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Defects of mitochondrial polymerase gamma (POLG) underlie neurological diseases ranging from myopathies to parkinsonism and infantile Alpers syndrome. The most severe manifestations have been associated with mutations of the 'spacer' region of POLG, the function of which has remained unstudied in humans. We identified a family, segregating three POLG amino acid variants, A467T, R627Q and Q1236H. The first two affect the spacer region and the third is a polymorphism, allelic with R627Q. Three grades of disease severity appeared to correlate with the genotypes. The patient with the most severe outcome, cerebellar ataxia syndrome, had all three variants, those with R627Q and Q1236H had juvenile-onset ptosis and gait disturbance and those with a single A467T allele had late-onset ptosis. To evaluate the molecular pathogenesis of these spacer defects, we expressed and purified the mutant proteins and studied their catalytic properties in vitro. The A467T substitution resulted in clearly decreased activity, DNA binding and processivity of the polymerase. Our biochemical data, the dominant manifestation of A467T and its previously reported high frequency in the Belgian population (0.6%), emphasize the role of this mutation as a common cause of neurological disease. Further, biochemical evidence that a polymorphic variant may modify the function of a mutant POLG, if occurring in the same polypeptide, is shown here. Finally, and surprisingly, other pathogenic spacer mutants showed DNA-binding affinities and processivities similar to or higher than the controls, suggesting that the disease-causing mechanisms of spacer mutations extend beyond the basic catalytic functions of POLG.

Creutzfeldt-Jakob disease (CJD) and Alzheimer's disease (AD) share clinical, neuropathological, and pathogenetic features. To investigate eventual mutual influences, we screened prominently affected neocortex from 110 neuropathologically proven CJD patients for Alzheimer-type pathology with anti-beta/A4, Bielschowsky and anti-tau (immuno)stains. The neuropathological classification of Alzheimer-type pathology was made according to the CERAD criteria. Results were controlled by comparison with Alzheimer-type changes in sections from the same cortical areas in 110 sex- and age-matched non-demented control patients. For comparison, the control patients were also classified according to the CERAD neuropathology criteria as if they had been demented. Alzheimer-type tissue changes as in definite and probable CERAD AD occur in 10.9% of the CJD patients and 19.1% of control patients (P=0.11). The median age of CJD and control patients with CERAD AD is 72 and 68 years, respectively, which differs significantly from the median ages of 64 and 63 years, respectively, in the non-AD/CJD and non-AD control patients. Since CERAD criteria include "presence of other neuropathological lesions likely to cause dementia", an AD diagnosis in CJD patients (all of whom are demented) is solely based on densities of neuritic plaques. Similar Alzheimer-type changes in even higher frequency, however, are also present in elderly non-demented controls. Thus, the coexistence of Alzheimer-type pathology in CJD most likely represents an age-related change. Deposits of prion protein (PrP) frequently accumulate at the periphery of beta/A4 plaques. The presence of beta/A4 amyloid in the brain may influence PrP morphogenesis.

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Amyotrophic lateral sclerosis (ALS) is characterized by progressive denervation leading to muscle atrophy prevented, during the early phase, by compensatory reinnervation. Little is known about muscle fibre regeneration capacity in ALS. We have carried out in vivo and in vitro investigation of skeletal muscle in ALS. Seven ALS patients underwent a deltoid muscle biopsy. Immunohistochemical analysis revealed various degrees of denervation- and reinnervation-related changes in the ALS muscle biopsies including satellite cells (SCs) activation and regenerating fibres. Only 3/7 primary cultures of ALS muscle cells were successfully established and had sufficient myogenicity, as assessed by desmin positivity, to be used without further purification. This was in contrast with the cultures derived from control muscles, predominantly desmin-positive cells. Although capable to proliferate in vitro, ALS-derived SCs presented an abnormal senescent-like morphology. Markers of senescence, including senescent-associated (SA)-βGal activity and p16 expression, were increased. Furthermore, ALS-derived SCs were also unable to fully differentiate in vitro as shown by abnormal myotubes morphology and reduced MHC isoform expression, compared to control myotubes. Our study suggests that SC function is altered in ALS. This could limit the efficacy of compensatory processes and therefore could contribute to the progression of muscle atrophy and weakness.

Objective Develop response criteria for juvenile dermatomyositis (JDM). Methods We analyzed the performance of 312 definitions that used core set measures (CSM) from either the International Myositis Assessment and Clinical Studies Group (IMACS) or the Pediatric Rheumatology International Trials Organization (PRINTO) and were derived from natural history data and a conjoint-analysis survey. They were further validated in the PRINTO trial of prednisone alone compared to prednisone with methotrexate or cyclosporine and the Rituximab in Myositis trial. Experts considered 14 top-performing candidate criteria based on their performance characteristics and clinical face validity using nominal group technique at a consensus conference. Results Consensus was reached for a conjoint analysis–based continuous model with a Total Improvement Score of 0-100, using absolute percent change in CSM with thresholds for minimal (≥30 points), moderate (≥45), and major improvement (≥70). The same criteria were chosen for adult dermatomyositis/polymyositis with differing thresholds for improvement. The sensitivity and specificity were 89% and 91-98% for minimal, 92-94% and 94-99% for moderate, and 91-98% and 85-85% for major improvement, respectively, in JDM patient cohorts using the IMACS and PRINTO CSM. These criteria were validated in the PRINTO trial for differentiating between treatment arms for minimal and moderate improvement (P=0.009–0.057) and in the Rituximab trial for significantly differentiating the physician rating of improvement (P<0.006). Conclusion The response criteria for JDM was a conjoint analysis–based model using a continuous improvement score based on absolute percent change in CSM, with thresholds for minimal, moderate, and major improvement.

ObjectiveSporadic inclusion body myositis (sIBM), the most frequent myositis in elderly patients, is characterized by the presence muscle inflammation and degeneration. We aimed at characterizing immune responses and regulatory T cells, considered key players in the maintenance of peripheral immune tolerance, in sIBM.MethodsSerum and muscle tissue levels of 25 cytokines and phenotype of circulating immune cells were measured in 22 sIBM patients and compared with 22 healthy subjects. Cytokine data were analysed by unsupervised hierarchical clustering and principal components analysis.ResultsCompared to healthy controls, sIBM patients had increased levels of Th-1 cytokines and chemokines such as IL-12 (261±138 pg/mL vs. 88±19 pg/mL; p<0.0001), CXCL-9 (186±12 pg/mL vs. 13±7 pg/mL; p<0.0001), and CXCL-10 (187±62 pg/mL vs. 13±6 pg/mL; p<0.0001). This was associated with an increased frequency of CD8+CD28− T cells (45.6±18.5% vs. 13.5±9.9%; p<0.0001), which were more prone to produce IFN-γ (45.6±18.5% vs. 13.5±9.9%; p<0.0001). sIBM patients also had a decreased frequency of circulating regulatory T cells (CD4+CD25+CD127lowFOXP3+, 6.9±1.7%; vs. 5.2±1.1%, p = 0.01), which displayed normal suppressor function and were also present in affected muscle.ConclusionsIBM patients present systemic immune activation with Th1 polarization involving the IFN-γ pathway and CD8+CD28− T cells associated with peripheral regulatory T cell deficiency.