Objective
Mutations in the genes encoding the extracellular matrix protein collagen VI (ColVI) cause a spectrum of disorders with variable inheritance including Ullrich congenital muscular dystrophy, ...Bethlem myopathy, and intermediate phenotypes. We extensively characterized, at the clinical, cellular, and molecular levels, 49 patients with onset in the first 2 years of life to investigate genotype‐phenotype correlations.
Methods
Patients were classified into 3 groups: early‐severe (18%), moderate‐progressive (53%), and mild (29%). ColVI secretion was analyzed in patient‐derived skin fibroblasts. Chain‐specific transcript levels were quantified by quantitative reverse transcriptase polymerase chain reaction (qRT‐PCR), and mutation identification was performed by sequencing of complementary DNA.
Results
ColVI secretion was altered in all fibroblast cultures studied. We identified 56 mutations, mostly novel and private. Dominant de novo mutations were detected in 61% of the cases. Importantly, mutations causing premature termination codons (PTCs) or in‐frame insertions strikingly destabilized the corresponding transcripts. Homozygous PTC‐causing mutations in the triple helix domains led to the most severe phenotypes (ambulation never achieved), whereas dominant de novo in‐frame exon skipping and glycine missense mutations were identified in patients of the moderate‐progressive group (loss of ambulation).
Interpretation
This work emphasizes that the diagnosis of early onset ColVI myopathies is arduous and time‐consuming, and demonstrates that quantitative RT‐PCR is a helpful tool for the identification of some mutation‐bearing genes. Moreover, the clinical classification proposed allowed genotype‐phenotype relationships to be explored, and may be useful in the design of future clinical trials. ANN NEUROL 2010;68:511–520
Centronuclear myopathies are congenital muscle disorders characterized by type I myofibre predominance and an increased number of muscle fibres with nuclear centralization. The severe neonatal ...X-linked form is due to mutations in MTM1, autosomal recessive centronuclear myopathy with neonatal or childhood onset results from mutations in BIN1 (amphiphysin 2), and dominant cases were previously associated to mutations in DNM2 (dynamin 2). Our aim was to determine the genetic basis and physiopathology of patients with mild dominant centronuclear myopathy without mutations in DNM2. We hence established and characterized a homogeneous cohort of nine patients from five families with a progressive adult-onset centronuclear myopathy without facial weakness, including three sporadic cases and two families with dominant disease inheritance. All patients had similar histological and ultrastructural features involving type I fibre predominance and hypotrophy, as well as prominent nuclear centralization and clustering. We identified heterozygous BIN1 mutations in all patients and the molecular diagnosis was complemented by functional analyses. Two mutations in the N-terminal amphipathic helix strongly decreased the membrane-deforming properties of amphiphysin 2 and three stop-loss mutations resulted in a stable protein containing 52 supernumerary amino acids. Immunolabelling experiments revealed abnormal central accumulation of dynamin 2, caveolin-3, and the autophagic marker p62, and general membrane alterations of the triad, the sarcolemma, and the basal lamina as potential pathological mechanisms. In conclusion, we identified BIN1 as the second gene for dominant centronuclear myopathy. Our data provide the evidence that specific BIN1 mutations can cause either recessive or dominant centronuclear myopathy and that both disorders involve different pathomechanisms.
Nemaline myopathy (NM) is a muscle disorder with broad clinical and genetic heterogeneity. The clinical presentation of affected individuals ranges from severe perinatal muscle weakness to milder ...childhood-onset forms, and the disease course and prognosis depends on the gene and mutation type. To date, 14 causative genes have been identified, and ACTA1 accounts for more than half of the severe NM cases. ACTA1 encodes alpha-actin, one of the principal components of the contractile units in skeletal muscle. We established a homogenous cohort of ten unreported families with severe NM, and we provide clinical, genetic, histological, and ultrastructural data. The patients manifested antenatal or neonatal muscle weakness requiring permanent respiratory assistance, and most deceased within the first months of life. DNA sequencing identified known or novel ACTA1 mutations in all. Morphological analyses of the muscle biopsy specimens showed characteristic features of NM histopathology including cytoplasmic and intranuclear rods, cytoplasmic bodies, and major myofibrillar disorganization. We also detected structural anomalies of the perinuclear space, emphasizing a physiological contribution of skeletal muscle alpha-actin to nuclear shape. In-depth investigations of the nuclei confirmed an abnormal localization of lamin A/C, Nesprin-1, and Nesprin-2, forming the main constituents of the nuclear lamina and the LINC complex and ensuring nuclear envelope integrity. To validate the relevance of our findings, we examined muscle samples from three previously reported ACTA1 cases, and we identified the same set of structural aberrations. Moreover, we measured an increased expression of cardiac alpha-actin in the muscle samples from the patients with longer lifespan, indicating a potential compensatory effect. Overall, this study expands the genetic and morphological spectrum of severe ACTA1-related nemaline myopathy, improves molecular diagnosis, highlights the enlargement of the perinuclear space as an ultrastructural hallmark, and indicates a potential genotype/phenotype correlation. Keywords: ACTA1, Congenital myopathy, Nemaline rods, Intranuclear rods, Cytoplasmic bodies, Nuclear envelope, Neuromuscular junction
Autosomal dominant limb girdle muscular dystrophy D3 HNRNPDL-related is a rare dominant myopathy caused by mutations in
HNRNPDL
. Only three unrelated families have been described worldwide, a ...Brazilian and a Chinese carrying the mutation c.1132G>A p.(Asp378Asn), and one Uruguayan with the mutation c.1132G>C p. (Asp378His), both mutations occurring in the same codon. The present study enlarges the clinical, morphological and muscle MRI spectrum of AD-
HNRNPDL-
related myopathies demonstrating the significant particularities of the disease. We describe two new unrelated Argentinean families, carrying the previously reported c.1132G>C p.(Asp378His)
HNRNPDL
mutation. There was a wide phenotypic spectrum including oligo-symptomatic cases, pure limb girdle muscle involvement or distal lower limb muscle weakness. Scapular winging was the most common finding, observed in all patients. Muscle MRIs of the thigh, at different stages of the disease, showed particular involvement of adductor magnus and vastus besides a constant preservation of the rectus femoris and the adductor longus muscles, defining a novel MRI pattern. Muscle biopsy findings were characterized by the presence of numerous rimmed vacuoles, cytoplasmic bodies, and abundant autophagic material at the histochemistry and ultrastructural levels.
HNRNPDL-
related LGMD D3 results in a wide range of clinical phenotypes from the classic proximal form of LGMD to a more distal phenotype. Thigh MRI suggests a specific pattern. Codon 378 of
HNRNPDL
gene can be considered a mutation hotspot for
HNRNPDL
-related myopathy. Pathologically, the disease can be classified among the autophagic rimmed vacuolar myopathies as with the other multisystem proteinopathies.
Muscle contraction upon nerve stimulation relies on excitation–contraction coupling (ECC) to promote the rapid and generalized release of calcium within myofibers. In skeletal muscle, ECC is ...performed by the direct coupling of a voltage-gated L-type Ca
2+
channel (dihydropyridine receptor; DHPR) located on the T-tubule with a Ca
2+
release channel (ryanodine receptor; RYR1) on the sarcoplasmic reticulum (SR) component of the triad. Here, we characterize a novel class of congenital myopathy at the morphological, molecular, and functional levels. We describe a cohort of 11 patients from 7 families presenting with perinatal hypotonia, severe axial and generalized weakness. Ophthalmoplegia is present in four patients. The analysis of muscle biopsies demonstrated a characteristic intermyofibrillar network due to SR dilatation, internal nuclei, and areas of myofibrillar disorganization in some samples. Exome sequencing revealed ten recessive or dominant mutations in
CACNA1S
(Ca
v
1.1), the pore-forming subunit of DHPR in skeletal muscle. Both recessive and dominant mutations correlated with a consistent phenotype, a decrease in protein level, and with a major impairment of Ca
2+
release induced by depolarization in cultured myotubes. While dominant
CACNA1S
mutations were previously linked to malignant hyperthermia susceptibility or hypokalemic periodic paralysis, our findings strengthen the importance of DHPR for perinatal muscle function in human. These data also highlight CACNA1S and ECC as therapeutic targets for the development of treatments that may be facilitated by the previous knowledge accumulated on DHPR.
Marinesco-Sjögren syndrome is a rare autosomal recessive multisystem disorder featuring cerebellar ataxia, early-onset cataracts, chronic myopathy, variable intellectual disability and delayed motor ...development. More recently, mutations in the SIL1 gene, which encodes an endoplasmic reticulum resident co-chaperone, were identified as the main cause of Marinesco-Sjögren syndrome. Here we describe the results of SIL1 mutation analysis in 62 patients presenting with early-onset ataxia, cataracts and myopathy or combinations of at least two of these. We obtained a mutation detection rate of 60% (15/25) among patients with the characteristic Marinesco-Sjögren syndrome triad (ataxia, cataracts, myopathy) whereas the detection rate in the group of patients with more variable phenotypic presentation was below 3% (1/37). We report 16 unrelated families with a total of 19 different SIL1 mutations. Among these mutations are 15 previously unreported changes, including single- and multi-exon deletions. Based on data from our screening cohort and data compiled from the literature we found that SIL1 mutations are invariably associated with the combination of a cerebellar syndrome and chronic myopathy. Cataracts were observed in all patients beyond the age of 7 years, but might be missing in infants. Six patients with SIL1 mutations had no intellectual disability, extending the known wide range of cognitive capabilities in Marinesco-Sjögren syndrome to include normal intelligence. Modestly constant features were somatic growth retardation, skeletal abnormalities and pyramidal tract signs. Examination of mutant SIL1 expression in cultured patient lymphoblasts suggested that SIL1 mutations result in severely reduced SIL1 protein levels irrespective of the type and position of mutations. Our data broaden the SIL1 mutation spectrum and confirm that SIL1 is the major Marinesco-Sjögren syndrome gene. SIL1 patients usually present with the characteristic triad but cataracts might be missing in young children. As cognitive impairment is not obligatory, patients without intellectual disability but a Marinesco-Sjögren syndrome-compatible phenotype should receive SIL1 mutation analysis. Despite allelic heterogeneity and many families with private mutations, the phenotype related to SIL1 mutations is relatively homogenous. Based on SIL1 expression studies we speculate that this may arise from a uniform effect of different mutations on protein expression.
A 36‐year‐old man with headache and fever Riudavets, Miguel A.; Lía Taratuto, Ana; Pelorosso, Facundo ...
Brain pathology,
July 2018, Letnik:
28, Številka:
4
Journal Article
Abstract
Titin-related myopathies are heterogeneous clinical conditions associated with mutations in TTN. To define their histopathologic boundaries and try to overcome the difficulty in assessing ...the pathogenic role of TTN variants, we performed a thorough morphological skeletal muscle analysis including light and electron microscopy in 23 patients with different clinical phenotypes presenting pathogenic autosomal dominant or autosomal recessive (AR) mutations located in different TTN domains. We identified a consistent pattern characterized by diverse defects in oxidative staining with prominent nuclear internalization in congenital phenotypes (AR-CM) (n = 10), ± necrotic/regenerative fibers, associated with endomysial fibrosis and rimmed vacuoles (RVs) in AR early-onset Emery-Dreifuss-like (AR-ED) (n = 4) and AR adult-onset distal myopathies (n = 4), and cytoplasmic bodies (CBs) as predominant finding in hereditary myopathy with early respiratory failure (HMERF) patients (n = 5). Ultrastructurally, the most significant abnormalities, particularly in AR-CM, were multiple narrow core lesions and/or clear small areas of disorganizations affecting one or a few sarcomeres with M-band and sometimes A-band disruption and loss of thick filaments. CBs were noted in some AR-CM and associated with RVs in HMERF and some AR-ED cases. As a whole, we described recognizable histopathological patterns and structural alterations that could point toward considering the pathogenicity of TTN mutations.
Introduction: Pompe disease is a progressive and debilitating neuromuscular disorder that presents with a heterogeneous array of signs and symptoms including proximal muscle weakness, respiratory ...insufficiency, and/or elevated creatine kinase levels. It mimics other neuromuscular disorders, making its diagnosis challenging and often significantly delayed, thereby increasing morbidity and early mortality of the disease. Methods: Three Pompe disease patients are discussed to highlight the challenging path to diagnosis and the common cluster of symptoms that could lead to timely and accurate diagnosis. Results: After significant delays in diagnosis, Pompe disease was diagnosed on the basis of the pattern of proximal weakness. Conclusions: Suspicion and recognition of the characteristic symptoms of Pompe disease may improve both the timing and accuracy of the diagnosis, which will improve clinical outcomes and minimize disease progression. Muscle Nerve, 2013
We report four heterozygous dynamin 2 (DNM2) mutations in five centronuclear myopathy patients aged 1 to 15 years. They all presented with neonatal hypotonia with weak suckling. Thereafter, their ...phenotype progressively improved. All patients demonstrated muscle weakness prominent in the lower limbs, and most of them also presented with facial weakness, open mouth, arched palate, ptosis, and ophthalmoparesis. Electrophysiology showed only myopathic changes, and muscle biopsies showed central nuclei and type 1 fiber hypotrophy and predominance. Our results expand the phenotypic spectrum of dynamin 2–related centronuclear myopathy from the classic mild form to the more severe neonatal phenotype. Ann Neurol 2007
PDF
