SMDT1 variants impair EMRE-mediated mitochondrial calcium uptake in patients with muscle involvement

Ionic calcium (Ca2+) is a key messenger in signal transduction and its mitochondrial uptake plays an important role in cell physiology. This uptake is mediated by the mitochondrial Ca2+ uniporter (MCU), which is regulated by EMRE (essential MCU regulator) encoded by the SMDT1 (single-pass membrane protein with aspartate rich tail 1) gene. This work presents the genetic, clinical and cellular characterization of two patients harbouring SMDT1 variants and presenting with muscle problems. Analysis of patient fibroblasts and complementation experiments demonstrated that these variants lead to absence of EMRE protein, induce MCU subcomplex formation and impair mitochondrial Ca2+ uptake. However, the activity of oxidative phosphorylation enzymes, mitochondrial morphology and membrane potential, as well as routine/ATP-linked respiration were not affected. We hypothesize that the muscle-related symptoms in the SMDT1 patients result from aberrant mitochondrial Ca2+ uptake.

Pathogenic variants in three families with distal muscle involvement

Three families suspected of distal hereditary motor neuropathy underwent genetic screening with the aim to identify the molecular defect underlying the disease. The description of the identification reflects the shift in molecular diagnostics that was made during the last decades. Our candidate gene approach yielded a known pathogenic variant in BSCL2 (p.Asn88Ser) in one family, and via a CMT-capture, in HSPB1 (p.Arg127Trp), in addition to five other variations in Charcot-Marie-Tooth-related genes in the proband of the second family. In the third family, using whole exome sequencing, followed by linkage-by-location, a three base pair deletion in exon 33 of MYH7 (p.Glu1508del) was found, a reported pathogenic allele albeit for a myopathy. After identification of the causative molecular defect, cardiac examination was performed for patients of the third family and this demonstrated abnormalities in three out of five affected family members. Heterogeneity and expansion of clinical phenotypes beyond known characteristics requires a wider set of genes to be screened. Whole exome/genome analysis with limited prior clinical information may therefore be used to precede a detailed clinical evaluation in cases of large families, preventing screening of a too narrow set of genes, and enabling the identification of novel disease-associated genes. In our cases, the variants had been reported, and co-segregation analysis confirmed the molecular diagnosis.

Rhabdomyolysis after COVID-19 Comirnaty Vaccination: A Case Report

Rhabdomyolysis is an acute disruption in skeletal muscle integrity, leading to the rapid release of 4 muscle contents into the bloodstream, such as creatine kinase (CK). It can have various causes, including infections. Throughout the pandemic, multiple cases of rhabdomyolysis following COVID-19 infections have been reported. However, rhabdomyolysis subsequent to COVID-19 vaccinations appears to be relatively rare. Here, we report such a case after a second COVID-19 Comirnaty (BioNTech/Pfizer) vaccination. Our patient developed rhabdomyolysis 1 day after the second Comirnaty vaccination with high creatine kinase (CK) levels, generalized weakness, and kidney failure. CK levels and muscle weakness resolved after treatment with intravenous fluids, but unfortunately, he remained hemodialysis dependent after discharge. To our knowledge, this is one of the first case reports describing a patient with rhabdomyolysis after a Comirnaty vaccination. However, as millions of people have received the Comirnaty vaccine, it is unclear whether the rhabdomyolysis in our patient is a rare side effect or an unrelated, coincidental event. Large observational studies are needed to elucidate the causality between the Comirnaty vaccination and rhabdomyolysis. Awareness is warranted in patients with myalgia and muscle weakness shortly after COVID-19 vaccination, in order to initiate treatment early and prevent life-threatening complications.

Intravenous immunoglobulins as first-line treatment in idiopathic inflammatory myopathies: a pilot study

OBJECTIVES

We explored efficacy and safety of IVIg as first-line treatment in patients with an idiopathic inflammatory myopathy.

METHODS

In this investigator-initiated phase 2 open-label study, we included 20 adults with a newly diagnosed, biopsy-proven idiopathic inflammatory myopathy, and a disease duration of less than 9 months. Patients with IBM and prior use of immunosuppressants were excluded. The standard treatment regimen consisted of IVIg (Privigen) monotherapy for 9 weeks: a loading dose (2 g/kg body weight) and two subsequent maintenance doses (1 g/kg body weight) with a 3-week interval. The primary outcome was the number of patients with at least moderate improvement on the 2016 ACR/EULAR Total Improvement Score. Secondary outcomes included time to improvement, the number of patients requiring rescue medication and serious adverse events.

RESULTS

We included patients with DM (n = 9), immune-mediated necrotizing myopathy (n = 6), non-specific myositis/overlap myositis (n = 4) and anti-synthetase syndrome (n = 1). One patient was excluded from analyses because of minimal weakness resulting in a ceiling effect. Eight patients (8/19 = 42.0%; Clopper-Pearson 95% CI: 19.6, 64.6) had at least moderate improvement by 9 weeks. Of these, six reached improvement by 3 weeks. Seven patients required rescue medication due to insufficient efficacy and prematurely ended the study. Three serious adverse events occurred, of which one was pulmonary embolism.

CONCLUSION

First-line IVIg monotherapy led to at least moderate improvement in nearly half of patients with a fast clinical response in the majority of responders.

TRIAL REGISTRATION

Netherlands Trial Register identifier, NTR6160.

Biomarker profiles of endothelial activation and dysfunction in rare systemic autoimmune diseases: implications for cardiovascular risk

OBJECTIVES

Vasculopathy is an important hallmark of systemic chronic inflammatory connective tissue diseases (CICTD) and is associated with increased cardiovascular risk. We investigated disease-specific biomarker profiles associated with endothelial dysfunction, angiogenic homeostasis and (tissue) inflammation, and their relation to disease activity in rare CICTD.

METHODS

A total of 38 serum proteins associated with endothelial (dys)function and inflammation were measured by multiplex-immunoassay in treatment-naive patients with localized scleroderma (LoS, 30), eosinophilic fasciitis (EF, 8) or (juvenile) dermatomyositis (34), 119 (follow-up) samples during treatment, and 65 controls. Data were analysed by unsupervised clustering, Spearman correlations, non-parametric t test and ANOVA.

RESULTS

The systemic CICTD, EF and dermatomyositis, had distinct biomarker profiles, with 'signature' markers galectin-9 (dermatomyositis) and CCL4, CCL18, CXCL9, fetuin, fibronectin, galectin-1 and TSP-1 (EF). In LoS, CCL18, CXCL9 and CXCL10 were subtly increased. Furthermore, dermatomyositis and EF shared upregulation of markers related to interferon (CCL2, CXCL10), endothelial activation (VCAM-1), inhibition of angiogenesis (angiopoietin-2, sVEGFR-1) and inflammation/leucocyte chemo-attraction (CCL19, CXCL13, IL-18, YKL-40), as well as disturbance of the Angiopoietin-Tie receptor system and VEGF-VEGFR system. These profiles were related to disease activity, and largely normalized during treatment. However, a subgroup of CICTD patients showed continued elevation of CXCL10, CXCL13, galectin-9, IL-18, TNFR2, VCAM-1, and/or YKL-40 during clinically inactive disease, possibly indicating subclinical interferon-driven inflammation and/or endothelial dysfunction.

CONCLUSION

CICTD-specific biomarker profiles revealed an anti-angiogenic, interferon-driven environment during active disease, with incomplete normalization under treatment. This warrants further investigation into monitoring of vascular biomarkers during clinical follow-up, or targeted interventions to minimize cardiovascular risk in the long term.

Quantitative measurement of duplicated DNA as a diagnostic test for Charcot-Marie-Tooth disease type 1a

Charcot-Marie-Tooth disease type 1 (CMT1) is a hereditary motor and sensory neuropathy. The autosomal dominant subtype is often linked with a large duplication on chromosome 17p11.2. The gene encoding the peripheral myelin protein PMP 22 (the critical gene in this subtype of CMT1) is located within this duplication. To detect this duplication in chromosomal DNA from individuals thought to have CMT1, we compared the hybridization signals of two DNA probes within this duplication (VAW412R3a and VAW409R3a) with the signal of a reference probe (E3.9). When duplication was present, the signals from the first two probes increased from 100% (for nonduplicated samples) to 145% and 142%, respectively. The day-to-day variance was 3.7% and 5.1%, respectively. We demonstrated this DNA duplication in 49 of 95 DNA samples from unrelated individuals thought to have CMT1. Moreover, because hereditary neuropathy with liability to pressure palsies (HNPP) is based on a DNA deletion in the same area of chromosome 17, this quantitative test may be useful in establishing the presence of HNPP. In a preliminary investigation, four unrelated patients with HNPP yielded test values of 63% and 54%, respectively, of those for nonduplicated samples (CV 19% and 18%, respectively; n = 4), suggesting a deletion in 17p11.2.

Galectin-9 and CXCL10 as Biomarkers for Disease Activity in Juvenile Dermatomyositis: A Longitudinal Cohort Study and Multicohort Validation

Objective

Objective evaluation of disease activity is challenging in patients with juvenile dermatomyositis (DM) due to a lack of reliable biomarkers, but it is crucial to avoid both under‐ and overtreatment of patients. Recently, we identified 2 proteins, galectin‐9 and CXCL10, whose levels are highly correlated with the extent of juvenile DM disease activity. This study was undertaken to validate galectin‐9 and CXCL10 as biomarkers for disease activity in juvenile DM, and to assess their disease specificity and potency in predicting the occurrence of flares.

Methods

Levels of galectin‐9 and CXCL10 were measured by multiplex immunoassay in serum samples from 125 unique patients with juvenile DM in 3 international cross‐sectional cohorts and a local longitudinal cohort. The disease specificity of both proteins was examined in 50 adult patients with DM or nonspecific myositis (NSM) and 61 patients with other systemic autoimmune diseases.

Results

Both cross‐sectionally and longitudinally, galectin‐9 and CXCL10 outperformed the currently used laboratory marker, creatine kinase (CK), in distinguishing between juvenile DM patients with active disease and those in remission (area under the receiver operating characteristic curve [AUC] 0.86–0.90 for galectin‐9 and CXCL10; AUC 0.66–0.68 for CK). The sensitivity and specificity for active disease in juvenile DM was 0.84 and 0.92, respectively, for galectin‐9 and 0.87 and 1.00, respectively, for CXCL10. In 10 patients with juvenile DM who experienced a flare and were prospectively followed up, continuously elevated or rising biomarker levels suggested an imminent flare up to several months before the onset of symptoms, even in the absence of elevated CK levels. Galectin‐9 and CXCL10 distinguished between active disease and remission in adult patients with DM or NSM (P = 0.0126 for galectin‐9 and P < 0.0001 for CXCL10) and were suited for measurement in minimally invasive dried blood spots (healthy controls versus juvenile DM, P = 0.0040 for galectin‐9 and P < 0.0001 for CXCL10).

Conclusion

In this study, galectin‐9 and CXCL10 were validated as sensitive and reliable biomarkers for disease activity in juvenile DM. Implementation of these biomarkers into clinical practice as tools to monitor disease activity and guide treatment might facilitate personalized treatment strategies.

Effective cauda equina decompression in two siblings with Charcot-Marie-Tooth disease type 1B

Two siblings with Charcot-Marie-Tooth (CMT) 1B due to a c.517G>C (p.Gly173Arg) mutation in the MPZ gene both developed an acute cauda syndrome with unbearable back pain radiating to both legs, progressive muscle weakness of the legs, and saddle hypesthesia with fecal and urinary incontinence. MRI showed in both patients a lumbar spinal canal totally filled with hypertrophic caudal nerve roots. We performed acute decompression. Postoperatively, in both patients, the back pain resolved immediately, there was a significant improvement of both the paresis of the legs and the hypesthesia, and there was a full return of continence. There was no recurrence of acute symptoms during respectively 19 years and 1.5 years of follow-up. We conclude that in patients with CMT and a related cauda syndrome because of hypertrophic caudal nerve roots, acute decompression can be an effective and safe treatment with long-term efficacy.

Myositis with endomysial cell invasion indicates inclusion body myositis even if other criteria are not fulfilled

The objective of this study was to investigate if patients with endomysial mononuclear cell infiltrates invading non-necrotic fibers have a disease course consistent with inclusion body myositis (IBM), irrespective of other histopathological and clinical characteristics. All patients with a muscle biopsy showing endomysial inflammation with invasion of non-necrotic muscle fibers during the period 1979-2006 in two tertiary neuromuscular referral centers were classified into three groups: 1) patients whose biopsies also showed rimmed vacuoles; 2) patients whose biopsies showed no vacuoles but fulfilled clinical criteria for IBM, and 3) patients whose biopsies showed no vacuoles, and also did not fulfill clinical criteria for IBM (unclassified patients). These groups were compared with regard to age, gender, clinical features, and disease course including response to immunosuppressive treatment. Eighty-one individuals (41 men) were included. Rimmed vacuoles were found in 49 patients (60.5%). Fourteen patients (17.3%) fulfilled clinical criteria for IBM and 18 patients (22.2%) were unclassified at presentation. At follow up (mean duration 9 years) three women remained unclassified (4%). There were no differences in disease course or effect of treatment between the three groups. Men had more often rimmed vacuoles than women (73% vs 48%; p = 0.018), and women more often than men were unclassified. Women tended to show more often temporary improvement if treated (p = 0.07), but none had sustained improvement. In conclusion, patients with a muscle biopsy showing endomysial cell infiltration with invasion of non-necrotic muscle fibers most probably have IBM, regardless of clinical and other pathological features. Women lack typical features more often than men.

Recurrent and founder mutations in the Netherlands: the cardiac phenotype of DES founder mutations p.S13F and p.N342D

Background

Desmin-related myopathy (DRM) is an autosomally inherited skeletal and cardiac myopathy, mainly caused by dominant mutations in the desmin gene (DES). We describe new families carrying the p.S13F or p.N342D DES mutations, the cardiac phenotype of all carriers, and the founder effects.

Methods

We collected the clinical details of all carriers of p.S13F or p.N342D. The founder effects were studied using genealogy and haplotype analysis.

Results

We identified three new index patients carrying the p.S13F mutation and two new families carrying the p.N342D mutation. In total, we summarised the clinical details of 39 p.S13F carriers (eight index patients) and of 21 p.N342D carriers (three index patients). The cardiac phenotype of p.S13F carriers is fully penetrant and severe, characterised by cardiac conduction disease and cardiomyopathy, often with right ventricular involvement. Although muscle weakness is a prominent and presenting symptom in p.N342D carriers, their cardiac phenotype is similar to that of p.S13F carriers. The founder effects of p.S13F and p.N342D were demonstrated by genealogy and haplotype analysis.

Conclusion

DRM may occur as an apparently isolated cardiological disorder. The cardiac phenotypes of the DES founder mutations p.S13F and p.N342D are characterised by cardiac conduction disease and cardiomyopathy, often with right ventricular involvement.

Electronic supplementary material

The online version of this article (doi:10.1007/s12471-011-0233-y) contains supplementary material, which is available to authorized users.

Immunosuppressant and immunomodulatory treatment for dermatomyositis and polymyositis

BACKGROUND

Idiopathic inflammatory myopathies are chronic diseases with significant mortality and morbidity. Whilst immunosuppressive and immunomodulatory therapies are frequently used, the optimal therapeutic regimen remains unclear. This is an update of a review first published in 2005.

OBJECTIVES

To assess the effects of immunosuppressants and immunomodulatory treatments for dermatomyositis and polymyositis.

SEARCH METHODS

We searched the Cochrane Neuromuscular Disease Group Specialized Register (August 2011), the Cochrane Central Register of Controlled Trials (CENTRAL) (Issue 3 2011), MEDLINE (January 1966 to August 2011), EMBASE (January 1980 to August 2011) and clinicaltrials.gov (August 2011). We checked the bibliographies of identified trials and wrote to disease experts.

SELECTION CRITERIA

We included all randomised controlled trials (RCTs) or quasi-RCTs involving participants with probable or definite dermatomyositis and polymyositis as defined by the criteria of Bohan and Peter, or definite, probable or mild/early by the criteria of Dalakas. In participants without a classical rash of dermatomyositis, inclusion body myositis should have been excluded by muscle biopsy. We considered any immunosuppressant or immunomodulatory treatment. The two primary outcomes were the change in a function or disability scale measured as the proportion of participants improving one grade, two grades etc, predefined based on the scales used in the studies after at least six months, and a 15% or greater improvement in muscle strength compared with baseline after at least six months. Other outcomes were: the International Myositis Assessment and Clinical Studies Group (IMACS) definition of improvement, number of relapses and time to relapse, remission and time-to-remission, cumulative corticosteroid dose and serious adverse effects.

DATA COLLECTION AND ANALYSIS

Two authors independently selected papers, extracted data and assessed risk of bias in included studies. They collected adverse event data from the included studies.

MAIN RESULTS

The review authors identified fourteen 14 relevant RCTs. They excluded four trials.The 10 included studies, four of which have been added in this update, included a total of 258 participants. Six studies compared an immunosuppressant or immunomodulator with placebo control, and four studies compared two immunosuppressant regimes with each other. Most of the studies were small (the largest had 62 participants) and many of the reports contained insufficient information to assess risk of bias.Amongst the six studies comparing immunosuppressant with placebo, one study, investigating intravenous immunoglobulin (IVIg), showed statistically significant improvement in scores of muscle strength in the IVIg group over three months. Another study investigating etanercept showed some evidence of a steroid sparing effect, a secondary outcome in this review, but no improvement in other assessed outcomes. The other four randomised placebo-controlled trials assessed either plasma exchange and leukapheresis, eculizumab, infliximab or azathioprine against placebo and all produced negative results.Three of the four studies comparing two immunosuppressant regimes (azathioprine with methotrexate, ciclosporin with methotrexate, and intramuscular methotrexate with oral methotrexate plus azathioprine) showed no statistically significant difference in efficacy between the treatment regimes. The fourth study comparing pulsed oral dexamethasone with daily oral prednisolone and found that the dexamethasone regime had a shorter median time to relapse but fewer side effects.Immunosuppressants were associated with significant side effects.

AUTHORS' CONCLUSIONS

This systematic review highlights the lack of high quality RCTs that assess the efficacy and toxicity of immunosuppressants in inflammatory myositis.

WITHDRAWN: Immunosuppressant and immunomodulatory treatment for dermatomyositis and polymyositis

BACKGROUND

Idiopathic inflammatory myopathies are chronic skeletal diseases with significant mortality and morbidity despite treatment by corticosteroids. Immunosuppressive agents and immunomodulatory therapy are used to improve disease control and reduce the long-term side effects of corticosteroids. While these treatments are used commonly in routine clinical practice, the optimal therapeutic regimen remains unclear.

OBJECTIVES

To systematically review the evidence for the effectiveness of immunosuppressants and immunomodulatory treatments for dermatomyositis and polymyositis.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group trials register (searched February 2002 and updated in November 2003) and MEDLINE (January 1966 to December 2002). We checked bibliographies of identified trials and wrote to disease experts.

SELECTION CRITERIA

Randomised or quasi-randomised controlled trials including patients with probable or definite dermatomyositis and polymyositis as defined by the criteria of Bohan and Peter or definite, probable or mild/early by the criteria of Dalakas. Patients with inclusion body myositis should have been excluded by muscle biopsies. Any immunosuppressant or immunomodulatory treatment including corticosteroids, azathioprine, methotrexate, ciclosporin, chlorambucil, cyclophosphamide, intravenous immunoglobulin, interferon and plasma exchange was considered. Primary outcome was assessment of muscle strength after at least six months. Other outcomes were: change in disability, number of relapses and time to relapse, number of patients in remission and time-to-remission, cumulative corticosteroid dose and serious adverse effects.

DATA COLLECTION AND ANALYSIS

Two authors (EC and JH) independently selected trials for inclusion in the review. Four authors independently assessed each study. Methodological criteria and the results of each study were recorded on data extraction forms.

MAIN RESULTS

Seven potentially relevant randomised controlled trials were identified. One trial was excluded. Three studies compared immunosuppressant with placebo control, one trial compared one immunosuppressant (methotrexate) with another (azathioprine), another trial compared ciclosporin A with methotrexate and the final trial compared intramuscular methotrexate with oral methotrexate plus azathioprine. The study comparing intravenous immunoglobulin with placebo concluded that the former was superior. Two randomised placebo-controlled trials assessing plasma exchange, leukapheresis and azathioprine produced negative results. The fourth study compared azathioprine with methotrexate and found azathioprine and methotrexate equally effective but methotrexate had a better side effect profile. The fifth study comparing ciclosporin A with methotrexate and the sixth study comparing intramuscular methotrexate with oral methotrexate plus azathioprine found no statistically significant differences between the treatment groups. Immunosuppressants are associated with significant side effects.

AUTHORS' CONCLUSIONS

This systematic review highlights the lack of high quality randomised controlled trials that assess the efficacy and toxicity of immunosuppressants in inflammatory myositis.

Spontaneous recovery of dermatomyositis and unspecified myositis in three adult patients

Dermatomyositis (DM), polymyositis and unspecified myositis are idiopathic inflammatory myopathies in which prednisone is usually started as soon as the diagnosis has been established. Therefore, little is known about the natural history of these diseases and spontaneous recovery may escape attention. Here, we present three patients who achieved remission without administration of immunosuppressants. In these three patients, treatment was not started because of spontaneously improving symptoms and signs during the diagnostic process. After 3-5 years, all patients are still free of muscle weakness. These case reports demonstrate that spontaneous long lasting remission can occur in a small proportion of patients with subacute onset idiopathic inflammatory myopathies. In some patients, immunosuppressive treatment with the risk of serious side effects can perhaps be omitted. However, close and frequent monitoring is required in these instances.

Long-term outcome in polymyositis and dermatomyositis

BACKGROUND

Although polymyositis and dermatomyositis are regarded as treatable disorders, prognosis is not well known, as in the literature long-term outcome and prognostic factors vary widely.

AIM

To analyse the prognostic outcome factors in polymyositis and adult dermatomyositis.

METHODS

We determined mortality, clinical outcome (muscle strength, disability, persistent use of drugs and quality of life) and disease course and analysed prognostic outcome factors.

RESULTS

Disease-related death occurred in at least 10% of the patients, mainly because of associated cancer and pulmonary complications. Re-examination of 110 patients after a median follow-up of 5 years showed that 20% remained in remission and were off drugs, whereas 80% had a polycyclic or chronic continuous course. The cumulative risk of incident connective tissue disorder in patients with myositis was significantly increased. 65% of the patients had normal strength at follow-up, 34% had no or slight disability, and 16% had normal physical sickness impact profile scores. Muscle weakness was associated with higher age (odds ratio (OR) 3.6; 95% confidence interval (CI) 1.3 to 10.3). Disability was associated with male sex (OR 3.1; 95% CI 1.2 to 7.9). 41% of the patients with a favourable clinical outcome were still using drugs. Jo-1 antibodies predicted the persistent use of drugs (OR 4.4, 95% CI 1.3 to 15.0).

CONCLUSIONS

Dermatomyositis and polymyositis are serious diseases with a disease-related mortality of at least 10%. In the long term, myositis has a major effect on perceived disability and quality of life, despite the regained muscle strength.

Late onset axonal Charcot-Marie-Tooth phenotype caused by a novel myelin protein zero mutation

A late onset axonal Charcot-Marie-Tooth phenotype is described, resulting from a novel mutation in the myelin protein zero (MPZ) gene. Comparative computer modelling of the three dimensional structure of the MPZ protein predicts that this mutation does not cause a significant structural change. The primary axonal disease process in these patients points to a function of MPZ in maintenance of the myelinated axons, apart from securing stability of the myelin layer.

[The practice guideline 'Dermatomyositis, polymyositis and sporadic inclusion body myositis']

This guideline presents recommendations for the diagnosis and treatment of dermatomyositis, polymyositis and sporadic inclusion body myositis (sIBM) according to the best available evidence. Characteristic skin abnormalities can be sufficient for the diagnosis of dermatomyositis. In case of doubt, a skin biopsy is advisable. A muscle biopsy is indicated when other examinations are inconclusive and the musculature is involved. The working group considers screening for cancer to be required in adults with dermatomyositis and presents recommendations for the way that this should be done. At least one-third of all patients with polymyositis has, or will develop, an associated inflammatory connective tissue disease. If a patient with a connective tissue disease develops symmetrical, proximal muscle weakness in the course of weeks or months, this may be assumed to be due to polymyositis. In the absence ofpre-existing connective tissue disease, demonstration of a mononuclear cell infiltrate in muscle tissue is a prerequisite for the diagnosis ofpolymyositis. The histopathology of muscle tissue is used as the gold standard for the diagnosis of sIBM. The practice guideline presents criteria for the concept 'activity' of myositis. Disease activity serves as a guideline for the treatment of polymyositis and dermatomyositis. The treatment of choice for dermatomyositis and polymyositis is high-dose prednisone. Physical activity does not have a negative effect on the course of these diseases. The long-term prognosis ofdermatomyositis and polymyositis is not well known. The clinical course of sIBM is slowly progressive.

Associations with autoimmune disorders and HLA class I and II antigens in inclusion body myositis

Whether autoimmune mechanisms play a role in the pathogenesis of inclusion body myositis (IBM) is unknown. Human leukocyte antigen (HLA) analysis in 52 patients, including 17 with autoimmune disorders (AIDs), showed that patients were more likely to have antigens from the autoimmune-prone HLA-B8-DR3 ancestral haplotype than healthy control subjects, irrespective of the presence of AIDs. Patients lacked the apparently protective HLA-DR53 antigen. The results provide further support for an autoimmune basis in IBM.

Immunosuppressant and immunomodulatory treatment for dermatomyositis and polymyositis

BACKGROUND

Idiopathic inflammatory myopathies are chronic skeletal diseases with significant mortality and morbidity despite treatment by corticosteroids. Immunosuppressive agents and immunomodulatory therapy are used to improve disease control and reduce the long-term side effects of corticosteroids. While these treatments are used commonly in routine clinical practice, the optimal therapeutic regimen remains unclear.

OBJECTIVES

To systematically review the evidence for the effectiveness of immunosuppressants and immunomodulatory treatments for dermatomyositis and polymyositis.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group trials register (searched February 2002 and updated in November 2003) and MEDLINE (January 1966 to December 2002). We checked bibliographies of identified trials and wrote to disease experts.

SELECTION CRITERIA

Randomised or quasi-randomised controlled trials including patients with probable or definite dermatomyositis and polymyositis as defined by the criteria of Bohan and Peter or definite, probable or mild/early by the criteria of Dalakas. Patients with inclusion body myositis should have been excluded by muscle biopsies. Any immunosuppressant or immunomodulatory treatment including corticosteroids, azathioprine, methotrexate, ciclosporin, chlorambucil, cyclophosphamide, intravenous immunoglobulin, interferon and plasma exchange was considered. Primary outcome was assessment of muscle strength after at least six months. Other outcomes were: change in disability, number of relapses and time to relapse, number of patients in remission and time-to-remission, cumulative corticosteroid dose and serious adverse effects.

DATA COLLECTION AND ANALYSIS

Two authors (EC and JH) independently selected trials for inclusion in the review. Four authors independently assessed each study. Methodological criteria and the results of each study were recorded on data extraction forms.

MAIN RESULTS

Seven potentially relevant randomised controlled trials were identified. One trial was excluded. Three studies compared immunosuppressant with placebo control, one trial compared one immunosuppressant (methotrexate) with another (azathioprine), another trial compared ciclosporin A with methotrexate and the final trial compared intramuscular methotrexate with oral methotrexate plus azathioprine. The study comparing intravenous immunoglobulin with placebo concluded that the former was superior. Two randomised placebo-controlled trials assessing plasma exchange, leukapheresis and azathioprine produced negative results. The fourth study compared azathioprine with methotrexate and found azathioprine and methotrexate equally effective but methotrexate had a better side effect profile. The fifth study comparing ciclosporin A with methotrexate and the sixth study comparing intramuscular methotrexate with oral methotrexate plus azathioprine found no statistically significant differences between the treatment groups. Immunosuppressants are associated with significant side effects.

AUTHORS' CONCLUSIONS

This systematic review highlights the lack of high quality randomised controlled trials that assess the efficacy and toxicity of immunosuppressants in inflammatory myositis.

Inclusion body myositis

The clinical features of inclusion body myositis (IBM) were of minor importance in the design of consensus diagnostic criteria, mainly because of controversial views on the specificity of signs and symptoms, although some authors reported "typical" signs. To re-assess the clinical spectrum of IBM, a single investigator using a standard protocol studied a cohort of 64 patients cross-sectionally. Symptom onset was before the age of 50 years in 20% of cases. Only a few patients (14 %) started with weakness other than that of quadriceps, finger flexor or pharyngeal muscles. The sequence of power loss was erratic, but onset of symptoms with quadriceps weakness predicted an earlier onset of dysphagia in older patients (> or = 56 years) compared with younger ones (< 56 years) (p = 0.02). Despite widespread weakness patients had favourable scores on three commonly used function scales and they kept their employment. Complete wheel-chair dependency was rare (3 %). A dominant characteristic was the anatomical distribution of afflicted muscles: ventral extremity muscle groups were more affected than dorsal muscle groups and girdle muscles were least affected, the latter preserving postural stability. Ankylosis, especially in extension of the fingers,was frequently present. Together with the sparing of intrinsic hand muscles it was helpful in the preservation of many skillful movements. IBM has a unique distribution of muscle weakness. Ankylotic contractures are common. We feel that their joint impact on daily functioning is characteristic for the disease.

Follow up of patients with signs and symptoms of polyneuropathy not confirmed by electrophysiological studies

The outcome and final diagnoses of patients with symptoms and/or signs suggestive of polyneuropathy, but with normal electrophysiological studies, were investigated. All patients who presented at the outpatient clinic between 1993 and 1998 with signs and symptoms suggestive of polyneuropathy, but in whom electrophysiological studies were normal, were included. We retrospectively collected data from the medical records and then interviewed the patients and used the Sickness Impact Profile scale to investigate functional status at least 2 years after presentation. We included 74 patients, of whom 39 had neurological signs at neurological examination at the first visit. A final diagnosis was made in 24 of the 39 patients with neurological signs, and in three of the 35 patients without neurological signs but with symptoms. One (3%) of the 35 patients without neurological signs at the first visit had a poor outcome versus 15 (39%) of the 39 patients with neurological signs. In 11 (41%) of the 27 patients in the group with a final diagnosis the outcome was poor versus 5 (11%) of 47 patients without a final diagnosis. In 11 patients we concluded that they probably had small fibre neuropathy. Patients presenting with symptoms of polyneuropathy but who have neither neurological signs of polyneuropathy nor electrophysiological studies confirming a polyneuropathy have a good outcome at least 2 years after presentation. Further investigations are not indicated, except for patients fulfilling the criteria of small fibre neuropathy. In patients with neurological signs, as the outcome depends on the diagnosis and an explanation for these signs is often found, repeated investigations in this group are mandatory.

Polymyositis: an ongoing discussion about a disease entity

Since its first description more than a century ago, there has been much debate about the diagnostic entity polymyositis. Because initial observations were of individuals with dermatomyositis, it appeared that polymyositis was not possible without skin lesions. Distinctive clinical and histologic features of polymyositis were not established until the late 20th century. The identification of inclusion body myositis as a distinct entity has further refined nosographic classification.

Polymyositis: an overdiagnosed entity

BACKGROUND

According to widely used criteria (Bohan and Peter criteria, 1975), dermatomyositis (DM) is differentiated from polymyositis (PM) only by skin changes. More recent criteria also include histopathologic characteristics enabling the distinction between PM and DM and the differentiation of sporadic inclusion body myositis (s-IBM) from PM. The authors investigated the applicability of diagnostic features for diagnosing PM and DM.

METHODS

The authors performed a retrospective follow-up study of 165 patients with 1) a previous diagnosis of myositis; 2) subacute onset of symmetric, proximal weakness; and 3) an evaluation between 1977 and 1998 excluding other neuromuscular disorders.

RESULTS

The diagnoses at initial evaluation based on clinical, laboratory, and histopathologic criteria were PM, 9 (5%); DM, 59 (36%; 54 isolated, 3 with associated connective tissue disease [CTD], 2 with associated malignancy); unspecified myositis (perimysial/perivascular infiltrates, no PM or DM), 65 (39%; 38 isolated myositis, 26 with associated CTD, 1 with malignancy); and possible myositis (necrotizing myopathy, no inflammatory infiltrates), 32 (19%; 29 isolated myositis, 3 with associated CTD). At follow-up evaluation, five of the nine patients with PM had typical s-IBM features. None of the remaining four patients complied with the assumed typical signs of PM. Ten of the 38 patients with isolated unspecified myositis had been diagnosed with a CTD.

CONCLUSIONS

Polymyositis is an overdiagnosed entity. At evaluation, more than half the patients with autoimmune myositis cannot be specifically diagnosed with polymyositis or dermatomyositis. A quarter of patients with isolated unspecified myositis subsequently developed connective tissue disease.

Necrotising myopathy, an unusual presentation of a steroid-responsive myopathy

OBJECTIVE

To evaluate the clinical features, muscle pathology and response to treatment in patients with a necrotising myopathy, without mononuclear cell infiltrates.

BACKGROUND

Mononuclear cell infiltrates in the muscle biopsy specimen are the diagnostic hallmark of the immune-mediated idiopathic inflammatory myopathies (IIM). In patients with the typical clinical features of IIM, absence of these infiltrates in the muscle biopsy specimen casts doubt on the diagnosis and leads to uncertainty about therapeutical strategies.

METHODS

A detailed description is given of the clinical, laboratory, and histopathological features of eight patients suspected of having an idiopathic inflammatory myopathy, in whom mononuclear cell infiltrates in their muscle biopsy specimens were lacking.

RESULTS

Eight patients (five men, three women, age range 40-69 years) had severe, symmetrical proximal weakness with a subacute onset. There were no skin abnormalities suggesting dermatomyositis. Serum creatine kinase activity was more than 10 times elevated. Repeated muscle biopsy specimens, taken from a symptomatic muscle prior to immunosuppressive treatment showed widespread necrosis, regeneration, and atrophy of muscle fibres, but no mononuclear cell infiltrates. Known causes of necrotising myopathy were excluded. Three patients had a malignancy. Adequately dosed and sustained immunosuppressive treatment eventually resulted in normal or near normal muscle strength in seven patients. One patient showed marked improvement.

CONCLUSION

Occasionally, patients who clinically present as an idiopathic inflammatory myopathy may lack mononuclear cell infiltrates in their muscle biopsy specimens. This subacute-onset progressive necrotising myopathy should not deter the clinician from timely and appropriate treatment as we consider this myopathy to be steroid-responsive with a possible immune-mediated pathogenesis.

Evidence for heterogeneity of T cell expansion in polymyositis and inclusion body myositis

Vbeta usage of muscle-infiltrating T lymphocytes in polymyositis (PM) and sporadic inclusion body myositis (s-IBM) was correlated with clinical and histopathological features. Immunohistochemical analysis was combined with complementarity-determining region 3 (CDR3) length analysis in nine muscle biopsies of eight PM patients and six biopsies of five s-IBM patients. Vbeta usage was heterogeneous in seven patients. Four of these patients had definite PM with endomysial located T cell infiltrates, but T cells specifically surrounding and invading individual non-necrotic fibers were not found. In two s-IBM patients, Vbeta 2 usage was increased. In one of them, a repeat biopsy showed a heterogeneous Vbeta usage. We conclude that clonal expansion of muscle-infiltrating T cells could only be detected in part of the patients. Explanations may be that clonal expansion does not take place in all disease phases and that PM is a heterogeneous disease with respect to pathogenesis.

[Three patients with divergent presentations of idiopathic inflammatory myopathy]

The group of idiopathic inflammatory myopathies encompasses polymyositis, dermatomyositis and inclusion body myositis. These diseases share the following features: progressive muscle weakness, an increase in serum creatine kinase activity and the presence of mononuclear cell infiltrates in the muscle biopsy. Polymyositis, dermatomyositis and inclusion body myositis are differentiated on the basis of the distribution of muscle weakness, and specific histopathological features. Many specialties may see these patients as the clinical presentation can vary widely and may be atypical, requiring further diagnostic procedures. A 40-year-old man with a heliotrope rash and periorbital oedema, but no muscle involvement, was diagnosed with dermatomyositis sine myositis. He was successfully treated with corticosteroids but died later of cardiac failure. A 72-year-old man with a pulmonary malignancy subsequently developed the clinical features of dermatomyositis. Steroid therapy diminished the complaints but he died of pulmonary embolism. A 54-year-old woman with the clinical features of inclusion body myositis did not have rimmed vacuoles in her muscle biopsy specimen and was initially erroneously diagnosed with polymyositis, for which she was treated with corticosteroids, but without beneficial effect.

Comparison of weakness progression in inclusion body myositis during treatment with methotrexate or placebo

We investigated whether 5 to 20mg per week oral methotrexate could slow down disease progression in 44 patients with inclusion body myositis in a randomized double-blind placebo-controlled study over 48 weeks. Mean change of quantitative muscle strength testing sum scores was the primary study outcome measure. Quantitative muscle strength testing sum scores declined in both treatment groups, -0.2% for methotrexate and -3.4% for placebo (95% confidence interval = -2.5% to +9.1% for difference). There were also no differences in manual muscle testing sum scores, activity scale scores and patients' own assessments after 48 weeks of treatment. Serum creatine kinase activity decreased significantly in the methotrexate group. We conclude that oral methotrexate did not slow down progression of muscle weakness but decreased serum creatine kinase activity.

Rimmed vacuoles and the added value of SMI-31 staining in diagnosing sporadic inclusion body myositis

Problems in diagnosing sporadic inclusion body myositis may arise if all clinical features fit a diagnosis of polymyositis, but the muscle biopsy shows some rimmed vacuoles. Recently, immunohistochemistry with an antibody directed against phosphorylated neurofilament (SMI-31) has been advocated as a diagnostic test for sporadic inclusion body myositis. The aims of the present study were to define a quantitative criterion to differentiate sporadic inclusion body myositis from polymyositis based on the detection of rimmed vacuoles in the haematoxylin-eosin staining and to evaluate the additional diagnostic value of the SMI-31 staining. Based on clinical criteria and creatine kinase levels in patients with endomysial infiltrates, 18 patients complied with the diagnosis of sporadic inclusion body myositis, and 17 with the diagnosis of polymyositis. A blinded observer counted the abnormal fibres in haematoxylin-eosin-stained sections and in SMI-31-stained sections. The optimal cut-off in the haematoxylin-eosin test was 0.3% vacuolated fibres. Adding the SMI-31 staining significantly increased the positive predictive value from 87 to 100%, but increased the negative predictive value only to small extent. We conclude that (1) patients with clinical and laboratory features of polymyositis, including response to treatment, may show rimmed vacuoles in their muscle biopsy and that (2) adding the SMI-31 stain can be helpful in differentiating patients who respond to treatment from patients who do not.

Oral pulsed high-dose dexamethasone for myositis

To study the short-term effect of oral pulsed high-dose dexamethasone for myositis we treated eight newly diagnosed patients with three 28-day cycles of oral dexamethasone. Primary outcome measures were muscle strength, pain, and serum creatine kinase activity. Six patients responded. Side effects were mild. At follow-up five responders were still in remission, without medication. Pulsed high-dose dexamethasone seems beneficial in myositis. A larger, prednisone-controlled trial is justified to analyze long-term efficacy.

Absence of characteristic features in two patients with inclusion body myositis

According to recently published criteria a diagnosis of definite sporadic inclusion body myositis is made if the typical histopathological abnormalities (rimmed vacuoles and abnormal accumulations of proteins, in addition to mononuclear cell infiltrates) are present. The two women described here presented with myositis which was unresponsive to treatment. Patient 1 had features of non-progressive sporadic inclusion body myositis clinically, whereas patient 2 had a very slowly progressive limb girdle syndrome. The cryostat sections of the first biopsies did not show rimmed vacuoles, even in retrospect. Only a repeated biopsy, 12 years after presentation in one patient and 18 years after presentation in the other, disclosed the typical features of sporadic inclusion body myositis. The initial absence of abnormal fibres probably represents a real absence or scarcity rather then a sampling error due to a multifocal nature of the histological abnormalities. It is of importance for the clinician to realise that some patients with myositis unresponsive to treatment, even if both clinical and histological features do not suggest sporadic inclusion body myositis, may prove to have the disease on repeated histopathological examination.

Connexin32 gene mutations in X-linked dominant Charcot-Marie-Tooth disease (CMTX1)

Single-strand conformational polymorphisms (SSCP) of the connexin32 gene were analyzed in 121 patients possibly affected by Charcot-Marie-Tooth (CMT) disease. The 121 patients were selected from 443 possible CMT/HNPP (hereditary neuropathy with liability to pressure palsies) patients based on genetic linkage to Xq13.1, absence of the 17p12 duplication and deletion, and absence of point mutations in PMP22 and P0. We found five new mutations at nucleotides 105 (C-T), 316 (C-G), 321 (C-T), 328 (T-C), and 657 (G-C), and three mutations at nucleotide 126 (C-T), 249 (G-A), and 477 (G-A) previously described in other unrelated families. The nucleotide changes resulted in seven amino-acid substitutions and one premature stop codon.

Inherited demyelinating peripheral neuropathies: relating myelin packing abnormalities to P0 molecular defects

P0-glycoprotein, the major integral membrane protein of peripheral nerve myelin, is thought to mediate myelination and membrane interactions via its extracellular domain (P0-ED). Molecular modeling of P0-ED has suggested which of its amino acid side-chains may be involved in heterophilic and homophilic adhesions. We previously showed that some of these amino acids are the same ones that are substituted or deleted due to mutations in the human gene for P0 (MPZ), which correlate with certain cases of demyelinating motor and sensory peripheral neuropathies. In the current study, high magnification electron microscopy was used to examine the myelin membrane packing in sural nerve biopsies from patients with MPZ mutations. We found that there were distinguishable ultrastructural phenotypes that could be explained by the alterations in P0-ED. These phenotypes, which were not observed in a control nerve, included widening or irregularity of the extracellular apposition alone (delta Ser34; Arg69Cys), widening at both the extracellular and cytoplasmic appositions (Arg69His), the presence of focal bridges in the widened extracellular space (Arg69His), and a diminished (Arg69Cys) or absence (Arg69His) of staining of the double intraperiod line. Our study, which suggests that the altered P0 is incorporated into the myelin sheath, provides a unique basis for further molecular/ultrastructural correlations between P0-ED structure and myelination irregularities.

Peripheral neuropathy in mice transgenic for a human MDR3 P-glycoprotein mini-gene

We have generated mice transgenic for a human MDR3 mini-gene, under control of a hamster vimentin promoter. Expression of the MDR3 transgene was found in mesenchymal tissues, peripheral nerves, and the eye lens. These MDR3 transgenic mice have a slowed motor nerve conduction and dysmyelination of their peripheral nerves. An extensive dysmyelination in some transgenic strains results in a severe peripheral neuropathy with paresis of the hind legs. How expression of the MDR3 transgene causes these abnormalities is unknown. The MDR3 gene encodes a large glycosylated plasma membrane protein with multiple transmembrane spanning domains, which are involved in the translocation of the phospholipid phosphatidylcholine through the hepatocyte canalicular membrane. The ability of the MDR3 P-glycoprotein to alter phsopholipid distribution in the plasma membrane of Schwann cells may cause the damage. It is also possible, however, that the presence of a large glycoprotein in the cell membrane may be sufficient to severely disturb myelination of peripheral nerves.

Clinically distinct codon 69 mutations in major myelin protein zero in demyelinating neuropathies

Mutations in the major peripheral myelin protein zero (P0) gene on chromosome 1q21-q23 have been found with the hereditary demyelinating polyneuropathy Charcot-Marie-Tooth type 1B. Here, we describe 2 patients with distinct neurological characteristics, carrying different substitutions at the same codon--Arg69His and Arg69Cys. The patients were heterozygous for the mutation, which in both appeared to be de novo. Histological examination of sural nerve biopsy specimens revealed defective myelin as well as marked differences, confirming the importance of P0 in the compaction of myelin.

Two divergent types of nerve pathology in patients with different P0 mutations in Charcot-Marie-Tooth disease

In seven unrelated patients with a demyelinating motor and sensory neuropathy, we found mutations in exons 2 and 3 of the P0 gene. Morphologic examination of sural nerve biopsy specimens showed a demyelinating process with onion bulb formation in all cases. In four patients, ultrastructural examination demonstrated uncompacted myelin in 23 to 68% of the myelinated fibers, which is in agreement with the widely accepted function of P0 as a homophilic adhesion molecule. Three patients showed normal compact myelin, but morphology was dominated by the abundant occurrence of focally folded myelin. The two divergent pathologic phenotypes exemplify that some mutations act differently on P0 protein formation or function than others, which is probably determined by site and nature of the mutation in the P0 gene.

Charcot-Marie-Tooth disease type 1A: morphological phenotype of the 17p duplication versus PMP22 point mutations

Charcot-Marie-Tooth disease type 1A (CMT1A) or hereditary motor and sensory neuropathy type Ia (HMSN type Ia) is an autosomal dominant demyelinating polyneuropathy, which may result from duplications as large as 1.5 Mb on chromosome 17p 11.2-p12 encompassing the gene for the peripheral myelin protein PMP22, or from point mutations in this gene. In general, it is not possible to distinguish, by clinical and neurophysiological criteria, the cases associated with the duplication mutation from those associated with point mutations of the PMP22 gene, although the latter tend to be more severe. In this study we demonstrated that the two genotypes exhibit different morphological characteristics. In the PMP22 duplicated cases the mean g-ratio (axon diameter versus fibre diameter) is significantly lower than normal, while in cases of PMP22 point mutations nearly all myelinated fibers have an extremely high g-ratio. In cases with point mutations, onion bulbs are abundantly present from an early age, whereas onion bulbs in the duplicated cases develop gradually in the first years of life. Increase in total transverse fascicular area is most pronounced in the point mutation cases. The differences in pathology between these two very different types of mutations involving the same gene likely reflect differences in pathogenesis and may offer clues in understanding the function of PMP22.

Hereditary motor and sensory neuropathy type I: clinical and neurographical features of the 17p duplication subtype

Forty-four affected individuals, aged 8-68 years (mean 34 years), from six families with hereditary motor and sensory neuropathy type I (HMSN I, Charcot-Marie-Tooth disease type 1) were investigated to determine the clinical and electroneurographical characteristics of the HMSN I subtype that is defined by the presence of a DNA duplication on chromosome 17p. Motor nerve conduction velocity (MNCV) and, to a lesser extent, compound muscle action potential amplitude, were inversely related to clinical severity. Neither clinical severity nor MNCV were significantly related to age. These results suggest that the primary pathological process is not, or only slightly active after childhood.

Chronic inflammatory demyelinating polyneuropathy or hereditary motor and sensory neuropathy? Diagnostic value of morphological criteria

The pathological changes generally considered to distinguish chronic inflammatory demyelinating polyneuropathy (CIDP) from hereditary motor and sensory neuropathy (HMSN) are: mononuclear cell infiltrates, prominent endoneurial oedema, and marked fascicle-to-fascicle variability. We evaluated the diagnostic significance of these pathological features which are suggestive of CIDP. Nerve biopsies from 42 dominant HMSN type I cases with a normal disease course were investigated for the occurrence of inflammatory features. A small cluster of mononuclear cells was found in 12% of the cases and marked endoneurial oedema in 21%. Variability in pathology between the fascicles was not observed. The histogram configuration yielded additional information for differential diagnosis. Subsequently, we reviewed the clinical, electrophysiological and morphological features of 18 sporadic cases of chronic progressive demyelinating motor and sensory neuropathy with mainly classic onion bulbs in their nerve biopsies and a disease onset in the first decade. In all these patients DNA investigation for the 17p11.2 duplication was performed. According to the results of the DNA investigation, autosomal dominant HMSN type Ia was diagnosed in eight patients, although in six slight 'CIDP-positive' features were present. A diagnosis was definite or most probable CIDP in eight patients. In two patients no definite diagnosis could be made. Testing for the presence of the 17p11.2 duplication is, therefore, helpful in distinguishing between CIDP and HMSN type I. The diagnosis of CIDP requires careful evaluation of the clinical, electrophysiological and morphological data to avoid false-positive diagnoses of inflammatory disorders.

Quantitative measurement of duplicated DNA as a diagnostic test for Charcot-Marie-Tooth disease type 1a

Charcot-Marie-Tooth disease type 1 (CMT1) is a hereditary motor and sensory neuropathy. The autosomal dominant subtype is often linked with a large duplication on chromosome 17p11.2. The gene encoding the peripheral myelin protein PMP 22 (the critical gene in this subtype of CMT1) is located within this duplication. To detect this duplication in chromosomal DNA from individuals thought to have CMT1, we compared the hybridization signals of two DNA probes within this duplication (VAW412R3a and VAW409R3a) with the signal of a reference probe (E3.9). When duplication was present, the signals from the first two probes increased from 100% (for nonduplicated samples) to 145% and 142%, respectively. The day-to-day variance was 3.7% and 5.1%, respectively. We demonstrated this DNA duplication in 49 of 95 DNA samples from unrelated individuals thought to have CMT1. Moreover, because hereditary neuropathy with liability to pressure palsies (HNPP) is based on a DNA deletion in the same area of chromosome 17, this quantitative test may be useful in establishing the presence of HNPP. In a preliminary investigation, four unrelated patients with HNPP yielded test values of 63% and 54%, respectively, of those for nonduplicated samples (CV 19% and 18%, respectively; n = 4), suggesting a deletion in 17p11.2.

Deletion of the serine 34 codon from the major peripheral myelin protein P0 gene in Charcot-Marie-Tooth disease type 1B

Charcot-Marie-Tooth disease type 1B (CMT1B) is genetically linked to chromosome 1q21-23. The major peripheral myelin protein gene, P0, has been cloned and localized to the same chromosomal region. P0 is a 28 kDa glycoprotein involved in the compaction of the multilamellar myelin sheet and accounts for more than half of the peripheral myelin protein content. We checked whether P0 is altered in CMT1B, and show here that a 3 basepair deletion in exon 2 of the P0 gene is present in all affected individuals of a CMT1B family. The mutation results in the deletion of serine 34 in the extracellular domain of P0, suggesting that alterations of P0 cause CMT1B.

Allelic heterogeneity in hereditary motor and sensory neuropathy type Ia (Charcot-Marie-Tooth disease type 1a)

The most frequently found mutation in autosomal dominant hereditary motor and sensory neuropathy type I (HMSN I) is a large duplication on chromosome 17p11.2 containing probes VAW409R3, VAW412R3, and EW401. We investigated a family with severe features of HMSN I, and demonstrated the absence of this duplication by a quantitative analysis of the hybridization signals of VAW409R3 and VAW412R3. Linkage analysis, however, revealed linkage with probe VAW409R3a (lod score, 3.22), which demonstrates the existence of allelic heterogeneity within the HMSN Ia locus. These findings have implications for clinical practice and for investigating the identity of the HMSN Ia gene.

Identical point mutations of PMP-22 in Trembler-J mouse and Charcot-Marie-Tooth disease type 1A

We have investigated the peripheral myelin protein gene, PMP-22, in a family with Charcot-Marie-Tooth disease type 1A (CMT1A). The DNA duplication commonly found in CMT1A was absent in this family, but strong linkage existed between the disease and the CMT1A marker VAW409R3 on chromosome 17p11.2. We found a point mutation in PMP-22 which was completely linked with the disease. The mutation, a proline for leucine substitution in the first putative transmembrane domain, is identical to that recently found in the Trembler-J mouse. The presence of this PMP-22 defect in this CMT1A family and the location of PMP-22 within the DNA duplication associated with CMT1A suggest that both structural alteration and overexpression of PMP-22 may lead to the disease.

The peripheral myelin gene PMP-22/GAS-3 is duplicated in Charcot-Marie-Tooth disease type 1A

Charcot-Marie-Tooth disease type 1A (CMT1A) is associated with a DNA duplication at chromosome 17p11.2. In view of the point mutation in the gene for peripheral myelin protein pmp-22/gas-3 in Trembler mice, a murine model for CMT1A, we have analysed whether this gene is altered in CMT1A. Here we show that the human homologue of the murine pmp-22 gene is located within the CMT1A DNA duplication, which is a direct repeat and does not interrupt the coding region of PMP-22. Expression of PMP-22 in CMT1A fibroblasts is similar to expression in control fibroblasts. Increased gene dosage or altered PMP-22 expression in the peripheral nervous system are therefore possible mechanisms by which PMP-22 is involved in CMT1A.