Myotonic Dystrophy type 1 (DM1) is a multi-system disorder characterized by muscle wasting, myotonia, cardiac conduction defects, cataracts, and neuropsychological dysfunction. DM1 is caused by expansion of a CTG repeat in the 3´untranslated region (UTR) of the Dystrophia Myotonica Protein Kinase (DMPK) gene. A body of work demonstrates that DMPK mRNAs containing abnormally expanded CUG repeats are toxic to several cell types. A core mechanism underlying symptoms of DM1 is that mutant DMPK RNA interferes with the developmentally regulated alternative splicing of defined pre-mRNAs. Expanded CUG repeats fold into ds(CUG) hairpins that sequester nuclear proteins including human Muscleblind-like (MBNL) and hnRNP H alternative splicing factors. DM1 cells activate CELF family member CUG-BP1 protein through hyperphosphorylation and stabilization in the cell nucleus. CUG-BP1 and MBNL1 proteins act antagonistically in exon selection in several pre-mRNA transcripts, thus MBNL1 sequestration and increase in nuclear activity of CUG-BP1 both act synergistically to missplice defined transcripts. Mutant DMPK-mediated effect on subcellular localization, and defective phosphorylation of cytoplasmic CUG-BP1, have additionally been linked to defective translation of p21 and MEF2A in DM1, possibly explaining delayed differentiation of DM1 muscle cells. Mutant DMPK transcripts bind and sequester transcription factors such as Specificity protein 1 leading to reduced transcription of selected genes. Recently, transcripts containing long hairpin structures of CUG repeats have been shown to be a Dicer ribonuclease target and Dicer-induced downregulation of the mutant DMPK transcripts triggers silencing effects on RNAs containing long complementary repeats. In summary, mutant DMPK transcripts alter gene transcription, alternative splicing, and translation of specific gene transcripts, and have the ability to trigger gene-specific silencing effects in DM1 cells. Therapies aimed at reversing these gene expression alterations should prove effective ways to treat DM1.
Dystrophia myotonia type 1 (DM1; Steinert's disease; myotonic dystrophy) is an autosomal dominant disorder due to a large CTG expansion in the 3′-untranslated region (UTR) of the DM protein kinase (DMPK) gene. Transcription of this gene yields a long CUGn-containing mutant (mut) RNA, in which clinical disease is associated with repeats of n=100–5000. Phenomenologically, the expression of mut RNA is correlated with the morphologic observation of ribonucleoprotein precipitates (‘foci') in the nuclei of DMPK-expressing cells. The prevailing view is that the identification of proteins in these foci is the sine qua non of protein–mut RNA interactions. In this viewpoint, I contend that this is an unwarranted inference that falls short in explaining published data. A new model of mut RNA–protein interactions is proposed with distinct binding properties for soluble and insoluble (focus) mut RNA that accommodate these data without exclusions.
mutant RNA; RNA configuration; protein binding; CUGBP; MBNL; transcription factors
Myotonic dystrophy type 1 (MD) is the most common autosomal dominant muscular dystrophy in adults. Cardiac involvement is mainly characterized by conduction abnormalities and arrhythmias. We sought to assess diastolic function in MD patients. Echocardiography-Doppler was performed in Steinert’s patients and in a control group completed by tissue Doppler imaging (TDI). Twenty-six patients with Steinert’s disease were included in the study and were compared to a control group. Mean age was similar in the 2 groups (45.1 years ±10.9 in Steinert’s patients vs 42.1 years ±11 in control group p 0.4). 6 /26 patients with Steinert’s disease disclosed a left ventricular (LV) ejection fraction <50%. Mean left atrial (LA) diameter was statistically different between Steinert’s patients and patients in group control (27.8 mm ±8.5 vs 19.7 mm ±4; P=0.0018). Mean peak E/A mitral ratio was 1.29±0.45 in Steinert’s patients vs 1.36±0.4 in control group (P=0.6). We found an increase of the mitral E deceleration time in Steinert’s patients in comparison with patients in control group (219 ms ±53 vs 176 ms ±29; P=0.013). Mean peak lateral early diastolic velocity Ea was similar in the 2 groups (12.3 cm/s ±3 vs 13.1 cm/s ±3.8; P=0.50). Mean peak septal early diastolic velocity was similar in the 2 groups (11.2 cm/s ±2 vs 10.4±2; P=0.51). We found an increase of the LA diameter and an increase of the mitral deceleration time in Steinert’s patients that suggest diastolic abnormalities.
myotonic dystrophy; echocardiography-Doppler; diastolic function
Myotonic dystrophy is also known as dystrophia myotonica (DM). The condition is composed of at least two clinical disorders with overlapping phenotypes and distinct molecular genetic defects: myotonic dystrophy type 1, the classic disease originally described by Steinert, and myotonic dystrophy type 2, also called proximal myotonic myopathy (PROMM). Mega cisterna magna is thought to be an anatomic variant with no clinical significance. We report a rare case of type 1 dystrophia myotonica in combination with mega cisterna magna.
Dystrophia myotonica; mega cisterna magna; congenital myotonic dystrophy
Myotonic dystrophy type 1 (DM1) is caused by CUG triplet expansions in the 3′ UTR of dystrophia myotonica protein kinase (DMPK) messenger ribonucleic acid (mRNA). The etiology of this multi-systemic disease involves pre-mRNA splicing defects elicited by the ability of the CUG-expanded mRNA to ‘sponge’ splicing factors of the muscleblind family. Although nuclear aggregation of CUG-containing mRNPs in distinct foci is a hallmark of DM1, the mechanisms of their homeostasis have not been completely elucidated. Here we show that a DEAD-box helicase, DDX6, interacts with CUG triplet-repeat mRNA in primary fibroblasts from DM1 patients and with CUG–RNA in vitro. DDX6 overexpression relieves DM1 mis-splicing, and causes a significant reduction in nuclear DMPK-mRNA foci. Conversely, knockdown of endogenous DDX6 leads to a significant increase in DMPK-mRNA foci count and to increased sequestration of MBNL1 in the nucleus. While the level of CUG-expanded mRNA is unaffected by increased DDX6 expression, the mRNA re-localizes to the cytoplasm and its interaction partner MBNL1 becomes dispersed and also partially re-localized to the cytoplasm. Finally, we show that DDX6 unwinds CUG-repeat duplexes in vitro in an adenosinetriphosphate-dependent manner, suggesting that DDX6 can remodel and release nuclear DMPK messenger ribonucleoprotein foci, leading to normalization of pathogenic alternative splicing events.
Myotonic dystrophy (DM) is the most common adult muscular dystrophy, characterized by autosomal dominant progressive myopathy, myotonia and multiorgan involvement. To date two distinct forms caused by similar mutations have been identified. Myotonic dystrophy type 1 (DM1, Steinert's disease) was described more than 100 years ago and is caused by a (CTG)n expansion in DMPK, while myotonic dystrophy type 2 (DM2) was identified only 18 years ago and is caused by a (CCTG)n expansion in ZNF9/CNBP. When transcribed into CUG/CCUG-containing RNA, mutant transcripts aggregate as nuclear foci that sequester RNA-binding proteins, resulting in spliceopathy of downstream effector genes. Despite clinical and genetic similarities, DM1 and DM2 are distinct disorders requiring different diagnostic and management strategies. DM1 may present in four different forms: congenital, early childhood, adult onset and late-onset oligosymptomatic DM1. Congenital DM1 is the most severe form of DM characterized by extreme muscle weakness and mental retardation. In DM2 the clinical phenotype is extremely variable and there are no distinct clinical subgroups. Congenital and childhood-onset forms are not present in DM2 and, in contrast to DM1, myotonia may be absent even on EMG. Due to the lack of awareness of the disease among clinicians, DM2 remains largely underdiagnosed. The delay in receiving the correct diagnosis after onset of first symptoms is very long in DM: on average more than 5 years for DM1 and more than 14 years for DM2 patients. The long delay in the diagnosis of DM causes unnecessary problems for the patients to manage their lives and anguish with uncertainty of prognosis and treatment.
Myotonic dystrophy type 1 (Dm1); myotonic dystrophy type 2 (Dm2); management
Myotonic dystrophy is an autosomal dominant, multisystem disorder that is characterized by myotonic myopathy. The symptoms and severity of myotonic dystrophy type l (DM1) ranges from severe and congenital forms, which frequently result in death because of respiratory deficiency, through to late-onset baldness and cataract. In adult patients, cardiac conduction abnormalities may occur and cause a shorter life span. In subsequent generations, the symptoms in DM1 may present at an earlier age and have a more severe course (anticipation). In myotonic dystrophy type 2 (DM2), no anticipation is described, but cardiac conduction abnormalities as in DM1 are observed and patients with DM2 additionally have muscle pain and stiffness. Both DM1 and DM2 are caused by unstable DNA repeats in untranslated regions of different genes: A (CTG)n repeat in the 3'-UTR of the DMPK gene and a (CCTG)n repeat in intron 1 of the CNBP (formerly ZNF9) gene, respectively. The length of the (CTG)n repeat expansion in DM1 correlates with disease severity and age of onset. Nevertheless, these repeat sizes have limited predictive values on individual bases. Because of the disease characteristics in DM1 and DM2, appropriate molecular testing and reporting is very important for the optimal counseling in myotonic dystrophy. Here, we describe best practice guidelines for clinical molecular genetic analysis and reporting in DM1 and DM2, including presymptomatic and prenatal testing.
Myotonic dystrophy type 1 (Steinert's disease) is a multisystem disorder with autosomal dominant inheritance. This disease is associated with the presence of an abnormal expansion of a cytosine thymine-guanine (CTG) trinucleotide repeat on chromosome 19q13.3. Because of rhythmic complications, the place for systematic electrophysiological study (EPS) has to be discussed.
It is well known that myotonic dystrophy type 1 (DM1) - Curschmann-Steinert disease - is associated with white matter lesions in the brain. Further, DM1 patients may suffer from cardiac involvement and cardioembolic strokes. We report on the unique case of an adult-onset DM1 without cardiac or vascular abnormalities presenting with stroke-like episodes.
A 40 y old white female was admitted twice to our stroke unit with apoplectic dizziness, nausea, headaches, and numbness in the right arm. She was suffering from type 2 diabetes, cataract, and endometriosis. Magnetic resonance imaging (MRI) revealed confluent white matter lesions in all cerebral lobes. There was no hyperintensity on diffusion-weighted imaging (DWI) and no gadolinium enhancement. Cerebrospinal fluid was normal. Surprisingly, myotonic discharges were detected in electromyography (EMG). Genetic testing revealed 200 ± 10 CTG repeats in the dystrophia myotonica protein kinase (DMPK) gene on chromosome 19 and DM1 was diagnosed.
DM1 may be the cause of cerebral white matter lesions. This is the first case of DM1 presenting with stroke-like episodes.
Myotonic dystrophy of Steinert, DM1, is the most common adult muscular dystrophy and generally is not associated to development on multiple site neoplasm. Von Hippel-Lindau (VHL) disease is a dominantly inherited familial cancer syndrome that is associated to tumors such as hemangioblastoma of the retina or central nervous system, clear-cell renal carcinoma (RCC) and endocrine tumors, most commonly pheochromocytoma and non-secretory pancreatic islet cell cancers. No data exist in literature describing the coexistence of both DM1 and VHL.
PRESENTATION OF CASE
Herein we report a case of renal and pancreatic neoplasm in a young adult female affected by DM1 and VHL simultaneously.
DM1 is due to an unstable trinucleotide (CTG) expansion in the 30 antranslated region of the dystrophia myotonica-protein kinase (DMPK) gene, located on chromosome 19q13.3. Several molecular mechanisms thought to be determining the classical DM phenotype have been shown. VHL disease is characterized by marked phenotypic variability and the most common tumors are hemangioblastomas of the retina or central nervous system, clear-cell renal carcinoma (RCC) and endocrine tumors, most commonly pheochromocytoma and non-secretory pancreatic islet cell cancers. The pancreatic manifestations seen in patients with VHL disease are divided into 2 categories: pancreatic neuroendocrine tumor (PNET) as solid tumors, and cystic lesions, including a simple cyst and serous cystadenoma. The surgical approach for these cistic lesions is to consider as golden standard. Blansfield has proposed 3 criteria to predict metastatic disease of PNET in patients with VHL disease: (1) tumor size greater than or equal to 3 cm; (2) presence of a mutation in exon 3; and (3) tumor doubling time less than 500 d. If the patient has none of these criteria the patient could be followed with physical examination and radiological surveillance on a 2/3 years base.4 If the patient has 1 criterion, the patient should be followed more closely every 6 months to 1 year. If the patient has 2 or 3 criteria, the patient should be considered for surgery given the high risk of future malignancy. Our patient owned only one criterion but in presence of a second malignant tumor. Our hypothesis for this rare findings is that both DM and VHL might be derived from genetic aberration and these might be linked to a major cancer susceptibility. As far as we know this is the first confirmed case of RCC and neuroendocrine pancreatic cancer occurring concurrently with VHL and, at the same time, DM1. According to this case report and the literature data a VHL should be ruled out in the presence of RCC presenting along with pancreatic cysts/tumor.
As far as we know this is the first confirmed case of RCC and neuroendocrine pancreatic cancer occurring concurrently with VHL and, at the same time, DM1. Our hypothesis for the unusual findings is that both DM and VHL derived from genetic aberration and these are linked to a major cancer susceptibility.
Von Hippel–Lindau; Myotonic dystrophy of Steinert; Pancreatic neuroendocrine tumor; Renal clear cell carcinomal neoplasm
Serum insulin, blood sugar, and growth hormone levels were measured in response to a 50g oral glucose tolerance test in 10 patients with proven dystrophia myotonica. Three patients belonged to one family; seven patients had no known family history of the disease. One patient, a chronic invalid aged 56 years, produced a mild diabetic glucose tolerance curve and a delayed prolonged rise in serum insulin. Six of the group, including the three affected members from one family, exhibited normal glucose tolerance and fasting serum insulin values, but a markedly exaggerated rise in peripheral insulin levels maximal at 30 and 60 min. This abnormality showed no correlation with age of onset of the disease nor with severity of the muscle weakness. Growth hormone levels were normal in all of the patients studied. It is concluded that an excessive rise in circulating immunoreactive insulin in response to glucose is a common abnormality in dystrophia myotonica and reflects genetic heterogeneity in this condition. Futhermore, if the index patient in a family demostrates this abnormality, it is suggested that the 30- or 60-min blood insulin level during a glucose tolerance test is a useful methold of intra-family screen-ing for asymptomatic heterozygotes at an early stage before the development of physical defects.
Seven patients with dystrophia myotonica were investigated using neurophysiological combined with histochemical techniques to elucidate motor unit properties in foot extensor muscles, which are often involved in the early stages of this disorder. For the 25 extensor digitorum brevis motor units studied the axonal conduction velocity, the axonal refractory period and the voluntary firing properties were within normal limits. However, high threshold motor units were not observed and the mean value of the axonal conduction velocities was lower (p less than 0.02) for the dystrophia myotonica motor units when compared with corresponding data from healthy subjects. There were also signs of impaired impulse propagation in the terminal part of the motor unit. In muscle biopsy specimens from the anterior tibial muscle, fibre type composition and structure were demonstrated using enzyme histochemical techniques for adenosine-triphosphate and immunohistochemical techniques for identification of the types of myosin isoform present. The histochemical findings indicated a type I fibre dominance, which was most obvious in the more seriously affected muscles. Neonatal myosin was observed preferentially in small but also in some normal sized fibres. Furthermore, some ring fibres were present and these showed staining with antineonatal myosin in their superficial portion. This indicates that an abnormal regeneration is one cause of the myopathic appearance of the muscle fibres in dystrophia myotonica. These investigations show that there is a reduced proportion of type II motor units in foot extensor muscles involved in the myopathy in dystrophia myotonica although it cannot definitely be established whether this is due to a loss of high threshold type II motor units or type II to type I transformation.
Levels of immunoglobulins IgG, IgA, and IgM were measured in 38 patients with myotonic dystrophy, in normal members of their families, and in matched controls. Log IgG was significantly reduced in the patients. IgG investigation provides a further parameter to appraise the status of apparently unaffected members of myotonic dystrophy families.
Myotonic dystrophy type 1 (DM1) is an autosomal dominant genetic multisystem disorder and the commonest adult-onset form of muscular dystrophy. DM1 results from the expansion of an unstable trinucleotide cytosine-thymine-guanine (CTG) repeat mutation. CTG repeats in DM1 patients can range from 50 to several thousands, with a tendency toward increased repeats with successive generations (anticipation). Associated findings can include involvements in almost every systems, including the brain, and cognitive abnormalities occur in the large majority of patients. The objectives are to describe and compare the intellectual abilities of a large sample of DM1 patients with mild and classic adult-onset phenotypes, to estimate the validity of the Wechsler Adult Intelligence Scale-Revised (WAIS-R) in DM1 patients with muscular weakness, and to appraise the relationship of intelligence quotient (IQ) to CTG repeat length, age at onset of symptoms, and disease duration.
A seven-subtest WAIS-R was administered to 37 mild and 151 classic adult-onset DM1 patients to measure their Full-Scale (FSIQ), Verbal (VIQ) and Performance IQ (PIQ). To control for potential bias due to muscular weakness, Standard Progressive Matrices (SPM), a motor-independent test of intelligence, were also completed.
Total mean FSIQ was 82.6 corresponding to low average IQ, and 82% were below an average intelligence. Mild DM1 patients had a higher mean FSIQ (U=88.7 vs 81.1, p<0.001), VIQ (U=87.8 vs 82.3, p=0.001), and PIQ (U=94.8 vs 83.6, p<0.001) than classic adult-onset DM1 patients. In both mild and classic adult-onset patients, all subtests mean scaled scores were below the normative sample mean. FSIQ also strongly correlate with SPM (rs=0.67, p<0.001), indicating that low intelligence scores are not a consequence of motor impairment. FSIQ scores decreased with both the increase of (CTG)n (rs=−0.41, p<0.001) and disease duration (rs=−0.26, p=0.003).
Results show that intellectual impairment is an extremely common and important feature in DM1, not only among the classic adult-onset patients but also among the least severe forms of DM1, with low IQ scores compared to general reference population. Health care providers involved in the follow-up of these patients should be aware of their intellectual capacities and should adapt their interventions accordingly.
Myotonic dystrophy; Phenotype; Central nervous system; Neuropsychology; Intellectual disability; Dystrophie myotonique; Phénotype; Système nerveux central; Neuropsychologie; Déficience intellectuelle
Hypertrophic cardiomyopathy is a heterogeneous disease with autosomal dominant Mendelian inheritance. In 1989, the 1st locus for hypertrophic cardiomyopathy was mapped to cardiac myosin genes located on chromosome 14q1. Soon, several mutations that cosegregated with inheritance of the disease were identified in the beta-myosin heavy chain gene, or MHY7. More than 30 missense mutations and 1 deletion mutation in the beta-myosin heavy chain gene have since been described. Recently, expression of both the mutant beta-myosin heavy chain mRNA and the mutant protein has been shown in the cardiac and skeletal muscles of individuals with hypertrophic cardiomyopathy. Characterization of the clinical features of beta-myosin heavy chain mutations has shown that certain mutations, such as Arg403Gln and Arg719Trp mutations, are associated with high rate of sudden cardiac death. In addition to the beta-myosin heavy chain gene, 3 new loci for hypertrophic cardiomyopathy have recently been described, but the candidate genes have not yet been identified. Dilated cardiomyopathy can be inherited as an autosomal dominant, autosomal recessive, and X-linked disease. The familial form of dilated cardiomyopathy comprises approximately 20% of the cases of idiopathic cardiomyopathy. Echocardiographic abnormalities such as left ventricular enlargement are present in 10% of asymptomatic relatives. No gene for familial dilated cardiomyopathy has been identified, but linkage studies using polymorphic, short-tandem repeat markers are ongoing. Dilated cardiomyopathy is a common manifestation of Duchenne/Becker muscular dystrophy. Heart failure is a common cause of death in the affected individuals. The gene responsible for this disease is the dystrophin gene located on X chromosome. There have been reports in these patients of several dystrophin-gene deletion mutations, which result in a decrease in the expression of the dystrophin protein in the cardiac and skeletal tissues. X-linked cardiomyopathy, in which the disease is restricted to the heart, has also been linked to the dystrophin gene. Myotonic dystrophy is an autosomal dominant disease that commonly involves the myocardium and the conduction tissue, resulting in conduction defects and heart failure. Sudden cardiac death is the most common cause of mortality in patients with myotonic dystrophy. Recently, the myotonin protein kinase gene located on chromosome 19 was identified as the gene responsible for this disease. Expansion of the number of trinucleotide repeats in the myotonin protein kinase gene results in myotonic dystrophy. Mutations in mitochondrial DNA have been associated with hypertrophic and dilated cardiomyopathy. The inheritance of mitochondrial cardiomyopathy is maternal and the disease is associated with certain systemic disorders.
Type 1 myotonic dystrophy (DM1) is an autosomal-dominant inherited disorder with a multisystem involvement, caused by an abnormal expansion of the CTG sequence of the dystrophic myotonia protein kinase (DMPK) gene. DM1 is a variable multisystem disorder with muscular and nonmuscular abnormalities. Increasingly, endocrine abnormalities, such as gonadal, pancreatic, and adrenal dysfunction are being reported. But, Electrolytes imbalance is a very rare condition in patients with DM1 yet. Herein we present a 42-yr-old Korean male of DM1 with abnormally elevated serum sodium and potassium. The patient had minimum volume of maximally concentrated urine without water loss. It was only cured by normal saline hydration. The cause of hypernatremia was considered by primary hypodipsia. Hyperkalemic conditions such as renal failure, pseudohyperkalemia, cortisol deficiency and hyperkalemic periodic paralysis were excluded. Further endocrine evaluation suggested selective hyperreninemic hypoaldosteronism as a cause of hyperkalemia.
Myotonic Dystrophy; Hypernatremia; Hyperkalemia
BACKGROUND--Breathlessness appears to be closely related to the perception of the outgoing motor command to breathe and should be increased in the presence of muscle weakness. However, breathlessness is not a common symptom in patients with chronic muscle disease who have weak respiratory muscles. The factors that determine the perception of respiratory effort in such patients have not been examined. METHODS--The inspiratory effort sensation during resting breathing and progressive hypercapnia was investigated in 12 patients with dystrophia myotonica with weak respiratory muscles (nine men and three women of mean (SD) age 41.1 (10.5) years; maximum inspiratory pressure 43.1 (17.2) cm H2O) and an age and sex matched control group of normal subjects of mean age 39.6 (10.6) years and a maximum inspiratory pressure of 123 (15.2) cm H2O. RESULTS--During resting breathing with a mouthpiece no differences were seen in inspiratory effort sensation, mouth occlusion pressure, or tidal volume, but inspiratory time and cycle duration were significantly shorter in the patients with dystrophia. Minute ventilation (VE) was significantly higher in the patients (15.8 (4.0) l/min v 12.5 (2.6) l/min), while resting breathing was no more variable in the patients than in controls. The ventilatory response to carbon dioxide (VE/PCO2) was not significantly lower in the patients (14.9 (6.9) l/min/kPa) than in the controls (17.4 (4.3) l/min/kPa). Effort sensation responses to carbon dioxide driven breathing were similar in the control subjects and the patients. With regression analysis of pooled data neither maximum inspiratory pressure nor disease state contributed to perceived inspiratory effort during hypercapnia. CONCLUSIONS--Moderately severe global respiratory muscle weakness does not appear to influence the ventilatory response to rising carbon dioxide tension or the perception of inspiratory effort in patients with dystrophia myotonica.
A study has been performed on 124 first degree relatives of 38 index patients with dystrophia myotonica in order to assess means of detecting heterozygotes before neurological complaints. Some or all of the following tests have been performed on the relatives: clinical examination, electromyography, slit-lamp examination, radiography of the skull, electrocardiography, serum insulin, and serum immunoglobulin levels. There is evidence that abnormalities in symptomless heterozygotes may be detected by slit-lamp examination, electromyography, and immunoglobulin concentration, and this is probably the order of usefulness of the test in early recognition of the disease. In this study 13 previously undetected heterozygotes have been identified: six as a result of neurological examination, four by both electromyography and slit-lamp examination, and three by slit-lamp examination alone. Abnormalities detected by these tests appear to be independently manifest, so that they will probably be more useful in combination than singly. The family data give a maximum estimate for incidence of mutations among index cases of one quarter, lower than previously suggested. The estimation of immunoglobulins in 45 patients showed significant deficiency, as compared with controls, not only of IgG but also of IgM, and there was an insignificant trend for IgA to be low too. This suggests that the abnormally rapid catabolism of immunoglobulin, previously reported, is not specific for IgG.
Somatosensory evoked potentials (SEPs) were recorded in a group of 21 patients with dystrophia myotonica and in a group of controls. Those with dystrophia myotonica had longer absolute peak latencies due to slower peripheral conduction. SEP abnormalities revealed peripheral and/or central conduction delays in 33% of the dystrophia myotonica subjects. There was no apparent relationship between the clinical severity of the disease and SEP abnormality.
Five preterm babies with the neonatal form of dystrophia myotonica are reported. In addition to the generally accepted signs and symptoms of the disease, two other features were present in these patients; oedema was notable in all 5 babies and 4 had unexplained haematomas. It is suggested that premature birth may be a result of severe involvement and that prematurity further aggravates the symptoms.
Tumorigenesis is a multi-step process due to an accumulation of genetic mutations in multiple genes in diverse pathways which ultimately lead to loss of control over cell growth. It is well known that inheritance of rare germline mutations in genes involved in tumorigenesis pathways confer high lifetime risk of neoplasia in affected individuals. Furthermore, a substantial number of multiple malformation syndromes include cancer susceptibility in their phenotype. Studies of the mechanisms underlying these inherited syndromes have added to the understanding of both normal development and the pathophysiology of carcinogenesis. Myotonic dystrophy (DM) represents a group of autosomal dominant, multisystemic diseases that share the clinical features of myotonia, muscle weakness, and early-onset cataracts. Myotonic dystrophy type 1 (DM1) and myotonic dystrophy type 2 (DM2) result from unstable nucleotide repeat expansions in their respective genes. There have been multiple reports of tumors in individuals with DM, most commonly benign calcifying cutaneous tumors known as pilomatricomas. We provide a summary of the tumors reported in DM and a hypothesis for a possible mechanism of tumorigenesis. We hope to stimulate further study into the potential role of DM genes in tumorigenesis, and help define DM pathogenesis, and facilitate developing novel treatment modalities.
Tumorigenesis; Myotonic dystrophy; Repeat expansion disorders; Pilomatricoma; β-Catenin
Myotonic dystrophy (DM) is the most common form of muscular dystrophy and is caused by expansion of a CTG trinucleotide repeat on human chromosome 19. Patients with DM develop atrioventricular conduction disturbances, the principal cardiac manifestation of this disease. The etiology of the pathophysiological changes observed in DM has yet to be resolved. Haploinsufficiency of myotonic dystrophy protein kinase (DMPK), DM locus-associated homeodomain protein (DMAHP) and/or titration of RNA-binding proteins by expanded CUG sequences have been hypothesized to underlie the multi-system defects observed in DM. Using an in vivo murine electrophysiology study, we show that cardiac conduction is exquisitely sensitive to DMPK gene dosage. DMPK–/– mice develop cardiac conduction defects which include first-, second-, and third-degree atrioventricular (A–V) block. Our results demonstrate that the A–V node and the His-Purkinje regions of the conduction system are specifically compromised by DMPK loss. Importantly, DMPK+/– mice develop first-degree heart block, a conduction defect strikingly similar to that observed in DM patients. These results demonstrate that DMPK dosage is a critical element modulating cardiac conduction integrity and conclusively link haploinsufficiency of DMPK with cardiac disease in myotonic dystrophy.
Myotonic dystrophy type 1 (DM1) is the most common muscular dystrophy in adults. It is caused by an expanded (CTG)n tract in the 3′ UTR of the Dystrophia Myotonica Protein Kinase (DMPK) gene. This causes nuclear retention of the mutant mRNA into ribonuclear foci and sequestration of interacting RNA-binding proteins (such as muscleblind-like 1 (MBNL1)). More severe congenital and childhood-onset forms of the disease exist but are less understood than the adult disease, due in part to the lack of adequate animal models. To address this, we utilized transgenic mice over-expressing the DMPK 3′ UTR as part of an inducible RNA transcript to model early-onset myotonic dystrophy. In mice in which transgene expression was induced during embryogenesis, we found that by two weeks after birth, mice reproduced cardinal features of myotonic dystrophy, including myotonia, cardiac conduction abnormalities, muscle weakness, histopathology and mRNA splicing defects. Notably, these defects were more severe than in adult mice induced for an equivalent period of exposure to RNA toxicity. Additionally, the utility of the model was tested by over-expressing MBNL1, a key therapeutic strategy being actively pursued for treating the disease phenotypes associated with DM1. Significantly, increased MBNL1 in skeletal muscle partially corrected myotonia and splicing defects present in these mice, demonstrating the responsiveness of the model to relevant therapeutic interventions. Furthermore, these results also represent the first murine model for early-onset DM1 and provide a tool to investigate the effects of RNA toxicity at various stages of development.
Myotonic dystrophy type 1 (DM1) is caused by an unstable CTG repeat expansion in the 3′UTR of the DM protein kinase (DMPK) gene. DMPK transcripts carrying CUG expansions form nuclear foci and affect splicing regulation of various RNA transcripts. Furthermore, bidirectional transcription over the DMPK gene and non-conventional RNA translation of repeated transcripts have been described in DM1. It is clear now that this disease may involve multiple pathogenic pathways including changes in gene expression, RNA stability and splicing regulation, protein translation, and micro–RNA metabolism. We previously generated transgenic mice with 45-kb of the DM1 locus and >300 CTG repeats (DM300 mice). After successive breeding and a high level of CTG repeat instability, we obtained transgenic mice carrying >1,000 CTG (DMSXL mice). Here we described for the first time the expression pattern of the DMPK sense transcripts in DMSXL and human tissues. Interestingly, we also demonstrate that DMPK antisense transcripts are expressed in various DMSXL and human tissues, and that both sense and antisense transcripts accumulate in independent nuclear foci that do not co-localize together. Molecular features of DM1-associated RNA toxicity in DMSXL mice (such as foci accumulation and mild missplicing), were associated with high mortality, growth retardation, and muscle defects (abnormal histopathology, reduced muscle strength, and lower motor performances). We have found that lower levels of IGFBP-3 may contribute to DMSXL growth retardation, while increased proteasome activity may affect muscle function. These data demonstrate that the human DM1 locus carrying very large expansions induced a variety of molecular and physiological defects in transgenic mice, reflecting DM1 to a certain extent. As a result, DMSXL mice provide an animal tool to decipher various aspects of the disease mechanisms. In addition, these mice can be used to test the preclinical impact of systemic therapeutic strategies on molecular and physiological phenotypes.
Myotonic dystrophy type 1 (DM1) is caused by the abnormal expansion of a CTG repeat located in the DM protein kinase (DMPK) gene. DMPK transcripts carrying CUG expansions form toxic nuclear foci that affect other RNAs. DM1 involve multiple pathogenic pathways including changes in gene expression, RNA stability and splicing regulation, protein translation, and micro–RNA metabolism. We previously generated transgenic mice carrying the human DM1 locus and very large expansions >1,000 CTG (DMSXL mice). Here we described for the first time, the expression pattern of the DMPK sense transcripts in DMSXL and human tissues. We also demonstrate that DMPK antisense transcripts are expressed in various tissues from DMSXL mice and human. Both sense and antisense transcripts form nuclear foci. DMSXL mice showed molecular DM1 features such as foci and mild splicing defects as well as muscles defects, reduced muscle strength, and lower motor performances. These mice recapitulate some molecular features of DM1 leading to physiological abnormalities. DMSXL are not only a tool to decipher various mechanisms involved in DM1 but also to test the preclinical impact of systemic therapeutic strategies.
Myotonic dystrophy type 1 (DM1) is associated with one of the most highly unstable CTG•CAG repeat expansions. The formation of further repeat expansions in transgenic mice carrying expanded CTG•CAG tracts requires the mismatch repair (MMR) proteins MSH2 and MSH3, forming the MutSβ complex. It has been proposed that binding of MutSβ to CAG hairpins blocks its ATPase activity compromising hairpin repair, thereby causing expansions. This would suggest that binding, but not ATP hydrolysis, by MutSβ is critical for trinucleotide expansions. However, it is unknown if the MSH2 ATPase activity is dispensible for instability. To get insight into the mechanism by which MSH2 generates trinucleotide expansions, we crossed DM1 transgenic mice carrying a highly unstable >(CTG)300 repeat tract with mice carrying the G674A mutation in the MSH2 ATPase domain. This mutation impairs MSH2 ATPase activity and ablates base–base MMR, but does not affect the ability of MSH2 (associated with MSH6) to bind DNA mismatches. We found that the ATPase domain mutation of MSH2 strongly affects the formation of CTG expansions and leads instead to transmitted contractions, similar to a Msh2-null or Msh3-null deficiency. While a decrease in MSH2 protein level was observed in tissues from Msh2G674 mice, the dramatic reduction of expansions suggests that the expansion-biased trinucleotide repeat instability requires a functional MSH2 ATPase domain and probably a functional MMR system.
Myotonic dystrophy type 1 is a neuromuscular disease characterized by highly variable clinical manifestations, including muscular and neuropsychological symptoms. DM1 results from the dramatic expansion of an unstable CTG repeat in the DMPK gene. Longer CTG repeats cause a more severe form of the disease and an earlier age of onset. The DNA mismatch repair proteins MSH2 and MSH3 are known to be major players in the formation of trinucleotide expansions. Nevertheless, the mode of action of these proteins remains elusive. In order to get further insight into the role of MSH2 in the formation of CTG expansions, we used a mouse model carrying a mutation in the conserved ATPase domain of Msh2. This mutation affects the function of this domain and alters the DNA repair mismatch activity. After breeding of these mice with mice carrying highly unstable CTG repeats, we found that the ATPase domain mutation of MSH2 strongly affects the formation of CTG expansions. Our findings show that expansion-biased trinucleotide repeat instability requires a functional MSH2 ATPase domain and support the hypothesis, according to which a functional MMR activity is required to generate expansions.