Jeffrey T. Guptill

Density and Distribution of Hippocampal Neurotransmitter Receptors in Autism: An Autoradiographic Study*

Neuropathological studies in autistic brains have shown small neuronal size and increased cell packing density in a variety of limbic system structures including the hippocampus, a change consistent with curtailment of normal development. Based on these observations in the hippocampus, a series of quantitative receptor autoradiographic studies were undertaken to determine the density and distribution of eight types of neurotransmitter receptors from four neurotransmitter systems (GABAergic, serotoninergic [5-HT], cholinergic, and glutamatergic). Data from these single concentration ligand binding studies indicate that the GABAergic receptor system (3[H]-flunitrazepam labeled benzodiazepine binding sites and 3[H]-muscimol labeled GABAA receptors) is significantly reduced in high binding regions, marking for the first time an abnormality in the GABA system in autism. In contrast, the density and distribution of the other six receptors studied (3[H]-8OH-DPAT labeled 5-HT1A receptors, 3[H]-ketanserin labeled 5-HT2 receptors, 3[H]-pirenzepine labled M1 receptors, 3[H]-hemicholinium labeled high affinity choline uptake sites, 3[H]-MK801 labeled NMDA receptors, and 3[H]-kainate labeled kainate receptors) in the hippocampus did not demonstrate any statistically significant differences in binding.

ANTI-MuSK ANTIBODY MYASTHENIA GRAVIS: CLINICAL FINDINGS AND RESPONSE TO TREATMENT IN TWO LARGE COHORTS

Introduction: Myasthenia gravis (MG) patients with autoantibodies to muscle‐specific tyrosine kinase (MuSK) represent a distinct subset of those with this disease. Treatment and outcomes data in these patients are limited and conflicting. Methods: We reviewed 110 MuSK‐MG patients from two large clinics in Italy and the USA. Results: Thirty‐nine to 49% of patients with generalized, acetylcholine receptor antibody (AChR‐Ab)–negative MG had MuSK‐MG. Eighty‐five percent were female, with disease onset typically in the fourth decade. Ocular and/or bulbar symptoms were present at onset in 79% of those studied. Eighty‐five percent were MGFA class III or greater, and crisis occurred in 28%. Plasma exchange (PLEX) produced improvement in 93%, whereas only 61% improved after intravenous immunoglobulin. Long‐term outcomes were comparable to those of patients with AChR‐Ab–positive MG. Conclusions: MuSK‐MG has a marked female predominance with frequent oculobulbar weakness and crises. Many patients deteriorate rapidly early in the disease, and PLEX is usually the preferred treatment. Long‐term outcomes are similar to those of patients with AChR‐Ab+ MG. Muscle Nerve 44: 36–40, 2011

Update on muscle-specific tyrosine kinase antibody positive myasthenia gravis.

PURPOSE OF REVIEW Important concepts regarding the pathogenesis, clinical features, diagnosis and treatment of muscle-specific tyrosine kinase (MuSK) antibody positive myasthenia gravis will be reviewed. Special attention will be paid to clinical phenotypes and treatment, particularly encouraging responses that have been reported to rituximab. RECENT FINDINGS Worldwide studies confirm three major phenotypes in MuSK antibody positive myasthenia gravis (MMG) patients: indistinguishable from acetylcholine receptor antibody positive patients, prominent faciopharyngeal weakness, usually with marked muscle atrophy, and relatively isolated neck extensor and respiratory weakness. MMG predominates in women and weakness is typically more severe, with more frequent respiratory crises than non-MuSK myasthenia gravis. Patients with sub-acute bulbar, shoulder, and neck weakness pose unique challenges in terms of differential diagnosis and electrodiagnosis. Electrodiagnostic studies evaluating for disorders of neuromuscular transmission should focus on proximal limb and facial muscles, as well as clinically weak muscles. The response to acetylcholinesterase inhibitors is often disappointing. Long-term outcomes appear favorable though patients typically require more aggressive immunosuppression. Uncontrolled observations report encouraging results with rituximab in the treatment of refractory MMG. The role of thymectomy in the management of these patients remains uncertain. SUMMARY MuSK antibody positive patients represent a unique subset of myasthenia gravis. Identification of these patients has important diagnostic and disease management implications.

Characterization of CD4 and CD8 T cell responses in MuSK myasthenia gravis.

Muscle specific tyrosine kinase myasthenia gravis (MuSK MG) is a form of autoimmune MG that predominantly affects women and has unique clinical features, including prominent bulbar weakness, muscle atrophy, and excellent response to therapeutic plasma exchange. Patients with MuSK MG have predominantly IgG4 autoantibodies directed against MuSK on the postsynaptic muscle membrane. Lymphocyte functionality has not been reported in this condition. The goal of this study was to characterize T cell responses in patients with MuSK MG. Intracellular production of IFN-gamma, TNF-alpha, IL-2, IL-17, and IL-21 by CD4+ and CD8+ T cells was measured by polychromatic flow cytometry in peripheral blood samples from 11 Musk MG patients and 10 healthy controls. Only one MuSK MG patient was not receiving immunosuppressive therapy. Regulatory T cells (Treg) were also included in our analysis to determine if changes in T cell function were due to altered Treg frequencies. CD8+ T cells from MuSK MG patients had higher frequencies of polyfunctional responses than controls, and CD4+ T cells had higher IL-2, TNF-alpha, and IL-17. MuSK MG patients had a higher percentage of CD4+ T cells producing combinations of IFN-gamma/IL-2/TNF-gamma, TNF-alpha/IL-2, and IFN-gamma/TNF-alpha. Interestingly, Treg numbers and CD39 expression were not different from control values. MuSK MG patients had increased frequencies of Th1 and Th17 cytokines and were primed for polyfunctional proinflammatory responses that cannot be explained by a defect in CD39 expression or Treg number.

Characterization of B cells in muscle-specific kinase antibody myasthenia gravis.

Objective: To characterize B-cell subsets in patients with muscle-specific tyrosine kinase (MuSK) myasthenia gravis (MG). Methods: In accordance with Human Immunology Project Consortium guidelines, we performed polychromatic flow cytometry and ELISA assays in peripheral blood samples from 18 patients with MuSK MG and 9 healthy controls. To complement a B-cell phenotype assay that evaluated maturational subsets, we measured B10 cell percentages, plasma B cell–activating factor (BAFF) levels, and MuSK antibody titers. Immunologic variables were compared with healthy controls and clinical outcome measures. Results: As expected, patients treated with rituximab had high percentages of transitional B cells and plasmablasts and thus were excluded from subsequent analysis. The remaining patients with MuSK MG and controls had similar percentages of total B cells and naïve, memory, isotype-switched, plasmablast, and transitional B-cell subsets. However, patients with MuSK MG had higher BAFF levels and lower percentages of B10 cells. In addition, we observed an increase in MuSK antibody levels with more severe disease. Conclusions: We found prominent B-cell pathology in the distinct form of MG with MuSK autoantibodies. Increased BAFF levels have been described in other autoimmune diseases, including acetylcholine receptor antibody–positive MG. This finding suggests a role for BAFF in the survival of B cells in MuSK MG, which has important therapeutic implications. B10 cells, a recently described rare regulatory B-cell subset that potently blocks Th1 and Th17 responses, were reduced, which suggests a potential mechanism for the breakdown in immune tolerance in patients with MuSK MG.

Stroke After Primary Percutaneous Coronary Intervention in Patients With ST-Segment Elevation Myocardial Infarction Timing, Characteristics, and Clinical Outcomes

Background—Stroke is a rare but potentially devastating complication of acute myocardial infarction. Little is known about stroke timing, characteristics, and clinical outcomes in patients with ST-segment elevation myocardial infarction treated with primary percutaneous coronary intervention (PCI). Methods and Results—We studied 5372 patients enrolled in the Assessment of Pexelizumab in Acute Myocardial Infarction (APEX-AMI) trial. We analyzed stroke incidence, type, timing, and association with the prespecified 90-day clinical outcomes. Cox proportional hazards modeling was performed to assess the relationship between stroke and outcomes, after adjusting baseline characteristics and analyzing stroke as a time-dependent covariate. Stroke occurred in 69 primary patients with PCI (1.3%). A third of strokes were ischemic (n=23; 33%), 12% (n=8) were hemorrhagic, and the remaining 55% (n=38) were of uncertain type. The median (25th, 75th percentile) time of stroke occurrence was 6 (3, 14) days. Overall, 43% of strokes occurred within 48 hours of PCI, and all hemorrhagic strokes occurred within 48 hours. Stroke was associated with an increased risk of 90-day death (unadjusted hazard ratio [HR], 8.0; 95% confidence interval [CI], 4.8–13.5), congestive heart failure (unadjusted HR, 3.2; 95% CI, 1.3–7.8), and 30-day hospital readmission (unadjusted HR, 3.2; 95% CI, 2.0–5.1). After adjustment, stroke was still strongly associated with 90-day death (adjusted HR, 5.6; 95% CI, 3.2–9.8) and the combination end point of death, congestive heart failure, or cardiogenic shock at 90 days (adjusted HR, 2.4; 95% CI, 1.2–4.7). Conclusions—Stroke is an infrequent complication in the setting of ST-segment elevation myocardial infarction treated with primary PCI but is associated with increased morbidity and mortality. Studies to determine mechanisms that may be responsible for strokes that occur >48 hours from primary PCI are warranted. Clinical Trial Registration—URL: http://www.clinicaltrials.gov. Unique identifier: NCT00091637.

Prolonged B cell depletion in MuSK myasthenia gravis following rituximab treatment

Rituximab (RTX) therapy is used increasingly to manage myasthenia gravis patients, and case series suggest particular benefit for those patients who have antibodies to muscle specific kinase (MuSK-MG).1 We report a MuSK-MG patient with persistent and severe B cell depletion 3 years after receiving RTX. A 62 year old woman developed ptosis, bulbar symptoms, and weight loss in 2000. In 2005 she developed hypercarbic respiratory failure and was eventually diagnosed with MuSK-MG. She had 3 additional hospitalizations for exacerbations, including one for crisis, and required BiPAP at night. An initial excellent response to therapeutic plasma exchange waned over time. Intravenous immunoglobulin, azathioprine, and prednisone did not provide significant improvement. In 2010, she was treated with 6 doses of 1000mg RTX over approximately 8 weeks (578 mg/m2 per infusion) and remained on prednisone and azathioprine. Following the RTX infusions she had a tenuous course and later developed progressive respiratory insufficiency and required nocturnal BiPAP. A chest CT showed no evidence of thymoma. Blood biomarker samples were drawn 34 months after RTX treatment, at which time she required supplemental oxygen. Clinical evaluation demonstrated persistent oculobulbar and facial weakness and disability (MG-composite: 23, MG-Manual Muscle Testing: 23, MG-Quality of Life-15: 30).2–5 We measured B cells by flow cytometry after staining for CD19 and identified helper and cytotoxic T cells by CD4 and CD8 expression, respectively. Polychromatic flow cytometry demonstrated 49.5% T helper and 44.7% cytotoxic T cells. Only 0.06% of lymphocytes were CD19+ B cells; naive, memory, and plasma cell subpopulations were undetectable (Figure). Repeat B cell markers performed over 36 months after her initial RTX treatment continued to show profound B cell depletion with <1% CD19+ B cells. Creatine kinase and thyroid profile were normal. She had had no serious infections. Figure Prolonged B cell depletion 34 months after rituximab treatment. Peripheral blood mononuclear cells from a healthy control, a patient with MuSK-MG, and our patient with MuSK-MG treated with rituximab were surface stained with CD19 PcP Cy5.5 conjugate. ... Following depletion with RTX, B cell populations typically recover within 12 months.6 This MuSK-MG patient had profound, prolonged B cell depletion 3 years after receiving RTX. It has been observed that recovery of B cell populations begins with naive B cells, and memory B cell regeneration may be delayed.7 However, in patients with autoimmune disease, such prolonged B cell depletion after RTX has only been reported in 2 systemic lupus erythematosus patients, both of whom were given RTX in combination with cyclophosphamide.8 In these cases, B cells remained low 5–7 years after RTX therapy. The underlying mechanism and the effect of concomitant cyclophosphamide therapy on the risk of developing prolonged B cell depletion with RTX are uncertain. In our case, it is also unclear how the unconventional RTX dosing regimen, combined with other immunosuppressive drugs, may have affected B cell recovery. Due to poor disease control, our patient continued to receive azathioprine and varying doses of prednisone, raising the risk for serious infections.9 As the use of RTX for neurologic diseases increases, clinicians need to be aware of the possibility of prolonged B cell depletion, particularly when it is combined with other immunosuppressives.

Current Treatment, Emerging Translational Therapies, and New Therapeutic Targets for Autoimmune Myasthenia Gravis

Myasthenia gravis (MG) is an autoimmune disease associated with the production of autoantibodies against 1) the skeletal muscle acetylcholine receptor; 2) muscle-specific kinase, a receptor tyrosine kinase critical for the maintenance of neuromuscular synapses; 3) low-density lipoprotein receptor-related protein 4, an important molecular binding partner for muscle-specific kinase; and 4) other muscle endplate proteins. In addition to the profile of autoantibodies, MG may be classified according the location of the affected muscles (ocular vs generalized), the age of symptom onset, and the nature of thymic pathology. Immunopathologic events leading to the production of autoantibodies differ in the various disease subtypes. Advances in our knowledge of the immunopathogenesis of the subtypes of MG will allow for directed utilization of the ever-growing repertoire of therapeutic agents that target distinct nodes in the immune pathway relevant to the initiation and maintenance of autoimmune disease. In this review, we examine the pathogenesis of MG subtypes, current treatment options, and emerging new treatments and therapeutic targets.

Myasthenia gravis and Lambert-Eaton myasthenic syndrome.

Purpose of Review: This article reviews the clinical presentations, diagnostic findings, and treatment options for autoimmune myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome. Recent Findings: Immunologic research is unraveling the immunopathology of MG and identifying targets for novel immune-based therapy of this condition. MG patients with antibodies to muscle-specific tyrosine kinase (MuSK) frequently present with symptoms and clinical findings that suggest nerve or muscle disease. Summary: Early diagnosis and treatment have a marked effect on outcome in these diseases. In most cases, the diagnosis of MG or Lambert-Eaton myasthenic syndrome can be made from the history, supplemented with directed questions, and a physical examination designed to demonstrate variable weakness in affected muscle groups. Appropriate confirmatory tests almost always establish the diagnosis. Although several novel treatment modalities for MG are under investigation, currently available therapies produce substantial improvement in function and quality of life in most patients with this condition. Knowledge about the dosing, adverse effects, and costs of immunomodulatory therapies is essential for the effective management of patients with MG and Lambert-Eaton myasthenic syndrome.

Cost analysis of myasthenia gravis from a large U.S. insurance database

Little is known about the costs of managing rare diseases, and comprehensive healthcare costs have not been reported for myasthenia gravis (MG). We evaluated the direct costs and healthcare resource utilization in insured MG patients.