Abstract Thirty-three French-Canadian families with non-dystrophic myotonia were identified. Fifty subjects were recruited and submitted to a complete clinical, electrophysiologic and genetic ...evaluation. Thirteen mutations were identified in CLCN1 and five mutations were identified in SCN4A. Onset in the lower extremities, presence of tongue myotonia and transient weakness suggested recessive CLCN1 mutations. Lid myotonia, absence of hypertrophy and exacerbation with cold temperature suggested SCN4A mutations. Pain was not a feature of dominant CLCN1 mutations while it could be seen in the others, more frequently in SCN4A mutations. Warm up phenomenon, hand grip myotonia, percussion myotonia, lid lag and hormonal effects were not distinguishing features. Repetitive nerve stimulation and short exercise test showed either a large (>50%) or mild-moderate (10–50%) decrement with recessive CLCN1 mutations while they showed only mild or no decrement with dominant CLCN1 and SCN4A mutations. The French-Canadian population shows wide phenotypic and genotypic heterogeneity in non-dystrophic myotonias.
In myotonic dystrophy type 1, several studies have suggested causal relationships between CTG repeat length and the severity of symptoms, such as weakness or myotonia. We aimed to explore these ...relationships in a large population of 144 DM1 patients. All patients underwent clinical and functional assessments using a standardized test for grip strength and myotonia assessment. Myotonia was assessed using a fully automatic software based on mathematical modeling of relaxation force curve. CTG repeat length was statistically correlated with both myotonia and grip strength, which are two major primary neuromuscular symptoms of DM1 patients. However, these relationships are not clinically meaningful and not predictive at the individual level.
The molecular mechanisms underlying the effect of thyroid hormone (T3) on neurite outgrowth are unknown. We recently identified the small GC-box binding protein BTEB (basic transcription ...element-binding protein) as a T3-regulated gene in the developing rat brain. BTEB mRNAs are rapidly (by 1 h) up-regulated by T3 in primary rat embryonic neuronal cultures. Antisense oligodeoxynucleotides (ODNs), added to the cultures, reduced by 60% the level of BTEB mRNA. Addition of BTEB antisense ODNs to the cultures, before the onset of neurite polarity, had no effect on neurite elaboration but significantly decreased, in a dose-dependent manner, the effect of T3 on neurite branching. We then examined the effects of antisense ODNs on a thyroid hormone target neuronal population, i.e. the acetylcholinesterase-positive neurons after the onset of neurite polarity. Exposure to BTEB antisense ODNs completely abolished the effects of T3 on neurite branching and on the elaboration of neuritic filopodia-like structures in acetylcholinesterase cells. By contrast, antisense ODNs did not alter the effect of T3 on neurite length. Our results show that titration of BTEB levels by T3 regulates the degree of neurite branching and that the T3-induced neurite elongation and the T3-induced neurite branching are regulated by distinct mechanisms.
The aim of this study was to evaluate whether magnetic resonance imaging (MRI) can be used as a noninvasive approach to assessment of disease severity and muscle damage in Myotonic Dystrophy type 1 ...(DM1).
The MRI findings in legs of 41 patients with DM1 were evaluated with respect to the tibialis anterior (TA) skeletal muscle impairment. Magnetic resonance imaging findings were compared with TA strength measurements obtained by quantitative manual testing, duration of the disease and with the length of the CTG repeats.
Muscle MRI abnormalities were observed in 80% of DM1 patients, ranging from edema-like abnormalities alone to severe atrophy/fatty replacement. Edema-like abnormalities seem to be an earlier MRI marker of the disease. Fatty infiltration/atrophy correlated with the TA muscle force (r = 0.95), the severity (P = 0.00001) of the disease but not with the duration of the disease (P = 0.3) or the length of the CTG repeats (P > 0.10), measured in peripheral leukocytes. Evaluation of other muscles of the legs revealed that the medial gastrocnemius and soleus muscles were the most frequently and severely affected muscles, while tibialis posterior muscles were relatively spared. Edema-like abnormalities are most frequently observed in the skeletal muscles of the anterior compartment.
Muscle MRI is helpful to depict muscle abnormalities but does not seem to be a reliable indicator of skeletal muscle involvement in DM1 since the decrease in TAmuscle force is not correlated with MRI abnormalities in some patients.
Muscle cell cultures derived from a myotonic dystrophy (DM1) fetus were established in order to determine on the one hand, whether the differentiation of DM1 myoblasts is altered and, on the other ...hand, whether the levels of myotonic dystrophy protein kinase (DMPK) protein is decreased in DM1 muscle cells. DM1 myoblasts isolated from a quadriceps of a 12-weeks old fetus proliferate at a similar rate as normal myoblasts isolated from a quadriceps of an unaffected 15-weeks old fetus but their maturation is altered as shown by the decreased levels in slow myosin heavy chain protein. In contrast, no change was observed in the expression of vimentin, myogenin and embryonic myosin heavy chain. The levels of DMPK transcripts sharply increased during myoblast differentiation and the mutant DMPK transcripts are retained in discrete foci in the nuclei of muscle cells. The levels of 85-kDa DMPK protein was reduced by about 50% in DM1 cells compared with normal cells. Our study demonstrates that delay in DM1 myoblast maturation is associated with nuclear retention of mutant DMPK transcripts and decreased levels of DMPK protein.
Human induced pluripotent stem cells (hiPSCs) are a valuable tool for investigating complex cellular and molecular events that occur in several human diseases. Importantly, the ability to ...differentiate hiPSCs into any human cell type provides a unique way for investigating disease mechanisms such as complex mental health diseases. The in vitro transformation of human lymphocytes into lymphoblasts (LCLs) using the Epstein-Barr virus (EBV) has been the main method for generating immortalized human cell lines for half a century. However, the derivation of iPSCs from LCLs has emerged as an alternative source from which these cell lines can be generated. We show that iPSCs derived from LCLs using the Sendai virus procedure can be successfully differentiated into cardiomyocytes, neurons, and myotubes that express neuron- and myocyte-specific markers. We further show that these cardiac and neuronal cells are functional and generate action potentials that are required for cell excitability. We conclude that the ability to differentiate LCLs into neurons and myocytes will increase the use of LCLs in the future as a potential source of cells for modelling a number of diseases.
•Lymphoblastoids are immortalized cells wildly used in human genetics.•Human pluripotent stem cells are important tools to study several human diseases.•Lymphoblastoids are a new cell source to generate iPSCs.•IPSCs derived lymphoblastoids can be differentiated to neurons and myocytes.
Multiple mutations in the CLCN1 gene coding for the voltage-gated chloride channel have been documented to cause myotonia congenita. We report a kindred featuring an index patient who possesses 2 ...copies of a dominantly inherited mutated CLCN1 allele with a resulting novel phenotypic presentation. The index patient is a boy who presented initially for evaluation at the age of 5 years with a 2-year history of gait problems. Both parents and 3 male siblings were entirely well. Examination revealed a striking diffuse muscular hypertrophy, diffuse mild to moderate weakness, Gower sign, percussion, and grip myotonia. Electromyography confirmed myotonia, and molecular analysis revealed 2 copies of the T310M mutation on the CLCN1 gene. Testing of family members revealed a normal neurological examination without clinical myotonia in all and electromyographic evidence of myotonia and a single copy of the T310M mutation in both parents and 2 siblings. Our kindred is the initial demonstration of the dosage effect of a dominant mutated allele in the CLCN1 gene.
As a first approach to study the molecular mechanisms that underlie the effects of thyroid hormones on the developing brain, we used a cDNA microarray technology to identify early thyroid ...hormone-regulated genes in brain neuronal cultures treated with tri-iodothyronine (T3) for 3 h. We identified three genes that were up-regulated by T3, basic transcription element-binding protein, nuclear pore glycoprotein and bone morphogenetic protein-4 and one that was down-regulated, the neuronal apoptosis-inducing gene. We confirmed that these genes were also regulated by the thyroid state in the developing brain. Our findings enrich our knowledge of signaling pathways regulated by thyroid hormones and open new avenues for studying the molecular mechanisms of thyroid hormones in the developing brain.
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