Centronuclear myopathy with neonatal onset caused by a DNM2 mutation in the C-terminal part of the pleckstrin homology domain may have a favorable prognosis and follow a course similar to adult-onset centronuclear myopathy. We advise respiratory follow-up in these patients.

The first Italian family with tibial muscular dystrophy caused by a novel titin mutation

Tibial muscular dystrophy (TMD) or Udd myopathy is an autosomal dominant distal myopathy with late onset, at first described in the Finnish population. We report here the first Italian cases of TTN mutated titinopathy. The proband, a 60 year-old female, had the first muscular signs at the age of 59 years, with difficulty in walking and right foot drop. Muscle imaging showed selective fatty degenerative change in the anterior compartment of leg muscles. Her 67 year-old brother, started to show muscle weakness, pain at lower limbs and hypertrophy of calf muscles at the age of 66 years. Their mother began to show foot drop and impaired walking from the age of 60 years. Other relatives are reported to be affected in a similar way. Because the phenotype appeared compatible with TMD, we analyzed the TTN gene in the DNA of the proband and we identified a heterozygous mutation 293326A>C. This mutation is also present in the brother and in the other affected individuals of the same family. The mutation predicts a His33378Pro change located next to the previously known Belgian TMD mutation. The mutation was not found in 100 Italian control DNA samples. Then, since the introduction of a proline in the last domain of titin was previously known to cause TMD in French families, we can conclude that this missense mutation is the obvious pathogenetic mutation in the affected patients. No other disease causing mutations in the TTN gene have so far been reported in the Italian population.

First genomic rearrangement of the RYR1 gene associated with an atypical presentation of lethal neonatal hypotonia

Neonatal hypotonia is frequently observed with a highly variable clinical presentation. Congenital myopathies that are classically characterized by the presence of structural changes of the muscle fibres such as cores, rods and aggregates have been reported to be occasionally associated with this presentation. However, the identification of the causing defect can be a challenging task in severe neonatal forms of the disease since specific structural changes might not always be present in affected newborn’s muscles. The RYR1 gene encodes the skeletal muscle isoform of a calcium channel, the ryanodine receptor, and has been involved in both dominant and recessive congenital myopathies associated with structural changes and presenting with various degree of severity. Here we report the case of a child presenting at birth with a lethal form of neonatal hypotonia associated with an atypical congenital myopathy. Molecular investigations showed that the disease was caused by two novel RYR1 mutations. One of the mutations was a large-sized genomic deletion. This is the first genomic rearrangement identified into the RYR1 gene to our knowledge. This new class of mutation of the RYR1 gene will clearly have consequences for the molecular investigation of RYR1-related diseases.

Autosomal dominant distal vacuolar myopathy associated with mutation of the nuclear matrix protein matrin 3

Inherited distal myopathies represent a heterogeneous group of skeletal muscle disorders. One type of adult-onset, progressive autosomal dominant distal myopathy, frequently associated with dysphagia and dysphonia, has been mapped to chromosome 5q31 in a North American pedigree (vocal cord and pharyngeal weakness with distal myopathy; VCPDM). We recently identified a second large VCPDM family of Bulgarian descent and performed fine mapping of the critical interval. Sequencing of positional candidate genes revealed precisely the same non-conservative S85C missense mutation affecting an interspecies conserved residue in the MATR3 gene in both families (Senderek et al., Am J Human Genet, in press). MATR3 is expressed in skeletal muscle and encodes matrin 3, a component of the proteinaceous network that extends throughout the nucleus and has been termed the nuclear matrix. Different disease related haplotype signatures in the two families provide evidence that two independent mutational events at the same position in MATR3 cause VCPDM. Histopathological and electron microscopical analysis of two muscle biopsies revealed reduced matrin 3 immunoreactivity of muscle fiber nuclei and myonuclear degeneration as well as autophagic vacuoles in affected muscle fibers.

O7-4 Kelch-like homolog 9 (KLHL9) mutation is associated with an early onset autosomal dominant distal myopathy

O7-4 Kelch-like homolog 9 (KLHL9) mutation is associated with an early onset autosomal dominant distal myopathy

G.O.5 A new autosomal dominant distal vacuolar myopathy associated with mutation of the nuclear matrix protein, matrin 3

Distal myopathies represent a heterogeneous group of inherited skeletal muscle disorders. One type of adult-onset, progressive autosomal dominant distal myopathy, frequently associated with dysphagia and dysphonia, has been mapped to chromosome 5q31 in a North American pedigree (vocal cord and pharyngeal weakness with distal myopathy; VCPDM). We report the identification of a second large VCPDM family of Bulgarian descent and fine mapping of the critical interval. Sequencing of positional candidate genes revealed precisely the same non-conservative S85C missense mutation affecting an interspecies conserved residue in the MATR3 gene in both families.

Dynamin 2 mutations associated with human diseases impair clathrin-mediated receptor endocytosis

Dynamin 2 (DNM2) is a large GTPase involved in the release of nascent vesicles during endocytosis and intracellular membrane trafficking. Distinct DNM2 mutations, affecting the middle domain (MD) and the Pleckstrin homology domain (PH), have been identified in autosomal dominant centronuclear myopathy (CNM) and in the intermediate and axonal forms of the Charcot-Marie-Tooth peripheral neuropathy (CMT). We report here the first CNM mutation (c.1948G>A, p.E650 K) in the DNM2 GTPase effector domain (GED), leading to a slowly progressive moderate myopathy. COS7 cells transfected with DNM2 constructs harboring a disease-associated mutation in MD, PH, or GED show a reduced uptake of transferrin and low-density lipoprotein (LDL) complex, two markers of clathrin-mediated receptor endocytosis. A decrease in clathrin-mediated endocytosis was also identified in skin fibroblasts from one CNM patient. We studied the impact of DNM2 mutant overexpression on epidermal growth factor (EGF)-induced extracellular signal-regulated kinase 1 (ERK1) and ERK2 activation, known to be an endocytosis- and DNM2-dependent process. Activation of ERK1/2 was impaired for all the transfected mutants in COS7 cells, but not in CNM fibroblasts. Our results indicate that impairment of clathrin-mediated endocytosis may play a role in the pathophysiological mechanisms leading to DNM2-related diseases, but the tissue-specific impact of DNM2 mutations in both diseases remains unclear.

Three-generation Familial Visceral Myopathy With α-actin–positive Inclusion Bodies in Intestinal Smooth Muscle

We report the clinical and histopathologic findings of a family with 7 affected members in 3 generations suffering from autosomal dominant visceral myopathy. All patients presented with chronic intestinal pseudo-obstruction affecting especially the entire small bowel. Histologic abnormalities involved intestinal smooth muscle, with degeneration and fibrosis of the muscularis propria. In addition, the inner circular layer of the muscularis propria contained alpha-smooth muscle actin-positive and, in more advanced disease, also periodic acid-Schiff-positive inclusion bodies. The inclusions were invisible in routine hematoxylin-eosin-stained sections, but were visible in immunohistochemical stainings for alpha-smooth muscle actin. No abnormality was evident in muscularis mucosae or in blood vessels, and the findings remained unidentified in mucosal biopsy specimens. To our knowledge, this is the first reported alpha-actin-positive inclusion body finding in familial visceral myopathy.

Inclusion body myopathy with Paget disease and frontotemporal dementia (IBMPFD): clinical features including sphincter disturbance in a large pedigree

Autosomal dominant inclusion body myopathy (IBM) associated with Paget disease of bone (PDB) and frontotemporal dementia (FTD), or IBMPFD, is a rare recently described multisystem disorder caused by missense mutations...

Phenotypic variability in a Spanish family with a Caveolin-3 mutation

We report a Spanish family affected from a late onset, hand-involved and autosomal dominant distal myopathy associated to Caveolin-3 mutation. Signs of muscle hyperexcitability and hyperckemia were observed in the youngest relatives but not motor symptoms. Patients and methods Neurological examination was performed in all members of the family. Muscle biopsy sample was taken from the proband and DNA genomics was amplified for the two exons of Cav-3 by the polymerase chain reaction (PCR) in all the affected members and in three asymptomatic relatives. Results Signs of muscle hyperexcitability and hyperckemia were observed in the affected members from early ages. Cav-3 expression was greatly reduced in the sarcolemma of the proband's muscle. Genetic studies revealed a G → A transition at nucleotide position 80 in exon 1 of the Cav-3 gene (c.80G > A), generating a Arg → Gln change at codon 27 (p.R27Q) of the amino acid chain in heterozygous state, while no mutation was found in unaffected members. Conclusions Signs of muscle hyperexcitability and hyperckemia at early ages may predict the development of a late onset autosomal dominant hand-involved myopathy associated to Cav-3 mutation in the family reported herein.

A novel mutation in the dynamin 2 gene in a Charcot-Marie-Tooth type 2 patient: Clinical and pathological findings

Mutations in dynamin 2 (DNM2) have been associated with autosomal dominant centronuclear myopathy, dominant intermediate Charcot-Marie-Tooth (CMT) type B and CMT2. Here, we report a novel DNM2 mutation in the Pleckstrin homology domain of DNM2 (p.K559del) in a patient with an axonal length-dependent sensorimotor polyneuropathy predominantly affecting the lower limbs. Neuropathy is associated with congenital cataracts, ophthalmoparesis, ptosis and neutropenia. There was no evidence of a skeletal myopathy on EMG or muscle biopsy. We suggest that this constellation of clinical features can help the diagnosis and selection of patients for direct DNM2 genetic analysis.

Myofibrillar myopathy with arrhythmogenic right ventricular cardiomyopathy 7: corroboration and narrowing of the critical region on 10q22.3

Several years ago, autosomal dominant myofibrillar myopathy (MFM) in combination with arrhythmogenic right ventricular cardiomyopathy (ARVC7) was tentatively mapped to a 10.6-Mbp (million base pairs) region on chromosome 10q22.3 between D10S605 (78.9 Mbp) and D10S215 (89.5 Mbp) in a Swedish family assuming that ARVC7 was allelic with cardiomyopathy, dilated 1C (CMD1C). To date, neither the genetic defect in ARVC7 nor CMD1C has been reported. In a comprehensive follow-up study we re-examined and confirmed the previous linkage data for ARVC7 using a high-density single nucleotide polymorphism marker panel from Affymetrix (Human Mapping 10K Array). No other regions with significant evidence for linkage were discovered. The critical interval was narrowed down to 4.27 Mbp between D10S1645 and D10S1786. This reduced the total number of candidate genes to 18 of which 17 (RAI17, PPIF, C10ORF56, SFTPA1, SFTPA2, SFTPA1B, SFTPA2B, SFTPD, C10ORF57, PLAC9, ANXA11, MAT1A, DYDC1, DYDC2, C10ORF58, TSPAN14 and SH2D4B) are shared with the CMD1C region. No disease-causing mutation was found in their coding regions. Moreover, metavinculin (VCL) and ZASP/cypher (LDB3) proximal and distal to this linked region were excluded by sequence analysis. To search for submicroscopic and intragenic deletions by PCR, we generated hybrid cell lines carrying only the affected or normal chromosome 10 homolog. All sequence tagged sites and exons were present on both homologs. We speculate that regulatory mutations in 1 of the 18 genes from 10q22.3 are responsible for a heterogenous spectrum of clinically distinct myodegenerative disorders, affecting both skeletal and cardiac muscles to variable degrees.

X-Linked Dominant Scapuloperoneal Myopathy Is Due to a Mutation in the Gene Encoding Four-and-a-Half-LIM Protein 1

Scapuloperoneal (SP) syndrome encompasses heterogeneous neuromuscular disorders characterized by weakness in the shoulder-girdle and peroneal muscles. In a large Italian-American pedigree with dominant SP myopathy (SPM) previously linked to chromosome 12q, we have mapped the disease to Xq26, and, in all of the affected individuals, we identified a missense change (c.365G-->C) in the FHL1 gene encoding four-and-a-half-LIM protein 1 (FHL1). The mutation substitutes a serine for a conserved trypophan at amino acid 122 in the second LIM domain of the protein. Western blot analyses of muscle extracts revealed FHL1 loss that paralleled disease severity. FHL1 and an isoform, FHL1C, are highly expressed in skeletal muscle and may contribute to stability of sarcomeres and sarcolemma, myofibrillary assembly, and transcriptional regulation. This is the first report, to our knowledge, of X-linked dominant SP myopathy and the first human mutation in FHL1.

Congenital myopathies

The aim of this review is to provide an up-to-date personal analysis of current congenital myopathy research.In the past year novel congenital myopathies have been suggested, genes have been discovered for some of the congenital myopathies for the first time (beta-tropomyosin in cap disease and perhaps skeletal muscle alpha-actin in Zebra body myopathy), further genes have been identified for congenital myopathies where other genes had already been found (cofilin in nemaline myopathy, selenoprotein N in congenital fibre type disproportion) and recessive myosin storage myopathy was associated with homozygous mutation of slow-skeletal/beta-cardiac myosin which was already known to be mutated in dominant myosin storage myopathy. There has been further clarification of the pathobiology of the congenital myopathies, including determination of the basis of epigenetic effects: silencing of the normal allele in recessive central core disease and persistence of cardiac (fetal) alpha-actin in nemaline myopathy patients with no skeletal actin.The increased understanding of the genes and pathobiology of the congenital myopathies that is developing should ultimately lead to effective treatments.

C.P.4.13 A RYR1-linked dominant core myopathy presenting with predominant distal involvement (foot drop): Clinical and morphological variability

Core myopathies (CCD, MmD) are defined by the presence of areas of sarcomere disorganization and mitochondria depletion of variable size and length (short in MmD, spanning the whole fiber length in CCD). Most dominant or recessive CCD cases are due to mutations of RYR1, while in the autosomal recessive MmD mutations in RYR1 or SEPN1 genes have been reported. Furthermore, the spectrum of clinical manifestations of core myopathies might be larger than classically described. The aim of this study was to report on unusual clinical and pathomorphological features of a family with a dominant core myopathy linked to the RYR1 locus.

C.P.1.13 A homozygous null mutation in TPM2 gene causes autosomal recessive nemaline myopathy associated with multiple pterygia

Tropomyosins (TM) are a family of highly conserved actin-binding proteins composed of two subunits that form a coiled-coil structure. Skeletal muscle contains two forms of tropomyosin (alpha and beta subunits) localized to the thin filaments where they regulate Ca2+-dependant muscle contraction in association with the troponin complex. The beta subunit is encoded by the TPM2 gene composed of 9 exons of which four are alternatively spliced (exons 1, 2, 6 and 9). Mutations in TPM2 gene have been associated so far with two allelic neuromuscular disorders, autosomal dominant nemaline myopathy (NEM) and distal arthrogryposis (DA). We report an Algerian consanguineous family in which a male child presented at birth with severe hypotonia, distal amyotrophy, arthrogryposis and multiple pterygia, facial dysmorphia, ptosis and ophtalmoplegia. Three first cousins were also affected. Nemaline myopathy was diagnosed on muscle biopsy. After exclusion of ACTA1, TPM3 and NEB genes by linkage studies, a null mutation was identified at a homozygous level in all affected family members. The mutation is localized in exon 6b, specific of the skeletal muscle isoform. A low amount of transcript was detected by quantitative RT-PCR and absence of TPM2 expression in the muscle was confirmed by Western blot analysis. Identification of a null allele mutation in the TNNT1 gene has been reported in the Amish population in association with a lethal form of autosomal recessive nemaline myopathy. By contrast, the null mutation identified in the family is not life-threatening thus indicating a possible mechanism of compensation for total absence of TPM2.

G.P.7.13 Gene expression profiling in a skeletal muscle cell model of oculopharyngeal muscular dystrophy reveals an extracellular matrix defect

Oculopharyngeal muscular dystrophy (OPMD) is a late-onset, usually autosomal dominant myopathy. OPMD is caused by a small expansion of an alanine (Ala) tract at the N-terminus of the nuclear poly(A)-binding protein (PABPN1) and is clinically characterised by progressive ptosis, dysphagia and limb muscle weakness. The pathological hallmark is the accumulation of unique tubulofilamentous inclusions (INI) within the nuclei of skeletal muscle fibers. These inclusions contain PABPN1 and also sequester ubiquitin, proteasome subunits and heat shock proteins as well as poly(A) RNA.