Myotonia in DNM2-Related Centronuclear Myopathy
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J Neural Transm (2014) 121:549–553 DOI 10.1007/s00702-013-1140-8 NEUROLOGY AND PRECLINICAL NEUROLOGICAL STUDIES - ORIGINAL ARTICLE Myotonia in DNM2-related centronuclear myopathy Ron Dabby • Menachem Sadeh • Ronit Gilad • Karin Jurkat-Rott • Frank Lehmann-Horn • Esther Leshinsky-Silver Received: 26 October 2013 / Accepted: 12 December 2013 / Published online: 24 December 2013 Ó Springer-Verlag Wien 2013 Abstract Centronuclear myopathy (CNM) is a rare Keywords Dynamin 2 (DNM2) Á Myotonia Á hereditary myopathy characterized by centrally located Centronuclear myopathy Á Charcot–Marie–Tooth (CMT) muscle fiber nuclei. Mutations in the dynamin 2 (DNM2) neuropathy Á Electromyography gene are estimated to account for about 50 % of CNM cases. Electromyographic recordings in CNM may show myopathic motor unit potentials without spontaneous Introduction activity at rest. Myotonic discharges, a distinctive electrical activity caused by membrane hyperexcitability, are char- Myotonia, a condition characterized by impaired relaxation acteristic of certain neuromuscular disorders. Such activity of contracted skeletal muscles, can occur in certain neu- has been reported in only one CNM case without a known romuscular disorders. It is a disorder of muscle membrane genetic cause. We sequenced the DNM2 gene and the hyperexcitability that is caused by sarcolemmal ion chan- genes associated with myotonia (CLCN1, SCN4A, DMPK nel dysfunction (Lehmann-Horn et al. 1995; Jurkat-Rott and ZNF9) in a sporadic adult patient with CNM and and Lehmann-Horn 2005; Lossin and George 2008). myotonic discharges. Sequencing the entire coding region Hyperexcitable sarcolemma can result from specific and exon–intron boundaries revealed a heterozygous mutations in the ion channel genes, particularly the sodium c.1106g-a substitution in exon 8, resulting in a R369Q and chloride channels, or as a part of other specific muscle change in the DNM2. Sequencing the CLCN1, SCN4A, disorders, such as the myotonic dystrophies. Myotonic DMPK and ZNF9 genes ruled out mutations in these genes. discharges, without clinical myotonia, have been reported This is the first report of DNM2-related CNM presenting in patients with myofibrillary myopathy (Hanisch et al. with myotonia. The diagnosis of CNM should be consid- 2013). However, the presence of myotonia in association ered in patients with myotonic discharges of an unknown with myopathy, may serve as a valuable tool in the dif- cause. ferential diagnosis of neuromuscular diseases. The centronuclear myopathies (CNM) are inherited heterogeneous neuromuscular disorders, characterized by numerous centrally located nuclei in muscle fibers. R. Dabby (&) Á M. Sadeh Á R. Gilad X-linked myotubular myopathy is a severe disease with Departments of Neurology, Edith Wolfson Medical Center, infantile onset, characterized by marked weakness and 58100 Holon, Israel respiratory failure, and caused by mutations in the myo- e-mail: [email protected] tubularin gene (Laporte et al. 1996). Autosomal dominant K. Jurkat-Rott Á F. Lehmann-Horn and recessive forms exist with mutations in the dynamin 2 Department of Neurophysiology, Ulm University, (DNM2) (Bitoun et al. 2005), amphiphysin 2 (BIN1) (Nicot Ulm, Germany et al. 2007), and the ryanodine receptor genes (RYR1) (Jungbluth et al. 2007). E. Leshinsky-Silver Molecular Genetic Laboratory, Affiliated with Sackler Faculty of In only a few case reports myotonic discharges were Medicine, Tel Aviv University, Tel Aviv, Israel associated with centronuclear myopathy. Some of the 123 550 R. Dabby et al. reported patients had cataract at young age. In none of and had to use her arms to get up from a squatting position. them myotonic dystrophy was excluded by genetic studies, Deep tendon reflexes were normal, with flexor plantar and no genetic studies for DNM2 mutation were available response. Neither spontaneous or percussion myotonia nor then (Hawkes and Absolon 1975, Gil-Peralta et al. 1978, muscle hypertrophy were observed. Sensation was normal Vallat et al. 1985, Zanoteli et al. 1998). Here, we describe to all modalities. Physical examination was normal, there the first patient with DNM2-related CNM with myotonic was no skin rash. discharges. Serum creatine kinase (CK) was initially 11,000 IU/L (normal values \ 200), however, further values on follow- up were 800–1,200 IU/L. Motor and sensory nerve con- Case report duction studies were normal. Electromyogram (EMG) showed numerous myotonic discharges, without fibrilla- A 27-year-old woman, born in Ukraine to non-consan- tions or positive sharp waves, mainly in the proximal guineous parents of Jewish origin, immigrated to Israel at muscles of the upper and lower extremities. The myotonic age 24. Her past medical history is unremarkable, except discharges were evoked by inserting or moving the needle for orthopedic surgery in her left knee in 2003. Her father, electrode, they waxed and waned with variation of ampli- who died of a stroke at age 55, had difficulties walking and tude and frequency (Fig. 1). Motor unit potentials (MUPs) rising from a chair, which had never been investigated. were of short duration and low amplitude, particularly in Otherwise, no other family members had neurological the quadriceps muscles, with early and nearly full recruit- illnesses. ment. These findings were consistent with the diagnosis of The patient was referred to the Department of Neurol- myopathy with myotonia. Therefore, genetic testing for ogy at Wolfson Medical Center in August 2011 for eval- myotonic dystrophy types I (DM1) and II (DM2) were uation of muscle weakness in the lower extremities that had performed. The results showed normal repeat lengths in the been progressing over one year. In mid 2010, she experi- DMPK and ZNF9 genes, ruling out these diseases. A repeat enced severe pain in her left thigh shortly after strenuous EMG study several months later showed similar abundant exercise in a fitness center. After the pain subsided she myotonic discharges in the upper and lower limb muscles. noticed difficulties climbing stairs and rising from a sitting position, which slowly progressed with time. She denied muscle twitches or cramps. She noticed neither weakness Materials and methods in her upper extremities nor difficulties walking on flat surfaces. There were no sensory, visual or bulbar Muscle biopsy symptoms. Neurologic examination revealed intact cranial nerves Part of the muscle was fixed with formalin and embedded without ptosis or ophthalmoparesis, and normal strength of in paraffin. Another sample was frozen in isopentane the neck muscles. In the upper extremities, proximal and chilled in liquid nitrogen. Seven micrometer thick trans- distal muscle weakness was symmetric, 4/5 (Medical verse sections were stained with haematoxylin and eosin, Research Council Scale), of the deltoid, infraspinatus, modified Gomori trichrome, PAS, Sudan black B, NADH- pectoralis, finger extensors and interossei. In the lower tetrazolium reductase, succinate dehydrogenase and cyto- extremities, iliopsoas, glutei, ankle and toe extensors were chrome oxidase, ATPase at pH 9.4 and after preincubation all 4/5. The patient could not step on her toes and heels, at pH 4.3 and 4.6. The immunocytological reactions Fig. 1 Myotonic discharges recorded in the right vastus lateralis muscle 123 Myotonia in DNM2-related centronuclear myopathy 551 included dystrophin 1–3, sarcoglycans, merosin, caveolin almost all fibers were of type 1, with a central zone of 3, dysferlin and collagen VI. enzymatic inactivity (Fig. 2). Molecular analysis DNM2 mutation Genomic DNA was extracted from peripheral blood by the Sequencing the entire coding region and exon–intron Puregene kit (Gentra, Minneapolis, USA), according to boundaries of DNM2 revealed a heterozygous c.1106g-a the manufacturer’s instructions. Genomic DNA was used substitution in exon 8, resulting in R369Q change in the as a template for PCR amplification of each of the 21 gene product (Fig. 3). This mutation appears as pathologic exons and exon–intron boundaries of the DNM2 gene. The according to prediction software (polyphen2; score-0.8), reaction was performed in a 25 ll volume containing mutation taster (score-0.999). The substituted amino acid is 10 mM Tris–HCl, pH 8.3, 50 mM KCl, 1.5 mM MgCl2 located in the middle domain (MID) of the dynamin pro- 250 lM dNTPs, 1 lM of each primer, 100 ng of genomic tein. This mutation has been described in CNM cases DNA and 1.25U of AmpliTaq Gold DNA polymerase (Bitoun et al. 2005;Bo¨hm et al. 2012). CLCN1 and SCN4A (Perkin Elmer Applied Biosystem). An initial denaturation mutations were excluded. step of 10 min at 95 °C was carried out to activate the polymerase, followed by 35 cycles of 94 °C15s,55or 60 °C45s,72°C and 45 s and a final elongation of Discussion 10 min at 72 °C. Predicted amplicon sizes were confirmed by agarose gel electrophoresis. The amplified PCR pro- This is the first study to describe the presence of myotonia ducts were purified with the ExoSapIT kit (Amersham in a case of CNM due to a mutation in the dynamin 2 gene. Pharmacia biotech, Amersham, Buckinghanshire, UK), The R369Q mutation (p.Arg369 is changed into glutamine) according to the manufacturer’s instructions, and has been documented in four families (Bitoun et al. 2005; sequenced with fluorescently labeled dedeoxynucleotide Bo¨hm et al. 2012). The severity of the CNM phenotype terminators and an Applied Biosystem 3730A automated was moderate. The age of onset ranged from childhood to sequencer. Sequences were compared with the DNM2 adulthood, and no prominent eye movement deficits were transcript (ENST00000389253), using the DNA variant reported. In all cases, the R369Q mutation was heterozy- analysis Surveyor software, version 3.3 (http://www.soft gous, thus conferring dominant trait of inheritance. Our waregenetics.com). Polymerase chain reaction (PCR) and patient‘s father had an undiagnosed proximal weakness. direct PCR sequencing of the 23 CLCN1 and the 24 We suspect that he had the same disease, which is con- SCN4A exons were performed as described previously gruent with autosomal dominant trait inheritance.