G.P.139

842

Abstracts / Neuromuscular Disorders 24 (2014) 791–924

populations of patients are needed. We included patients referred to Carlo Besta Neurological Institute molecular laboratory with a clinical diagnosis of periodic paralysis or nondystrophic myotonia and mutated in CLCN1, SCN4A, KCNJ2 or CACNA1S. We investigated 301 patients, among which 195 (64.3%) patients mutated in CLCN1 gene, 74 (24.6%) in SCN4A, 28 (9.3%) in CACNA1S and 4 (1.3%) in KCNJ2. We found 22 novel mutations: 8 in CLCN1 gene, 13 in SCN4A and 1 in CACNA1S. All the mutations detected in SCN4A, CACNA1S and KCNJ2 genes were missense, except for an unreported 9-nucleotide deletion in SCN4A. On the contrary CLCN1mutations were missense in 131/195 (67.2%) patients and remaining cases showed nonsense, splice site or deletion mutations. Our study confirms genetic heterogeneity of muscle channelopathies, although a relatively small number of mutations is responsible for most of the cases. http://dx.doi:10.1016/j.nmd.2014.06.166

G.P.137 Functional study of five new CLC-1 mutations causing myotonia congenita in Italian families P. Imbrici 1, J.F. Desaphy 1, R. Brugnoni 2, L. Colleoni 2, E. Canioni 2, D. Kapetis 2, C. Altamura 1, P. Bernasconi 2, L. Morandi 2, L. Maggi 2, R. Mantegazza 2, D. Conte 1 1 Universita` degli Studi di Bari, Bari, Italy; 2 Fondazione Istituto Neurologico, Milano, Italy Myotonia congenita is an inherited disease characterized by impaired muscle relaxation after contraction, resulting in muscle stiffness. It is caused by loss-of-function mutations of the muscle ClC-1 chloride channel. We report the functional characterization of five novel mutations found in patients with recessive and dominant myotonia congenita, selected among the largest cohort of Italian families reported to date, on the basis of the associated clinical phenotype and position in the protein 3D-structure. The mutations F484L, L198P and L520P resides within the channel pore and are inherited in a dominant manner. The mutations V640G and L628P occur in the C-terminal domain and show a recessive inheritance. Recombinant hClC-1 channel mutants were expressed in a mammalian cell line for patch-clamp studies of chloride current properties. The mutant channels F484L, L198P and V640G show a large current reduction at every tested potential. In addition, the mutations F484L and L198P induce a dramatic shift of activation voltage-dependence toward more positive potentials, resulting in nearly zero chloride current within physiological voltage range. These effects likely contribute to impaired muscle repolarization and explain the myotonia. Further experiments are required to clarify the dominant inheritance for mutations located outside the common hot-spot for dominant genetic variants, to address the mechanism of ATP modulation for the mutations close to the ATP binding sites, and to clarify genotype-phenotype correlations. Pharmacogenetics studies are also in progress. http://dx.doi:10.1016/j.nmd.2014.06.167

G.P.138 Late-onset non-thymomatous generalized myasthenia gravis S. Yildiz-Celik, H. Durmus, M. Hajibehzad, V. Yilmaz, P. Oflazer-Serdaroglu, Y. Parman, G. Saruhan-Direskeneli, F. Deyemeer Istanbul Medical Faculty, Istanbul University, Istanbul, Turkey Findings in recent epidemiological studies have implied that the frequency of myasthenia gravis (MG) may be increasing in the elderly population. Published studies of late-onset MG have disclosed some of

its characteristics: males are more frequently affected, the thymus is more likely to be involuted, there is a different HLA profile and antistriatal muscle antibodies against titin/ryanodine receptors may be present. In our MG database, there were 95 generalized nonthymomatous MG patients with disease onset P50 years who first presented to our outpatient clinic during the 10 years between 2001 and 2010 and who were followed for at least 3 years. All patients were contacted by phone calls or letters. There was a marked male preponderance with male to female ratio of 1.7:1. Onset was with predominantly ocular symptoms (62%), followed by bulbar symptoms (23%) and weakness in the extremities (11%); two patients had neck weakness and 4 had mixed onset symptoms. Anti-acetylcholine receptor antibodies (AChR Ab) were present in 84%, 5% were anti-MuSK Ab positive and 11 % were double negative. Sixty-two percent had anti-titin antibodies. The disease was mild (MGFA 2) in approximately half of the patients (47%) while 6% were intubated. Fifty-seven percent (including all of the patients with MuSK MG) had MGFA postintervention status of complete stable remission/pharmacological remission/minimal manifestations at the last visit. A further 28 % were improved. The combination of prednisolone and azathioprine appeared to be superior to these agents used alone. In 15 mildly affected patients in whom azathioprine was combined with low dose prednisolone (<30 mg/day), 73% had pharmacological remission/minimal manifestations. Fifteen patients had thymectomy, but its effect could not be evaluated because of concomitant immunosuppressives. The thymus showed hyperplasia in only one-third. In this study group, LOMG appears to be a fairly benign disorder with good prognosis. http://dx.doi:10.1016/j.nmd.2014.06.168

G.P.139 Congenital myasthenic syndrome due to novel choline acetyltransferase (ChAT) gene mutations in Kadazandusun family from Borneo J.S. Tan, T. Ambang, A. Ahmad-Annuar, K.T. Wong, K.J. Goh University of Malaya, Kuala Lumpur, Malaysia Pathogenic mutations of the choline acetyltransferase (ChAT) gene alters its function and causes reduced synthesis of acetylcholine and its depletion in synaptic vesicles. This results in a rare presynaptic form of congenital myasthenic syndrome which presents at birth or in infancy characterised by apnoeic attacks. We present Kadazandusun family, an ethnic group native to Sabah, in north Borneo, with ChAT deficiency in which 5 of 6 siblings of non-consanguineous parents were affected. 2 died in their infancy from apnoeic atatacks while another sibling died at the age of 12 years from a severe apnoeic episode after an intercurrent infection. We reviewed 2 brothers, the eldest and the 4th at 24 and 18 years of age respectively, although both had presented in infancy with bilateral ptosis and limb weakness. The elder brother had episodes of apnoea and weakness on exposure to cold well water in their village. A congenital myasthenic syndrome was suspected and both brothers were treated on pyridostigmine after positive Tensilon tests and negative acetylcholine receptor antibody tests. On review, both had muscle weakness after moderate to severe exertion and repetitive nerve stimulation test of the abductor digiti minimi, which was normal at rest, showed sustained decremental response after prolonged 5 min stimulation at 10 Hz. Screening of the ChAT gene showed compound heterozygous mutation in both brothers, c.1069G>C and c.2263_2265delTCT in exons 6 and 15 respectively. Each parent was heterozygous for one of the mutations, which were not seen in any of 50 normal controls obtained from the native population of Sabah. In summary, we present a Kadazandusun family with ChAT deficiency congenital myasthenic syndrome, in which, 3 affected siblings died from apnoeic episodes, while another 2 survived to adulthood. This variable

Abstracts / Neuromuscular Disorders 24 (2014) 791–924 severity could be attributed to treatment with pyridostigmine as well as recognised improvement with age in this condition. http://dx.doi:10.1016/j.nmd.2014.06.169

G.P.140 A novel missense mutation in the AGRN gene causing congenital myasthenic syndrome mimicking neck myopathy M. Karakaya 1, O. Ceyhan-Birsoy 2, A.H. Beggs 2, H. Topaloglu 1 1 Hacettepe University, Ankara, Turkey; 2 Boston Children’s Hospital, Harvard Medical School, The Manton Center for Orphan Disease Research, Boston, USA Congenital myasthenic syndromes (CMS) are inherited diseases of the neuromuscular junction (NMJ), causing muscle weakness worsened by physical exertion. Mutations in agrin were shown to cause CMS and affect synapse function. Here we describe a 17-month-old Turkish infant male from a consanguineous family who presented with neck weakness and mild hypotonia. He was able to stand and walk unsupported a few steps by 1-year of age. Over the following year, he was followed with a provisional clinical diagnosis of congenital myopathy or neck myopathy. During his second visit at 36-months of age, he presented with ptosis and restrictive eye movements deteriorating during the day. Electromyographic study revealed an NMJ problem, such that 10–30% amplitude decline was observed at 3.5 Hz stimulation whereas no decline was observed at 20 Hz stimulation. Screens for acetylcholine receptor antibodies and MuSK antibodies were negative. His symptoms improved after pyridostigmine treatment, but he still develops mild ptosis during the day. His initial presentation with isolated neck weakness sparing the eyes was not consistent with typical presentation of CMS. Thus, we listed LMNA or SEPN1-related myopathies in the differential diagnosis. We performed whole exome sequencing (WES) on the patient’s DNA. On bioinformatic analysis, he was identified to carry a homozygous point mutation c.5023G>A in the AGRN gene resulting in a missense variant (p.Gly1675Ser).This mutation was not present in current databases.Further studies are proceeding to reveal the in vitro effects of this mutation on functional assays and to ensure the genotypephenotype correlation between this novel mutation and unusual disease presentation.With this report we emphasize the importance of early diagnosis for initiation of treatment of CMS in patients with provisional clinical diagnosis of neck myopathy.This study also emphasizes the significance of WES as a diagnostic tool to expedite the diagnosis of NMDs with unclear presentations. http://dx.doi:10.1016/j.nmd.2014.06.170

G.P.141 Dpagt1 mutation: Limb-girdle congenital myasthenic syndrome due to glycosylation defect _ ¨ ncel 1, A. To¨pf 2, T. Evangelista 2, B. Konusßkan 1, B. Talim 1, I. O A. Abicht 2, H. Lochmu¨ller 2, H. Topaloglu 1 1 Hacettepe Children’s Hospital, Ankara, Turkey; 2 Institute of Genetic Medicine, Newcastle University, Newcastle, UK Congenital myasthenic syndromes (CMSs) are heterogeneous genetic disorders that result from impaired signal transmission at the neuromuscular junction (NMJ). Congenital disorders of glycosylation (CDG) are a challenging group of diseases affecting different organs in particular the central nervous system and the skeletal muscle. Only recently CDG have been implicated in some forms of post-synaptic autosomal recessive CMS. The protein encoded by the DPAGT1 gene is an enzyme that catalyzes the first step in the dolichol-linked oligosaccharide pathway for glycoprotein biosynthesis. Mutations in

843

DPAGT1 were described in patients with CMS and tubular aggregates on muscle biopsy. We report a 16 year old young man, first child of a consanguineous family, who presented with walking difficultywith onset by the age of 3 year. The motor milestones were slightly delayed. There was speech difficulty which fluctuated during the day. On examination, he had generalized muscle weakness with proximal groups being more affected, excessive lordosis, waddling gait, and contractures of the Achilles tendons. There was no bulbar or extra-ocular muscle involvement. He had a mild intellectual disability with an IQ score of 50–55. Tensilon test was positive. Electromyography revealed decrementing response to repetitive nerve stimulation. He responded well to pyridostigmine, 3,4-diaminopyridine and salbutamol treatment. We carried out whole exome sequencing and identified a novel homozygous DPAGT1 mutation (c.509A>T). The non-synonymous change (p.Tyr170Phe) is predicted to be deleterious by in silico analysis and affects an aminoacid residue that is highly conserved across species. In conclusion we report a novel mutation on the DPAGT1 gene responsible for a form of “limb-girdle CMS”. Comparing with the previously reported cases this family has mental retardation as an unusual feature and a good response to a combined treatment with pyridostigmine and 3,4-diaminopyridine. http://dx.doi:10.1016/j.nmd.2014.06.171

EDMD LAMIN A/C EMERIN FHL1 G.P.142 A new EMD gene missense mutation in exon 1 leads to absence of emerin and is responsible for X-linked dilated cardiomyopathy with conduction defects and arrhythmias and almost elusive skeletal muscle features R. Ben Yaou 1, M. Gerard 2, K. Chami 3, A. Sehier 2, A. Belin 4, F. Labombarda 4, P. Richard 5, G. Bonne 6, F. Leturcq 7, F. Chapon 4 1 Paris-Est Neuromuscular Center, UPMC-Paris 6, CNRS, FRE 3617, Paris, France; 2 CHU Cle´menceau, Caen, France; 3 CH Coˆte fleurie, Honfleur, France; 4 CHU Cote de Nacre, Caen, France; 5 AP-HP, GH Pitie-Salpetriere, Paris, France; 6 UF Cardioge´ne´tique et Myoge´ne´tique, Inserm, U974, UPMC-Paris 6, CNRS, FRE 3617, Paris, France; 7 AP-HP, GH Cochin, Paris, France Mutations in the EMD gene, encoding emerin, lead to X-linked Emery-Dreifuss muscular dystrophy (EDMD). Although always associated with EDMD, an almost exclusive cardiac involvement was found in exceptional patients carrying EMD gene mutations. We here report 2 brothers belonging to a family where 9 affected male subjects developed dilated cardiomyopathy (DCM) with conduction defects and arrhythmias. The oldest brother of 53 years developed DCM since 49 years and requiring implantable cardioverter defibrillator (ICD) implantation. He subsequently developed atrio-ventricular and ventricular conduction defects as well as ventricular arrhythmias at 52 years that required ICD upgrading and additional pacemaker implantation. His youngest brother aged 45 years was also affected. The family history showed several affected members: a third brother who died after cardiac transplantation at 38 years, a fourth brother who died suddenly at 50 years, two maternal uncles and cousins died in their 5th or 6th decades among them 2 were diagnosed as arrhythmogenic right ventricular dysplasia. An X-linked mode of inheritance was therefore suspected and DMD gene analysis did not show any exonic deletion or duplication or exon 1 point mutation. Further neurological assessment of the oldest brother showed neither muscle weakness nor joint contractures whereas hands and legs were slightly hypotrophic. CPK were at normal level and needle electromyography examination showed normal pattern. Deltoid muscle biopsy was normal as were protein immunohistochemical studies including dystrophin, desmin, myotilin