Search

Being a doctor in the 21st Century requires a diverse range of skills, a broad base of knowledge and a suite of professional values and attitudes that enable the clinical practice to be safe, effective and caring. Doctors, irrespective of their speciality, need to be knowledgeable and skilful not just in their area of expertise but also need a range of generic skills and capabilities such as communication, leadership, academic scholarship and research, teaching, quality improvement, advocacy, digital literacy to name a few. These capabilities, all relevant to clinical practice, are assessed routinely in clinical settings. This rich information about trainees, available from their formative assessments, does not inform high-stakes judgements about progression. Instead, these judgements are usually made on the basis of summative examinations conducted in simulated settings. Unfortunately, these summative assessments have consistently delivered results with a large magnitude of the differential between the outcomes of candidates, based on factors such as ethnicity, gender, other protected characteristics and also the country of primary medical qualification. Formative assessment during training, however, is individualised and tends not to show this level of difference; leading to a situation where failure in summative examinations comes as a surprise to both trainees and to training programme directors. There is evidence that periodic assessment of trainees’ acquisition of core capabilities can help make balanced, informed judgements about readiness for progression. The move from a pass/fail categorisation to a yet/not yet categorisation when coupled with appropriate remedial measures can improve, both the validity, as well as the fairness of assessments. The large magnitude of the differential in outcomes of high-stakes assessments cannot be fixed by tweaking current assessment systems. Instead, there needs to be a recognition that high-level of capabilities consistently demonstrated in the workplace need to play a role in judgements about progression. Failure to do so is unfair, wasteful of public finances, and in breach of the trust places by the public, in training safe and competent clinicians.

“There is a culture change required at the grass-root level for this project to succeed and clinical engagement is paramount.”

Extraocular muscle (EOM) is spared in Duchenne muscular dystrophy. Here, we tested putative EOM sparing mechanisms predicted from existing dystrophinopathy models. Data show that mdx mouse EOM contains dystrophin-glycoprotein complex (DGC)-competent and DGC-deficient myofibers distributed in a fiber type-specific pattern. Up-regulation of a dystrophin homologue, utrophin, mediates selective DGC retention. Counter to the DGC mechanical hypothesis, an intact DGC is not a precondition for EOM sarcolemmal integrity, and active adaptation at the level of calcium homeostasis is not mechanistic in protection. A partial, fiber type-specific retention of antiischemic nitric oxide to vascular smooth muscle signaling is not a factor in EOM sparing, because mice deficient in dystrophin and alpha-syntrophin, which localizes neuronal nitric oxide synthase to the sarcolemma, have normal EOMs. Moreover, an alternative transmembrane protein, alpha7beta1 integrin, does not appear to substitute for the DGC in EOM. Finally, genomewide expression profiling showed that EOM does not actively adapt to dystrophinopathy but identified candidate genes for the constitutive protection of mdx EOM. Taken together, data emphasize the conditional nature of dystrophinopathy and the potential importance of nonmechanical DGC roles and support the hypothesis that broad, constitutive structural cell signaling, and/or biochemical differences between EOM and other skeletal muscles are determinants of differential disease responsiveness.

This review summarizes an alternative approach to the understanding of neuromuscular disease. By contrasting disease susceptibility of extraocular muscle and ocular motor neurons, it is hoped that unique insights into disease mechanisms may be identified. Disorder of eye movements leads to dramatic symptoms for patients and the ocular motor system is relatively limited in its ability to compensate rapidly for such disruptions. However, more profound reasons exist as to why myasthenia gravis compromises neuromuscular transmission at ocular muscle synapses as well as why Graves' ophthalmopathy exists. In contrast, muscular dystrophies spare the eye muscles while devastating all other skeletal muscles; the same is true for motor neuron diseases. It is hoped that this review will encourage others to view the world of neuromuscular diseases as delineated into those that spare the ocular motor system and those that do not.

Mutations in dystrophin cause Duchenne muscular dystrophy (DMD), but absent dystrophin does not invariably cause necrosis in all muscles, life stages and species. Using DNA microarray, we established a molecular signature of dystrophinopathy in the mdx mouse, with evidence that secondary mechanisms are key contributors to pathogenesis. We used variability controls, adequate replicates and stringent analytic tools, including significance analysis of microarrays to estimate and manage false positive rates. In leg muscle, we identified 242 differentially expressed genes, >75% of which have not been previously reported as altered in human or animal dystrophies. Data provide evidence for coordinated activity of numerous components of a chronic inflammatory response, including cytokine and chemokine signaling, leukocyte adhesion and diapedesis, invasive cell type-specific markers, and complement system activation. Selective chemokine upregulation was confirmed by RT-PCR and immunoblot, and may be a key determinant of the nature of the inflammatory response in dystrophic muscle. Up-regulation of secreted phosphoprotein 1 (minopontin, osteopontin) mRNA and protein in dystrophic muscle identified a novel linkage between inflammatory cells and repair processes. Extracellular matrix genes were up-regulated in mdx to levels similar to those in DMD. Since, unlike DMD, mdx exhibits little fibrosis, data suggest that collagen regulation at post-transcriptional stages mediates extensive fibrosis in DMD. Taken together, these data identify a relatively neglected aspect of DMD, suggest new treatment avenues, and highlight the value of genome-wide profiling in study of complex disease processes.

Extraocular muscles (EOMs) are specialized skeletal muscles that are constantly active, generate low levels of force for cross sectional area, have rapid contractile speeds, and are highly fatigue resistant. The neuronal isoform of nitric oxide synthase (nNOS) is concentrated at the sarcolemma of fast-twitch muscles fibers, and nitric oxide (NO) modulates contractility. This study evaluated nNOS expression in EOM and the effect of NO modulation on lateral rectus muscle's contractility. nNOS activity was highest in EOM compared with diaphragm, extensor digitorum longus, and soleus. Neuronal NOS was concentrated to the sarcolemma of orbital and global singly innervated fibers, but not evident in the multi-innervated fibers. The NG-nitro-L-arginine methyl ester (L-NAME, a NOS inhibitor), increased submaximal tetanic and peak twitch forces. The NO donors S-nitroso-N-acetylcysteine (SNAC) and spermineNONOate reduced submaximal tetanic and peak twitch forces. The effect of NO on the contractile force of lateral rectus muscle is greater than previously observed on other skeletal muscle. NO appears more important in modulating contraction of EOM compared with other skeletal muscles, which could be important for the EOM's specialized role in generation of eye movements.

5-Hydroxytryptamine (serotonin, 5-HT) affects upper airway and chest wall inspiratory muscle control. The purpose of this study was to investigate the relative interaction of serotonergic agents on these two muscle groups. We measured the responses of the hypoglossal and phrenic nerves to the systemic administration of serotonergic-active agents and determined the receptor types through which these agents act in anesthetized, vagotomized, paralyzed and artificially ventilated rats. The serotonin precursor, L-5-hydroxytryptophan (L-5-HTP) produced equivalent stimulation of phasic inspiratory activity of the hypoglossal and phrenic nerves. General serotonin antagonists produced significant and equivalent diminution of both motoneuron pools. Specific 5-HT1A stimulation and 5-HT1C/2 antagonism enhanced ventilatory activity. We conclude: (1) a baseline level of serotonergic input to hypoglossal and phrenic motoneuron pools was present, (2) different 5-HT receptors had different effects on ventilatory neural activity, and (3) hypoglossal and phrenic motoneuron pools responded similarly to the serotonergic agents given.

Myasthenia gravis (MG) is a neuromuscular transmission disease caused primarily by acetylcholine receptor (AChR) autoantibodies,1,2 and several lines of evidence indicate that the fixation of complement at the neuromuscular junction (NMJ) is an important factor in determining disease severity.3 C3 activation fragments and the membrane attack complex are detected at the NMJ of patients with MG, depletion of serum C3 and C4 is appreciated in some patients, and terminal complement components are found in patient sera.4 – 6 In humans, antigenic modulation and direct blockade of the AChR also likely contribute to MG pathology, but their relative significance is not known.7,8 Complement is paramount in driving disease pathology in both models of the experimentally acquired myasthenia gravis (EAMG), whether produced by administration of AChR antibodies or through immunization with purified AChR. With rare exception,9 passive transfer EAMG is induced only by complement-fixing antibodies, and complement depletion by cobra venom factor eliminates NMJ injury and weakness.10 Antibodies directed toward C511 and soluble complement receptor (sCR1)12 are protective in EAMG produced by AChR antibody administration. C5-deficient mice13 or anti-C6 Fab antibody–treated EAMG rats14 are more resistant and develop less severe disease, whereas an absence of cell surface regulators of complement leads to significantly greater disease with EAMG induced by AChR antibodies.15–17 The inhibition of complement as a therapeutic approach is beginning to be applied to human disorders. Pexelizumab, a monoclonal antibody directed against C5, has demonstrated short-term safety and efficacy in humans in myocardial infarction,18 coronary artery bypass graft surgery,19 and lung transplantation.20 A phase 3 trial of eculizumab, a single-chain fragment of anti-C5, in treatment of paroxysmal nocturnal hemoglobinuria21 demonstrated significant clinical benefits with minimal adverse effects. MG would be expected to respond well to complement inhibition especially in acute exacerbations when complement-mediated NMJ injury is expected to be maximal. rEV576 is a novel complement inhibitor, which appears ideally suited for consideration as a therapeutic agent. It is a 17kDa protein22 identified from the saliva of the tick Ornithodoros moubata and belongs to the lipocalin family of proteins, which inhibit inflammatory mediators.23 Because the agent is derived from ticks that apply themselves to mammalian species for weeks without inducing a reaction, there is an expectation that rEV576 will have limited adverse effects in humans. The compound is not known to cause allergic reactions or to have effects beyond those related to complement inactivation.24 rEV576 specifically targets the C5 activation step and has been shown to inhibit both the classic and the alternative pathways, and act specifically at the C5 step of complement activation.25 The simplest explanation for the activity of rEV576 is direct binding to C5 that prevents interaction with the C5 convertase rather than by blocking the C5a cleavage site.26 In this study, the active and passive models of EAMG were used to investigate the therapeutic activity of rEV576. Rats treated with rEV576 demonstrated dramatic improvements in weakness, recovery from weight loss, and reduced C9 deposition at the NMJ. The findings suggest that this novel complement inhibitor could prove to be an effective treatment in human MG.

In myasthenia gravis (MG), neuromuscular transmission is disrupted due to the production of autoantibodies against acetylcholine receptors (AChR). In previous work, we showed that decay accelerating factor (DAF or CD55), an intrinsic cell surface complement regulator that disables C3/C5 amplification convertases, protects against receptor loss and muscle weakness. In this study, we examined whether, and if so, to what extent CD59, a downstream intrinsic cell surface regulator that prevents assembly of membrane attack complexes (MACs), contributes to this protection. Twenty-four hours after anti-AChR injection, we found that CD59a −/− mice did not significantly differ from WTs, all Daf1 −/− CD59a −/− mice either died or required euthanasia. At 48 h, Daf1 −/− were significantly weaker than CD59a −/− and WT mice, and for these mice immunohistochemistry revealed marked C9 deposition at postsynaptic junctions, radioimmunoassays showed reductions in AChR levels, and electron microscopy demonstrated massive junctional damage. These data indicate that DAF serves as the initial shield that protects the neuromuscular junction whereas CD59 is a further barrier. They argue that complement inhibitor, particularly if targeted to the receptor, could then have therapeutic value in human MG.

Complement activation at motor endplates is the primary effector mechanism in myasthenia gravis (MG). In this study, we evaluated whether differences in gene transcript levels and protein expression of cell-surface complement regulators could be a factor in the increased susceptibility of extraocular muscle (EOM) compared to other skeletal muscles to MG. Experimental autoimmune MG (EAMG) was induced in mice by administration of a monoclonal antibody (mAb) directed toward the acetylcholine receptor (AChR). Standard RT-PCR and real-time PCR (qPCR) were used to assess mRNA levels of decay-accelerating factor (DAF), CD59, and complement receptor 1-related gene/protein y (Crry). Gene transcript levels of the alpha- and gamma-subunits of the AChR were also evaluated by qPCR. Protein expression of the three intrinsic complement regulators at the neuromuscular junction was assessed by immunohistochemistry. Under constitutive conditions by RT-PCR, no significant differences were detected, but qPCR, EOM showed lower mRNA levels of all three complement regulators, but higher levels of alpha- and gamma-subunit gene transcripts. With EAMG, significant decreases in mRNA levels of all three complement regulators as well as AChR subunits occurred in EOM, but not in the diaphragm. Immunoreactivity for all three complement regulators was highly concentrated at diaphragm junctions, whereas it was less intense or absent at EOM junctions. With EAMG, immunoreactivity for Crry and DAF increased at diaphragm junctions and for DAF at EOM junctions. Diminished intrinsic complement regulatory activity may contribute to the susceptibility of EOM to MG. Our findings suggest that complement inhibitor-based therapies could be useful in treating ocular manifestations of MG.

The orbital tissues may form a unique immunological environment, as evidenced by autoimmune disorders that specifically target orbital tissues, particularly myasthenia gravis (MG) and Graves' ophthalmopathy (GO). The reasons for the preferential susceptibility are likely to be multiple, based on the interplay of molecular and physiological properties of extraocular muscles (EOM), the unique requirements of the ocular motor system, and the specific autoimmune pathology. Of general importance, even a minor loss of EOM force generation will sufficiently misalign the visual axes to produce dramatic symptoms, and proprioceptive feedback is limited to overcome such a deficit. Particular to MG, EOM synapses appear susceptible to neuromuscular blockade, the autoimmune pathology differs between ocular and generalized MG patients, and the influence of complement regulatory factors may be less prominent in preventing damage at EOM neuromuscular junctions. GO pathogenesis is poorly understood, but shared epitopes of orbital fibroblasts, EOM, and thyroid could lead to specific autoimmune targeting of these tissues. The differential response of orbital fibroblasts to cytokines may be a key factor in disease development. Greater appreciation of the immunologic environment of orbital tissues may lead to therapies specifically designed for orbital autoimmune diseases.