Acute oral toxicity and tissue residues of saxitoxin in the mallard (Anas platyrhynchos).

Since 2014, widespread, annual mortality events involving multiple species of seabirds have occurred in the Gulf of Alaska, Bering Sea, and Chukchi Sea. Among these die-offs, emaciation was a common finding with starvation often identified as the cause of death. However, saxitoxin (STX) was detected in many carcasses, indicating exposure of these seabirds to STX in the marine environment. Few data are available that describe the effects of STX in birds, thus presenting challenges for determining its contributions to specific mortality events. To address these knowledge gaps, we conducted an acute oral toxicity trial in mallards (Anas platyrhynchos), a common laboratory avian model, using an up-and-down method to estimate the median lethal dose (LD50) for STX. Using an enzyme-linked immunosorbent assay (ELISA), we tested select tissues from all birds and feces from those individuals that survived initial dosing. Samples with an ELISA result that exceeded approximately 10 µg 100 g-1 STX and randomly selected ELISA negative samples were further tested by high-performance liquid chromatography (HPLC). Tissues collected from mallards were also examined grossly at necropsy and then later by microscopy to identify lesions attributable to STX. The estimated LD50 was 167 µg kg-1 (95% CI = 69-275 µg kg-1). Saxitoxin was detected in fecal samples of all mallards tested for up to 48 h after dosing and at the end of the sampling period (7 d) in three birds. In those individuals that died or were euthanized <2 h after dosing, STX was readily detected throughout the gastrointestinal tract but only infrequently in heart, kidney, liver, lung, and breast muscle. No gross or microscopic lesions were observed that could be attributable to STX exposure. Given its acute toxicity, limited detectability, and frequent occurrence in the Alaska marine environment, additional research on STX in seabirds is warranted.

Extreme mortality and reproductive failure of common murres resulting from the northeast Pacific marine heatwave of 2014-2016.

About 62,000 dead or dying common murres (Uria aalge), the trophically dominant fish-eating seabird of the North Pacific, washed ashore between summer 2015 and spring 2016 on beaches from California to Alaska. Most birds were severely emaciated and, so far, no evidence for anything other than starvation was found to explain this mass mortality. Three-quarters of murres were found in the Gulf of Alaska and the remainder along the West Coast. Studies show that only a fraction of birds that die at sea typically wash ashore, and we estimate that total mortality approached 1 million birds. About two-thirds of murres killed were adults, a substantial blow to breeding populations. Additionally, 22 complete reproductive failures were observed at multiple colonies region-wide during (2015) and after (2016-2017) the mass mortality event. Die-offs and breeding failures occur sporadically in murres, but the magnitude, duration and spatial extent of this die-off, associated with multi-colony and multi-year reproductive failures, is unprecedented and astonishing. These events co-occurred with the most powerful marine heatwave on record that persisted through 2014-2016 and created an enormous volume of ocean water (the "Blob") from California to Alaska with temperatures that exceeded average by 2-3 standard deviations. Other studies indicate that this prolonged heatwave reduced phytoplankton biomass and restructured zooplankton communities in favor of lower-calorie species, while it simultaneously increased metabolically driven food demands of ectothermic forage fish. In response, forage fish quality and quantity diminished. Similarly, large ectothermic groundfish were thought to have increased their demand for forage fish, resulting in greater top-predator demands for diminished forage fish resources. We hypothesize that these bottom-up and top-down forces created an "ectothermic vise" on forage species leading to their system-wide scarcity and resulting in mass mortality of murres and many other fish, bird and mammal species in the region during 2014-2017.

Mercury concentrations in multiple tissues of Kittlitz's murrelets (Brachyramphus brevirostris).

Mercury (Hg) is a non-essential, toxic metal that is distributed worldwide. Mercury biomagnifies in food webs and can threaten the health of top predators such as seabirds. The Kittlitz's murrelet (Brachyramphus brevirostris) is a seabird endemic to Alaska and the Russian Far East and is a species of conservation concern in the region. We determined Hg concentrations in eggshells, guano, blood, and feathers of Kittlitz's murrelets sampled from four locations in Alaska. Mercury concentrations in eggshells, guano, and blood were low compared to other seabird species. Mean Hg concentrations of breast feathers from Adak Island and Glacier Bay were significantly greater than those from Agattu Island or Icy Bay. Two Kittlitz's murrelets at Glacier Bay and one Kittlitz's murrelet at Adak Island had Hg concentrations above those associated with impaired reproduction in other bird species, and may merit further investigation as a potential threat to individuals and populations.

RYR1-related congenital myopathy with fatigable weakness, responding to pyridostigimine.

The spectrum of RYR1 mutation associated disease encompasses congenital myopathies, exercise induced rhabdomyolysis, malignant hyperthermia susceptibility and King-Denborough syndrome. We report the clinical phenotype of two siblings who presented in infancy with hypotonia and striking fatigable ptosis. Their response to pyridostigimine was striking, but genetic screening for congenital myasthenic syndromes was negative, prompting further evaluation. Muscle MRI was abnormal with a selective pattern of involvement evocative of RYR1-related myopathy. This directed sequencing of the RYR1 gene, which revealed two heterozygous c.6721C>T (p.Arg2241X) nonsense mutations and novel c.8888T>C (p.Leu2963Pro) mutations in both siblings. These cases broaden the RYR1-related disease spectrum to include a myasthenic-like phenotype, including partial response to pyridostigimine. RYR1-related myopathy should be considered in the presence of fatigable weakness especially if muscle imaging demonstrates structural abnormalities. Single fibre electromyography can also be helpful in cases like this.

Mercury concentrations in breast feathers of three upper trophic level marine predators from the western Aleutian Islands, Alaska.

Mercury (Hg) is a toxic element distributed globally through atmospheric transport. Agattu Island, located in the western Aleutian Islands, Alaska, has no history of point-sources of Hg contamination. We provide baseline levels of total mercury (THg) concentrations in breast feathers of three birds that breed on the island. Geometric mean THg concentrations in feathers of fork-tailed storm-petrels (Oceanodroma furcata; 6703 ± 1635, ng/g fresh weight [fw]) were higher than all other species, including snowy owl (Bubo scandiacus; 2105 ± 1631, ng/g fw), a raptor with a diet composed largely of storm-petrels at Agattu Island. There were no significant differences in mean THg concentrations of breast feathers among adult Kittlitz's murrelet (Brachyramphus brevirostris; 1658 ± 1276, ng/g fw) and chicks (1475 ± 671, ng/g fw) and snowy owls. The observed THg concentrations in fork-tailed storm-petrel feathers emphasizes the need for further study of Hg pollution in the western Aleutian Islands.

Outcome of children with acetylcholine receptor (AChR) antibody positive juvenile myasthenia gravis following thymectomy.

Most evidence supporting the benefit of thymectomy in juvenile myasthenia gravis (JMG) is extrapolated from adult studies, with only little data concerning paediatric populations. Here we evaluate the outcome of children with generalized JMG who underwent thymectomy between 1996 and 2010 at 2 tertiary paediatric neurology referral centres in the United Kingdom. Twenty patients (15 female, 5 male), aged 13months to 15.5years (median 10.4years) at disease onset, were identified. Prior to thymectomy, disease severity was graded as IIb in 3, III in 11, and IV in 6 patients according to the Osserman classification. All demonstrated positive anti-acetylcholine receptor (AChR) antibody titres. All patients received pyridostigmine and 14 received additional steroid therapy. Transternal thymectomy was performed at the age of 2.7-16.6years (median 11.1years). At the last follow-up (10months to 10.9years, median 2.7years, after thymectomy), the majority of children demonstrated substantial improvement, although some had required additional immune-modulatory therapies. About one third achieved complete remission. The postoperative morbidity was low. No benefit was observed in one patient with thymoma. We conclude that thymectomy should be considered as a treatment option early in the course of generalised AChR antibody-positive JMG.

Congenital myopathies--clinical features and frequency of individual subtypes diagnosed over a 5-year period in the United Kingdom.

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.

Relative frequency of congenital muscular dystrophy subtypes: analysis of the UK diagnostic service 2001-2008.

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.

Congenital fibre type disproportion associated with mutations in the tropomyosin 3 (TPM3) gene mimicking congenital myasthenia.

Congenital myopathy with fibre type disproportion (CFTD) has been associated with mutations in ACTA1, SEPN1, RYR1 and TPM3 genes. We report the clinico-pathological and electrophysiological features of 2 unrelated cases with heterozygous TPM3 mutation. Case 1 is a 19-year-old lady who presented with motor delay in infancy, respiratory failure in early teens requiring non-invasive ventilation despite being ambulant, ptosis, axial more than proximal weakness and scoliosis. Case 2 is a 7-year-old boy with hypotonia, feeding difficulties, motor delay and scoliosis, also requiring non-invasive ventilation while ambulant. Muscle biopsies in both cases showed fibre type disproportion. Muscle MRI (Case 1) showed mild uniformly increased interstitial tissue in and around the muscles. Sequencing of TPM3 in case 1 revealed a previously described heterozygous c.503G > A(pArg168His) missense variant in exon 5 and a novel heterozygous missense mutation c.521A > C(pGlu174Ala), also in exon 5, in case 2. A mild abnormality in the single fibre EMG was documented on electrophysiology in both cases. These cases highlight the neuromuscular transmission defect in CFTD secondary to TPM3 mutations.

Natural history of Ullrich congenital muscular dystrophy.

OBJECTIVE: To describe the course, complications, and prognosis of Ullrich congenital muscular dystrophy (UCMD), with special reference to life-changing events, including loss of ambulation, respiratory insufficiency, and death. METHODS: Review of the case notes of 13 patients with UCMD, aged 15 years or older at last visit, followed up at a tertiary neuromuscular centre, London, UK, from 1977 to 2007. Data collected were age at onset of symptoms, presenting symptoms, mobility, contractures, scoliosis, skin abnormalities, respiratory function, and feeding difficulties. RESULTS: The mean age at onset of symptoms was 12 months (SD 14 months). Eight patients (61.5%) acquired independent ambulation at a mean age of 1.7 years (SD 0.8 years). Nine patients (69.2%) became constant wheelchair users at a mean age of 11.1 years (SD 4.8 years). Three patients continued to ambulate indoors with assistance. Forced vital capacity (FVC) values were abnormal in all patients from age 6 years. The mean FVC (% predicted) declined at a mean rate of 2.6% (SD 4.1%) yearly. Nine patients (69.2%) started noninvasive ventilation at a mean age of 14.3 years (SD 5.0 years). Two patients died of respiratory insufficiency. CONCLUSION: In Ullrich congenital muscular dystrophy (UCMD), the decline in motor and respiratory functions is more rapid in the first decade of life. The deterioration is invariable, but not always correlated with age or severity at presentation. This information should be of help to better anticipate the difficulties encountered by patients with UCMD and in planning future therapeutic trials in this condition.

Interfamilial phenotypic heterogeneity in SMARD1.

Spinal muscular atrophy with respiratory distress (SMARD1: mu-binding protein 2 gene mutation) is characterised by low birth weight, progressive distal limb weakness, diaphragmatic paralysis and subsequent respiratory failure manifesting before 13 months of age. Our case report illustrates marked phenotype variability in two siblings with an identical genetic mutation of SMARD1, one of whom died of fulminant respiratory failure aged 6 months, whereas the other shows limb weakness but, only mild sleep hypoventilation aged 12 years. This suggests other compensatory mechanisms may play a role in modifying SMARD1; broadening our perception of phenotype. Therefore, SMARD1 phenotype should be considered in cases of atypical spinal muscular atrophy even in the absence of overt diaphragmatic weakness.

Congenital myasthenic syndromes in childhood: diagnostic and management challenges.

The Congenital Myasthenic Syndromes (CMS), a group of heterogeneous genetic disorders of neuromuscular transmission, are often misdiagnosed as congenital muscular dystrophy (CMD) or myopathies and present particular management problems. We present our experience of 46 children with CMS, referred to us between 1992-2007 with provisional diagnoses of congenital myopathy (22/46), CMS or limb-girdle myasthenia (9/46), central hypotonia or neurometabolic disease (5/46), myasthenia gravis (4/46), limb-girdle or congenital muscular dystrophy (4/46) and SMA (2/46). Diagnosis was often considerably delayed (up to 18y4 m), despite the early symptoms in most cases. Diagnostic clues in the neonates were feeding difficulties (29/46), hypotonia with or without limb weakness (21/46), ptosis (19/46), respiratory insufficiency (12/46), contractures (4/46) and stridor (6/46). Twenty-five children had delayed motor milestones. Fatigability developed in 43 and a variable degree of ptosis was eventually present in 40. Over the period of the study, the mainstay of EMG diagnosis evolved from repetitive nerve stimulation to stimulation single fibre EMG. The patients were studied by several different operators. 66 EMGs were performed in 40 children, 29 showed a neuromuscular junction abnormality, 7 were myopathic, 2 had possible neurogenic changes and 28 were normal or inconclusive. A repetitive CMAP was detected in only one of seven children with a COLQ mutation and neither of the two children with Slow Channel Syndrome mutations. Mutations have been identified so far in 32/46 children: 10 RAPSN, 7 COLQ, 6 CHRNE, 7 DOK7, 1 CHRNA1 and 1 CHAT. 24 of 25 muscle biopsies showed myopathic changes with fibre size variation; 14 had type-1 fibre predominance. Three cases showed small type-1 fibres resembling fibre type disproportion, and four showed core-like lesions. No specific myopathic features were associated with any of the genes. Twenty children responded to Pyridostigmine treatment alone, 11 to Pyridostigmine with either 3, 4 DAP or Ephedrine and five to Ephedrine alone. Twenty one children required acute or chronic respiratory support, with tracheostomy in 4 and nocturnal or emergency non-invasive ventilation in 9. Eight children had gastrostomy. Another 11 were underweight for height indicative of failure to thrive and required dietetic input. A high index of clinical suspicion, repeat EMG by an experienced electromyographer and, if necessary, a therapeutic trial of Pyridostigmine facilitates the diagnosis of CMS with subsequent molecular genetic confirmation. This guides rational therapy and multidisciplinary management, which may be crucial for survival, particularly in pedigrees where previous deaths have occurred in infancy.

Minicore myopathy with ophthalmoplegia caused by mutations in the ryanodine receptor type 1 gene.

BACKGROUND: Minicore myopathy (multi-minicore disease [MmD]) is a congenital myopathy characterized by multifocal areas with loss of oxidative activity on muscle biopsy. MmD is clinically heterogeneous and distinct phenotypes have been associated with recessive mutations in either the selenoprotein N (SEPN1) or the skeletal muscle ryanodine receptor (RYR1) gene, also implicated in central core disease and malignant hyperthermia. External ophthalmoplegia is an additional finding in a subset of patients with MmD. OBJECTIVE: To clinically and genetically examine families with MmD and external ophthalmoplegia. METHODS: The authors investigated 11 affected individuals from 5 unrelated families. Clinical, histopathologic, and imaging studies were performed and RYR1 haplotyping and mutational analysis were carried out. RESULTS: All patients had multiple cores involving the entire fiber diameter on longitudinal sections. Weakness and wasting in the shoulder girdle, scoliosis, moderate respiratory impairment, and feeding difficulties were prominent. In contrast to SEPN1-related myopathies, soleus was more severely affected than gastrocnemius on muscle MRI. Haplotyping suggested linkage to the RYR1 locus in informative families and mutational screening revealed four novel RYR1 mutations in three unrelated families; in addition, functional haploinsufficiency was found in one allele of two recessive cases. CONCLUSION: These findings expand the phenotypic spectrum associated with mutations in the skeletal muscle ryanodine receptor (RYR1) gene. Recessive mutations of domains commonly affected in malignant hyperthermia appear to be particularly prevalent in multi-minicore disease with external ophthalmoplegia and might suggest a different pathomechanism from that involved in central core disease.

Analysis of an adult Duchenne muscular dystrophy population.

BACKGROUND: Advances in management have led to increasing numbers of patients with Duchenne muscular dystrophy (DMD) reaching adulthood. Older patients with DMD are necessarily severely disabled, and their management presents particular practical issues. AIM: To review the management of a late adolescent and adult DMD population, and to identify areas in which the present service provisions may be inadequate to their needs. DESIGN: Retrospective review. METHODS: We studied 25 patients with DMD referred to an adult neuromuscular clinic over a 7-year period. Clinical details were obtained retrospectively, from case notes or direct observations. RESULTS: There were 24 males and one symptomatic female carrier. Nine patients died during the observation period. There was no significant correlation between age of wheelchair confinement and age of death. Sixteen patients received non-invasive positive pressure support. Twelve attended mainstream schools and 12, residential special schools. All the patients lived at home for some or all of the time, when their main carers were either one or both of the parents. The most striking difficulties were with the provision of practical aids, including appropriate hoists and belts, feeding and toileting aids, and the conversion of accommodation. Patients rarely wished to discuss the later stages of their disease, and death was often more precipitate than expected. Death usually occurred outside hospital and the final cause was often difficult to establish. DISCUSSION: Adult patients with DMD develop progressive impairment, due to respiratory, orthopaedic and general medical factors. However, the particular areas of difficulty in this study often reflected inadequate and poorly directed social and medical support, illustrating the need for improvements in the structure, co-ordination and breadth of rehabilitation services for adult patients with DMD.

Bladder dysfunction in Duchenne muscular dystrophy.

Although bladder function is thought to be unaffected in Duchenne muscular dystrophy, 46/88 boys interviewed had urinary problems. Nine underwent video urodynamics, showing in eight a small capacity, hyperreflexic bladder, and in the ninth (post spinal surgery) hyperreflexia and detrusor sphincter dyssynergia. Urinary dysfunction is a treatable feature of DMD.

Long mutant dystrophins and variable phenotypes: evasion of nonsense-mediated decay?

More than 98% of Duchenne muscular dystrophy (DMD) mutations result in the premature termination of the dystrophin open reading frame at various points over its 11-kb length. Despite this wide variation in coding potential (0%-98.6% of the full-length protein), the truncating mutations are associated with a surprisingly uniform severity of phenotype. This uniformity is probably attributable to ablation of the message by nonsense-mediated decay (NMD). The rare truncating mutations that occur near the 3' end of the dystrophin gene (beyond exon 70) can however result in extremely variable phenotypes (both intra- and inter-familially). We suggest that all proteins encoded by such mutant genes are capable in principle of rescuing the DMD phenotype but that NMD abrogates the opportunity to effect this rescue. The observed variability may therefore reflect an underlying variation in the efficiency of NMD between individuals. We discuss this hypothesis with particular reference to a well-characterised Becker muscular dystrophy patient with a frameshift mutation, where expression of a truncated dystrophin rescues the muscular but not mental phenotype.

Prenatal onset spinal muscular atrophy.

Five patients with severe spinal muscular atrophy (SMA) type I, all of whom presented with reduced fetal movements in utero, severe weakness at birth, and short survival time were assessed to attempt to determine whether their phenotype could be explained by their genotype. The diagnosis was confirmed by clinical, electrophysiological and histopathological features. Polymerase chain reaction assays were used to define the molecular diagnosis. A gene-dosage assay was used to assess the quantity of centromeric survival motor neuron gene (SMNc) present. In all cases the telomeric survival motor neuron gene (SMNt) was absent. The SMNc gene was present but in reduced copy number compared with a control group of children with less severe type I SMA, so may be important in determining severity. In the differential diagnosis of reduced fetal movements, SMA should be considered. The clinical classification may in future be clarified by molecular genetic findings.