Clinical and laboratory features of patients with myophosphorylase deficiency (McArdle disease).

Mutations of PYGM, the gene encoding human myophosphorylase, produce a metabolic myopathy characterised by exercise intolerance and, in some patients, myoglobinuria. To illustrate the clinical and laboratory features of myophosphorylase deficiency, we describe 10 patients diagnosed in Auckland, New Zealand, between 1989 and 2009. We review the clinical, biochemical, and histologic features and the results of mutation analysis. All patients reported exercise intolerance since childhood or the teenage years, starting within minutes of moderate or intense exertion. The "second wind" phenomenon, or myoglobinuria, were each reported in about half the patients. The serum creatine kinase concentration was elevated in all patients where this had been measured. Muscle biopsies revealed subsarcolemmal vacuolation and histochemical absence of myophosphorylase. Analysis of PYGM showed mutations in all alleles, most commonly Arg49Ter or Gly204Ser. One patient harbored a novel mutation, Pro488Arg, predicted to seriously disrupt the tertiary structure of the enzyme. Myophosphorylase deficiency produces a fairly uniform set of symptoms, and consistent elevation of the serum creatine kinase concentration. The diagnosis can be confirmed in most patients by mutation analysis using a blood sample.

Two-dimensional gel electrophoresis in inclusion body myositis.

Inclusion body myositis (IBM) is an acquired inflammatory myopathy in which a wide range of proteins is deposited within the cytoplasm of muscle fibres. To explore the possibility that this deposition occurs due to uncontrolled protein production arising from a defect at the nuclear level, we studied muscle samples from IBM and control subjects using two-dimensional gel electrophoresis. Twenty-seven gels from five controls and 24 gels from six patients with IBM were exhaustively compared using image analysis software and visual inspection. We found significant intra- and inter-subject variability in the number of protein spots on the gels. From 2272 to 4522 spots were found in different control gels, and from 2821 to 4153 spots in the IBM gels. No unique spots were identified in the IBM gels. When viewed with other work, the results of this study suggest that widespread, uncontrolled activation of genes is unlikely to be a component of the pathogenesis in IBM.

Bilateral brachial plexopathy following laparoscopic bariatric surgery.

This report describes a case of postoperative bilateral brachial plexopathy following laparoscopic bariatric surgery. The patient, a 39-year-old morbidly obese man, developed motor and sensory deficit, loss of reflexes, and pain in both arms postoperatively. Slow, but complete recovery occurred over nine months. We postulate that the head-up position in obese patients, without specific arm support, is a risk factor for brachial plexus injury.

Subacute measles encephalitis in an immunocompetent adult.

Subacute sclerosing panencephalitis (SSPE) and subacute measles encephalitis (SME) are both rare complications of measles virus infection. SSPE typically affects immunocompetent children, has an insidious onset and follows a steadily progressive course. SME mainly occurs in immunosuppressed children and has a rapidly progressive course. We describe a 43 year old immunocompetent man who presented with a rapidly progressive fatal encephalopathy. Histological examination of the brain showed a meningoencephalitis with inclusion bodies. Complement fixing antibody to measles virus was present in his serum and CSF. Measles virus RNA was found in the brain, spinal cord and eye, but not in the CSF. Analysis of the nucleoprotein gene isolated from this patient did not show similarity to SSPE strains of the measles virus. This patient demonstrates that subacute encephalitis secondary to measles virus infection can develop in an immunocompetent adult host.

Presentation of intravascular lymphomatosis as lumbosacral polyradiculopathy.

A 53-year-old man developed progressive sensory disturbance and weakness in the legs, sphincter disturbance, back pain, systemic symptoms, and pancytopenia. Electrophysiological tests indicated a widespread lumbosacral polyradiculopathy. Spinal magnetic resonance imaging and routine cerebrospinal fluid analysis showed minor nonspecific abnormalities. Bone marrow and liver biopsies showed hemophagocytosis; and polymerase chain reaction of cerebrospinal fluid, bone marrow, and serum suggested active infection with human herpesvirus-6. Autopsy revealed that his neurological symptoms resulted from intravascular lymphomatosis (angiotropic large cell lymphoma), a rare variant of lymphoma with predilection for the nervous system.

A novel ryanodine receptor mutation and genotype-phenotype correlation in a large malignant hyperthermia New Zealand Maori pedigree.

Malignant hyperthermia (MH) is a pharmacogenetic disorder that predisposes to a sometimes fatal hypermetabolic reaction to halogenated anaesthetics. MH is considered to originate from abnormal regulation of skeletal muscle Ca(2+) release. Current diagnosis of MH susceptibility (MHS) relies on in vitro contracture testing (IVCT) of skeletal muscle. The ryanodine receptor (RYR1) encoding the major Ca(2+) release channel in the skeletal muscle sarcoplasmic reticulum has been shown to be mutated in a number of MH pedigrees. The large Maori pedigree reported here is the largest MHS pedigree investigated to date and comprises five probands who experienced clinical episodes of MH and 130 members diagnosed by the IVCT. Sequencing of the 15 117 bp RYR1 cDNA in a MHS individual from this pedigree identified a novel C14477T transition that results in a Thr4826 to Ile substitution in the C-terminal region/transmembrane loop of the skeletal muscle ryanodine receptor. This is the first mutation in the RyR1 C-terminal region associated solely with MHS. Although linkage analysis showed strong linkage (max LOD, 11.103 at theta = 0.133) between the mutation and MHS in the pedigree using the standardized European IVCT phenotyping protocol, 22 MHS recombinants were observed. The relationship between the IVCT response and genotype was explored and showed that as IVCT diagnostic cut-off points were made increasingly stringent, the number of MHS discordants decreased with complete concordance between the presence or absence of the C14477T mutation and MHS and MH normal phenotypes, respectively, using a cut-off of 1.2 g tension at 2.0 mM caffeine and 1.8 g tension at 2.0% halothane. Many MHS pedigrees investigated have been excluded from linkage to the RYR1 gene on the basis of a small number of recombinants; however, the linkage analysis reported here suggests that other recombinant families excluded from linkage to the RYR1 gene may actually demonstrate linkage as the number of members tested within the pedigrees increases. The high number of discordants observed using the standardized diagnostic cut-off points is likely to reflect the presence of a second MHS susceptibility locus in the pedigree.

Inclusion body myositis: abnormal protein accumulation does not trigger apoptosis.

To examine whether apoptosis may contribute to muscle fiber loss in inclusion body myositis, we used the terminal deoxynucleotidyl transferase-mediated X-dUTP nick-end labeling (TUNEL) assay to compare the occurrence of DNA fragmentation in muscle samples from patients with inclusion body myositis and polymyositis. TUNEL-positive nuclei in nonnecrotic muscle fibers were rare even in the vicinity of amyloid-like material; significantly more frequent in polymyositis than inclusion body myositis; and several times less frequent than necrotic muscle fibers or mononuclear cell myocytotoxicity in both patient groups. Apoptosis is unlikely to play a significant role in the pathogenesis of inclusion body myositis.

Intestinal pseudo-obstruction, myasthenia gravis, and thymoma.

Two patients presented with abdominal pain, recurrent vomiting, weight loss, and constipation secondary to intestinal pseudo-obstruction. Both patients had symptoms and signs of myasthenia gravis, acetylcholine receptor antibodies, and thymoma. In one patient inflammatory cell infiltrates and occasional degenerate neurons were found in the myenteric plexus. The gastrointestinal symptoms resolved during treatment with pyridostigmine. The close temporal relationship between the onset of the gastrointestinal symptoms and the detection of myasthenia gravis and thymoma suggests that intestinal pseudo-obstruction can be a paraneoplastic syndrome associated with thymoma.

New mutations in acetylcholine receptor subunit genes reveal heterogeneity in the slow-channel congenital myasthenic syndrome.

Mutations in genes encoding the epsilon, delta, beta and alpha subunits of the end plate acetylcholine (ACh) receptor (AChR) are described and functionally characterized in three slow-channel congenital myasthenic syndrome patients. All three had prolonged end plate currents and AChR channel opening episodes and an end plate myopathy with loss of AChR from degenerating junctional folds. Genetic analysis revealed heterozygous mutations: epsilon L269F and delta Q267E in Patient 1, beta V266M in Patient 2, and alpha N217K in Patient 3 that were not detected in 100 normal controls. Patients 1 and 2 have no similarly affected relatives; in Patient 3, the mutation cosegregates with the disease in three generations. epsilon L269F, delta Q267E and beta V266M occur in the second and alpha N217K in the first transmembrane domain of AChR subunits; all have been postulated to contribute to the lining of the upper half of the channel lumen and all but delta Q267E are positioned toward the channel lumen, and introduce an enlarged side chain. Expression studies in HEK cells indicate that all of the mutations express normal amounts of AChR. epsilon L269F, beta V266M, and alpha N217K slow the rate of channel closure in the presence of ACh and increase apparent affinity for ACh; epsilon L269F and alpha N217K enhance desensitization, and epsilon L269F and beta V266M cause pathologic channel openings in the absence of ACh, rendering the channel leaky, delta Q267E has none of these effects and is therefore a rare polymorphism or a benign mutation. The end plate myopathy stems from cationic overloading of the postsynaptic region. The safety margin of neuromuscular transmission is compromised by AChR loss from the junctional folds and by a depolarization block owing to temporal summation of prolonged end plate potentials at physiologic rates of stimulation.

Congenital myasthenic syndrome caused by prolonged acetylcholine receptor channel openings due to a mutation in the M2 domain of the epsilon subunit.

In a congenital myasthenic syndrome with a severe endplate myopathy, patch-clamp studies revealed markedly prolonged acetylcholine receptor (AChR) channel openings. Molecular genetic analysis of AChR subunit genes demonstrated a heterozygous adenosine-to-cytosine transversion at nucleotide 790 in exon 8 of the epsilon-subunit gene, predicting substitution of proline for threonine at codon 264 and no other mutations in the entire coding sequences of genes encoding the alpha, beta, delta, and epsilon subunits. Genetically engineered mutant AChR expressed in a human embryonic kidney fibroblast cell line also exhibited markedly prolonged openings in the presence of agonist and even opened in its absence. The Thr-264-->Pro mutation in the epsilon subunit involves a highly conserved residue in the M2 domain lining the channel pore and is likely to disrupt the putative M2 alpha-helix. Our findings indicate that a single mutation at a critical site can greatly alter AChR channel kinetics, leading to a congenital myasthenic syndrome. This observation raises the possibility that mutations involving subunits of other ligand-gated channels may also exist and be the basis of various other neurologic or psychiatric disorders.

Patch-clamp analysis of the properties of acetylcholine receptor channels at the normal human endplate.

Normative data were obtained on the kinetic properties of the acetylcholine receptor (AChR) channel at the human motor endplate by patch-clamp analysis. Single channel currents were recorded from 34 endplates of 8 nonweak subjects in the presence of 1 micron acetylcholine (ACh) at 22 +/- 0.5 degrees C. The vast majority of channels opened to a conductance of about 60 pS. The dwell-time distributions of these channels were well described as the sum of two exponential functions. The mean duration of the dominant longer component was 1.9 ms for the open intervals and 3.04 ms for the bursts. At three endplates, a small proportion of the channels had lower conductance and longer open time, resembling immature AChR channels. At 28 endplates it was also possible to obtain an estimate of the rate constant for channel closure (alpha) and approximate estimates for the rate constants of channel opening (beta) and ACh dissociation (k-2). Estimates of k-2 varied by 15% with methods of estimation. This is attributed to errors inherent in estimating the duration of the briefest channel events. The normative data will be useful for evaluating pathologic alterations in the kinetic properties of the AChR channel found in some congenital myasthenic syndromes.

Congenital endplate acetylcholinesterase deficiency.

Endplate acetylcholinesterase (AChE) consists of globular catalytic subunits attached to the basal lamina by a collagen-like tail. Different genes encode the catalytic subunit and the tail portion of the enzyme. Endplate AChE deficiency was reported previously in a single case (Engel et al., 1977, patient 1). We describe here our observations in four additional patients (patients 2-5). Three cases were sporadic; patients 2 and 3 were sisters. All had generalized weakness increased by exertion but ophthalmoparesis was not a constant feature. All had mild slowing of the pupillary light reflex; other dysautonomic features were absent. None benefited from anticholinesterase therapy. All patients had a decremental electromyogram response; in four of the five patients, single nerve stimuli evoked a repetitive response. Miniature endplate potential amplitude was reduced in patient 5 only. Endplate amplitudes and currents were prolonged but the open-time of the acetylcholine receptor ion channel was normal. In patients 1-4 the quantal content of the endplate potential was reduced due to a reduced number of readily releasable quanta. Quantitative electron microscopy revealed abnormally small nerve terminals, abnormal encasement of the presynaptic membrane by Schwann cells and degeneration of junctional folds and of organelles in the junctional sarcoplasm. Acetylcholinesterase was absent from all endplates of all patients by cytochemical and immunocytochemical criteria. Density gradient ultracentrifugation of muscle extracts from patients 1, 3, 4 and 5 revealed an absence of the collagen-tailed form of the enzyme in patients 1, 3 and 4 but not in patient 5. The kinetic properties of the residual AChE in muscle were normal. Erythrocyte AChE activity and Km values, determined in three patients, were also normal. Studies of the catalytic subunit gene of AChE in patients 2 and 3 revealed no abnormality in those exons that encode the domain to which the tail subunit binds. In patients 1-4 the molecular defect is likely to reside in the gene encoding the tail subunit of AChE, or in a protein necessary to assemble the catalytic and tail subunits. In patient 5, the absence of AChE from the endplate may be due to a faulty tail subunit, a defect in the basal lamina site that binds the tail subunit or failure of transport of the assembled asymmetric enzyme from the cell interior to the basal lamina. The cause of the weakness in these patients is not fully understood but possible mechanisms are discussed.

A comparison between electroencephalography and somatosensory evoked potentials for outcome prediction following severe head injury.

The value of somatosensory evoked potentials (SEPs) for the prediction of outcome following severe head injury (HI) is established. The role of the electroencephalogram (EEG) in this setting is uncertain. In this comparative study, SEPs and EEGs were recorded within 3 days of severe HI in 90 patients, and the results related to outcome at 6 months. Patients with an isoelectric EEG or an EEG with repeated isoelectric intervals died. Reactivity of the EEG to external stimulation tended to be associated with favorable outcome. Grading of the EEGs on the basis of frequency composition otherwise provided no prognostic information. The presence of SEP scalp potentials bilaterally predicted favorable outcome, particularly if the central conduction times were normal. Conversely, the absence of one of both scalp potentials was associated with unfavorable outcome. EEGs thus provided useful prognostic information in only a minority of patients. By comparison, SEPs allowed prediction of both favorable and unfavorable outcomes in a much larger number of patients, and were therefore prognostically superior.

Cryptococcal meningitis in Auckland 1969-89.

Twenty-six patients with cryptococcal meningitis were seen in Auckland between 1969 and 1989. The incidence of cryptococcal meningitis in Auckland residents was 0.12 cases/100,000/year. Ten (38%) of the patients were Maori or Pacific Island Polynesians. Nineteen (73%) had a predisposing cause, including immunosuppressive therapy in nine and the acquired immunodeficiency syndrome (AIDS) in seven. The most common presenting syndrome was a subacute or chronic meningitis. Other clinical syndromes included a slowly progressive ataxia, polyradiculopathy, and headache with vomiting. In two patients, the symptoms of meningitis were overshadowed by those of systemic cryptococcal infection. Delay in making the diagnosis was common. The most sensitive method for diagnosing cryptococcal meningitis was the cerebrospinal fluid cryptococcal antigen test. Antifungal therapy cured 17 of the 25 (68%) treated patients overall, 15 of the 19 (79%) without AIDS and six of the seven with no underlying disease.

Pituitary apoplexy.

Pituitary apoplexy, a rare neurological emergency resulting from pituitary haemorrhage or infarction, should be considered a possibility in patients presenting with headache. Six cases are reported. The patients, four females and two males, ranged in age from 18 to 53 years. In only two had pituitary pathology previously been recognised. Headache occurred in all patients, visual field defects in four, ocular paresis in two, and subsequent hypopituitarism in five. The headache type suggested intracranial catastrophe in only one patient. A possible precipitant was noted for three of the episodes, including, in one patient, salmonella gastroenteritis. Cortisol deficiency during the acute event was common. Semi-urgent surgery was performed in two patients. In two others, prompt resolution of symptoms occurred following administration of dexamethasone.