Mutations in the skeletal muscle ryanodine receptor (RYR1) gene are a common cause of neuromuscular disease, ranging from various congenital myopathies to the malignant hyperthermia (MH) susceptibility trait without associated weakness. We sequenced RYR1 in 39 unrelated families with rhabdomyolysis and/or exertional myalgia, frequent presentations in the neuromuscular clinic that often remain unexplained despite extensive investigations. We identified 9 heterozygous RYR1 mutations/variants in 14 families, 5 of them (p.Lys1393Arg; p.Gly2434Arg; p.Thr4288_Ala4290dup; p.Ala4295Val; and p.Arg4737Gln) previously associated with MH. Index cases presented from 3 to 45 years with rhabdomyolysis, with or without exertional myalgia (n=12), or isolated exertional myalgia (n=2). Rhabdomyolysis was commonly triggered by exercise and heat and, less frequently, viral infections, alcohol and drugs. Most cases were normally strong and had no personal MH history. Inconsistent additional features included heat intolerance, and cold-induced muscle stiffness. Muscle biopsies showed mainly subtle changes. Familial RYR1 mutations were confirmed in relatives with similar or no symptoms. These findings suggest that RYR1 mutations may account for a substantial proportion of patients presenting with unexplained rhabdomyolysis and/or exertional myalgia. Associated clinico-pathological features may be subtle and require a high degree of suspicion. Additional family studies are paramount in order to identify potentially MH susceptible relatives.

The congenital myopathies are a group of inherited neuromuscular disorders mainly defined on the basis of characteristic histopathological features. We analysed 66 patients assessed at a single centre over a 5 year period. Of the 54 patients where muscle biopsy was available, 29 (54%) had a core myopathy (Central Core Disease, Multi-minicore Disease), 9 (17%) had Nemaline Myopathy, 7 (13%) had Myotubular/Centronuclear Myopathy, 2 (4%) had Congenital Fibre Type Disproportion, 6 (11%) had isolated type 1 predominance and 1 (2%) had a mixed Core–Rod Myopathy. Of the 44 patients with a genetic diagnosis, RYR1 was mutated in 26 (59%), ACTA1 in 7 (16%), SEPN1 in 7 (16%), MTM1 in 2 (5%), NEB in 1 (2%) and TPM3 in 1 (2%). Clinically, 77% of patients older than 18 months could walk independently. 35% of all patients required ventilatory support and/or enteral feeding. Clinical course was stable or improved in 57/66 (86%) patients, whilst 4 (6%) got worse and 5 (8%) died. These findings indicate that core myopathies are the most common form of congenital myopathies and that more than half can be attributed to RYR1 mutations. The underlying genetic defect remains to be identified in 1/3 of congenital myopathies cases.

Central Core Disease (CCD) and Multi-minicore Disease (MmD) (the "core myopathies") have been mainly associated with mutations in the skeletal muscle ryanodine receptor (RYR1) and the selenoprotein N (SEPN1) gene. A proportion of cases remain unresolved. Mutations in MYH7 encoding the beta myosin heavy chain protein have been implicated in cardiac and, less frequently, skeletal muscle disorders. Here we report four patients from two families with a histopathological diagnosis of MmD, presenting in childhood with slowly progressive muscle weakness, more proximal in Family 1 and more distal in Family 2, and variable degrees of cardiorespiratory impairment evolving later in life. There was also a strong family history of sudden death in the first family. Muscle biopsies obtained in early childhood showed multiple minicores as the most prominent feature. Sequencing of the MYH7 gene revealed heterozygous missense mutations, c.4399C>G; p.Leu1467Val (exon 32) in Family 1 and c.4763G>C; p.Arg1588Pro (exon 34) in Family 2. These findings suggest MYH7 mutations as another cause of a myopathy with multiple cores, in particular if associated with dominant inheritance and cardiac involvement. However, clinical features previously associated with this genetic background, namely a more distal distribution of weakness and an associated cardiomyopathy, may only evolve over time.

The Dubowitz Neuromuscular Centre is the UK National Commissioning Group referral centre for congenital muscular dystrophy (CMD). This retrospective review reports the diagnostic outcome of 214 UK patients referred to the centre for assessment of 'possible CMD' between 2001 and 2008 with a view to commenting on the variety of disorders seen and the relative frequency of CMD subtypes in this patient population. A genetic diagnosis was reached in 53 of 116 patients fulfilling a strict criteria for the diagnosis of CMD. Within this group the most common diagnoses were collagen VI related disorders (19%), dystroglycanopathy (12%) and merosin deficient congenital muscular dystrophy (10%). Among the patients referred as 'possible CMD' that did not meet our inclusion criteria, congenital myopathies and congenital myasthenic syndromes were the most common diagnoses. In this large study on CMD the diagnostic outcomes compared favourably with other CMD population studies, indicating the importance of an integrated clinical and pathological assessment of this group of patients.

Mutations in the skeletal muscle ryanodine receptor (RYR1) gene have been implicated in the malignant hyperthermia (MH) trait and various congenital myopathies, typically of early-childhood onset and associated with cores on muscle biopsy. Here we report three individuals from two families harbouring heterozygous RYR1 missense mutations, presenting with a severe, slowly progressive adult-onset axial myopathy. Two patients (Family 1), a mother and son from Scandinavia, presented with marked lumbar and, to a lesser extent, pelvic girdle weakness. Especially the son complained of deep aching pain in the lower back. On examination they had a waddling gait, lumbar hyperlordosis and a striking inability to bend forward without falling. There was pronounced muscular atrophy of the lumbar spinal erectors. CK was normal in the mother and slightly elevated in the son (486–857 U/L; normal value <400 U/L). Muscle magnetic resonance imaging revealed prominent involvement of the lumbar paraspinal muscles and, less pronounced, pelvic and posterior thigh muscles. The third patient (Family 2) presented in his 8th decade with marked head drop, moderate respiratory impairment and limitation of upward gaze on examination. CK was normal. Cataracts were a feature in all three patients. Quadriceps muscle biopsies in Family 1 showed only minor non-specific changes, whilst increased fibre size variability and cores on oxidative stains were the most prominent findings in the third patient. RYR1 sequencing revealed a heterozygous c.4178A>G; p.Lys1393Arg substitution in Family 1 and a c13513G>C; p.Asp4505His substitution in Family 2, both previously associated with the MH trait. These findings expand the spectrum of RYR1-related myopathies. MH-related RYR1 mutations may present later in life with prominent axial weakness but not always typical histopathological features. The association between RYR1 mutation and cataracts has not been previously reported and warrants further investigation.

of nighttime BiPAP use in 45 patients at an average age of 11.34±4.28 years. Patients at the mildest end of the phenotypic spectrum did not demonstrate a clear pattern of decline in respiratory function. Conclusions: Forced vital capacity is a viable outcome measure for patients at the moderate to severe end of the collagen VI myopathy phenotypic spectrum, a finding which should inform optimal surveillance and clinical trial planning.

King-Denborough syndrome (KDS), first described in 1973, is a rare condition characterised by the triad of dysmorphic features, myopathy, and malignant hyperthermia susceptibility (MHS). Autosomal dominant inheritance with variable expressivity has been reported in several cases. Mutations in the skeletal muscle ryanodine receptor (RYR1) gene have been implicated in a wide range of myopathies such as central core disease (CCD), the malignant hyperthermia (MH) susceptibility trait and one isolated patient with KDS. Here we report clinical, pathologic and genetic features of four unrelated patients with KDS. Patients had a relatively uniform clinical presentation but muscle biopsy findings were highly variable. Heterozygous missense mutations in RYR1 were uncovered in three out of four families, of which one mutation was novel and two have previously been reported in MH. Further RyR1 protein expression studies performed in two families showed marked reduction of the RyR1 protein, indicating the presence of allelic RYR1 mutations not detectable on routine sequencing and potentially explaining marked intrafamilial variability. Our findings support the hypothesis that RYR1 mutations are associated with King-Denborough syndrome but that further genetic heterogeneity is likely.

RYR1 mutations have been associated with a wide spectrum of phenotypes, ranging from the malignant hyperthermia susceptibility (MHS) trait without associated weakness to various congenital myopathies. Whilst muscle pain is a commonly associated feature of many RYR1-related myopathies, exertional myalgia and rhabdomyolysis as the sole presenting feature have only been rarely reported. We report clinical, muscle MR imaging and histopathological findings of 5 patients from 4 families presenting with RYR1-related exertional myalgia and rhabdomyolysis. Patients (2 females, 3 males) are currently between 10 and 52 years of age and presented from between 3 to 15 years of age with recurrent episodes of exertional myalgia and/or rhabdomyolysis. During or immediately after those episodes, serum creatine kinase (CK) levels were markedly increased and ranged from 1551 IU/l to 110200 IU/l. Preceding motor development had been invariably normal. Except one case with mild proximal weakness, patients were normally strong or even particularly sporty with often prominent muscle bulk. Inconsistent additional features included increased tendency to sweat and muscle stiffness prompted by cold. Muscle MR imaging findings ranged from normal to mild increases in proximal signal intensity. Muscle biopsies were normal or showed only mild changes comprising fibre type disproportion and subtle unevenness of oxidative stains. MHS-related heterozygous RYR1 missense mutations p.Gly2434Arg and p.Lys1393Arg were identified in Family 1 and 2, respectively, whilst individuals in two unrelated Afro-Caribbean families carried the same heterozygous p.Thr4288_4290 duplication. These findings suggest that RYR1 mutations ought to be considered in the differential diagnosis of patients presenting with exertional myalgia and/or rhabdomyolysis. Additional clinico-pathological features may be subtle and require a high degree of suspicion and careful assessment.

Poster 001 Mutations in the skeletal muscle ryanodine receptor (RYR1) gene presenting with exertional myalgia and rhabdomyolysis N DLAMINI, NC VOERMANS, S LILLIS, S ABBS, E KAMSTEEG, S AL-SARRAJ, M LAMMENS, F MUNTONI, G DROST, E WRAIGE, B VAN ENGELEN, H JUNGBLUTH 1 Department of Paediatric Neurology, Evelina's Children Hospital, St Thomas' Hospital, London, UK; 2 Department of Neurology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands; 3 GSTS Pathology, Guy's Hospital, London, UK; 4 Department of Human Genetics, University Medical Centre St Radboud, Nijmegen, The Netherlands; 5 Department of Neuropathology, King's College, London, UK; 6 Department of Pathology, University Medical Centre St Radboud, Nijmegen, The Netherlands; 7 Dubowitz Neuromuscular Centre, Great Ormond Street Hospital for Children, London, UK; 8 Clinical Neuroscience Division, IOP, King's College, London, UK

OBJECTIVE:To assess the clinical course and genotype-phenotype correlations in patients with selenoprotein-related myopathy (SEPN1-RM) due to selenoprotein N1 gene (SEPN1) mutations for a retrospective cross-sectional study. METHODS:Forty-one patients aged 1-60 years were included. Clinical data including scoliosis, respiratory function, and growth measurements were collected by case note review. RESULTS:Mean age at onset was 2.7 years, ranging from birth to the second decade of life. All but 2 remained independently ambulant: one lost ambulation at age 5 years and another in his late 50s. The mean age of starting nocturnal noninvasive ventilation (NIV) was 13.9 years. One child required full-time NIV at the age of 1 year while in 2 cases NIV was started at 33 years. Two patients died from respiratory failure at the age of 10 and 22 years, respectively. The mean age at scoliosis onset was 10 years, in most cases preceded by rigidity of the spine. Fourteen patients had successful spinal surgery (mean age 13.9 years). Twenty-one were underweight; however, overt feeding difficulties were not a feature. CONCLUSIONS:This study describes the largest population affected by SEPN1-RM reported so far. Our findings show that the spectrum of severity is wider than previously reported. Respiratory insufficiency generally develops by 14 years but may occur as early as in infancy or not until the fourth decade. Motor abilities remain essentially static over time even in patients with early presentation. Most adult patients remain ambulant and fully employed.

Muscle pathology in cases with Selenoprotein N1 (SEPN1) mutations includes dystrophic changes, multiminicores, Mallory-body like inclusions, or only congenital fibre-type disproportion (CFTP). RYR1 mutations can also give rise to cores of varying size and CFTP, and cores can be associated with several other defective genes. We have reviewed the muscle pathology of 21 cases with SEPN1 mutations to identify features that may direct molecular analysis. All cases had mild to severe variation in fibre size and several cases had mild to moderate increased connective tissue (9 cases) and/ or fat (6 cases). Four of these cases also showed basophilic fibres. Multiminicores or unevenness of oxidative enzyme stains in both fibre types was present in 15 cases (71%). All cases showed preservation of two fibre types but predominance of type I fibre was present in a few; one exceptional case had predominance of type 2 fibres. One case was reported to show Mallory-like bodies. Immunolabelling of neonatal myosin showed diffusely distributed small and large positive fibres in 4 cases (results available in 5 cases only), in contrast to the very small fibres seen in cases with RYR1 mutation (s). Co-expression of fast and slow myosin in some fibres was seen in all these 5 cases. We confirm that the most common features associated with SEPN1 mutations are variation in fibre size, multiminicores or unevenness of oxidative enzyme stain with preservation of a two fibre type pattern. CFTP without any structural change was not observed in our 21 cases and dystrophic changes were rare. Finding of expression of neonatal myosin in scattered small and large positive fibres may be indicative of SEPN1 mutations but further studies are required to confirm this. A combination of clinical- pathological findings is essential for directing molecular analysis.

Congenital myopathies (CM) are a rare group of neuromuscular disorders, mainly defined on the basis of morphological features. The frequency of single entities of CM is still unsolved. Our aim was to study retrospectively clinical, histological and molecular data of a wide population of patients affected by CM referred to the Dubowitz Neuromuscular Centre in UK. We included 66 patients who were physically assessed at out Centre between 1.1.2005 and 31.12.2009, in whom we arrived to a clinical, histological and/or molecular diagnosis of CM. Muscle biopsy was available in 54 patients and morphological analysis revealed a core myopathy in 31 (57.4%) patients, nemaline myopathy in 9 (16.7%), myotubular/centronuclear myopathy in 7 (13%), congenital fibre-type disproportion in 2 (3.7%), rod-core myopathy in 1 (1.8%); 4 (7.4%) patients had fibre type I predominance, and involvement of one of the genes responsible for CM was confirmed. The following genes were systematically studied: RYR1, SEPN1, ACTA1, MTM1, NEB, TPM3, BIN1, DNM2, MYH7, CFL2. All genes were studied by direct sequencing with the exception of NEB in which we only studied the common exon 55 deletion. To date, a final molecular diagnosis was achieved in 44 (66.7%) patients. RYR1 gene was mutated in 26/44 (59.1%) patients, ACTA1 in 7 (15.9%), SEPN1 in 7 (15.9%), MTM1 in 2 (4.5%), NEB in 1 (2.3) and TPM3 in 1 (2.3%). The mean age at onset in our patients was 0.8 ± 1.6 years (range 0–7); independent walking was reached in 43 (65.2%) patients. Fifteen (22.7%) patients required non invasive ventilation at mean age of 2.4 ± 3.4 years and 14 (21.2%) had gastrostomy at mean age of 0.8 ± 0.3 years. The clinical course was stable or improved in 56 (84.8%) patients, while 5 (7.6%) patients died. In conclusion, core myopathy was the most frequent CM in our population and RYR1 the gene more frequently involved.

A new entity of congenital myopathy in Japanese and Turkish children caused by autosomal recessive mutations in the gene encoding for choline kinase beta (CHKB) was recently described by Nishino et al. We describe the clinical features of three caucasian British patients with the condition, confirmed by genetic analysis. We found a spectrum of severity from severe: presenting with learning difficulty, autism, ichthyosis and early death from cardiomyopathy to a milder phenotype in a female patient who is now in her early twenties. She presented with progressive limb girdle weakness from early childhood, calf hypertrophy, myalgia, learning difficulties and a mildly elevated serum CK activity (600 U/l), The third patient had intermediate features with a small discrete area of linear ichthyosis on the upper trunk. Brain imaging was normal, brain magnetic resonance spectroscopy (MRS) performed in the adult patient, was abnormal. In all three patients muscle biopsy features included either myopathic or dystrophic features, uneven COX staining and giant mitochondria on electron microscopy. Analysis of CHKB activity in skeletal muscle tissue of the patients was severely reduced. Overall it seems that the clinical spectrum of CHKB deficiency is fairly broad and can resemble patients with congenital myopathy, congenital muscular dystrophy and also limb girdle muscular dystrophy. The clinical presentation in two of our patients was not dissimilar to Chanarin–Dorfman syndrome (Neutral lipid storage disorder) and thus mutations in CHKB should also be considered as a differential diagnosis for this condition.