Hereditary complement (C9) deficiency associated with dermatomyositis

Pathophysiological Mechanisms and Treatment of Dermatomyositis and Immune Mediated Necrotizing Myopathies: A Focused Review

Idiopathic inflammatory myopathies (IIM), collectively known as myositis, are a composite group of rare autoimmune diseases affecting mostly skeletal muscle, although other organs or tissues may also be involved. The main clinical feature of myositis is subacute, progressive, symmetrical muscle weakness in the proximal arms and legs, whereas subtypes of myositis may also present with extramuscular features, such as skin involvement, arthritis or interstitial lung disease (ILD). Established subgroups of IIM include dermatomyositis (DM), immune-mediated necrotizing myopathy (IMNM), anti-synthetase syndrome (ASyS), overlap myositis (OM) and inclusion body myositis (IBM). Although these subgroups have overlapping clinical features, the widespread variation in the clinical manifestations of IIM suggests different pathophysiological mechanisms. Various components of the immune system are known to be important immunopathogenic pathways in IIM, although the exact pathophysiological mechanisms causing the muscle damage remain unknown. Current treatment, which consists of glucocorticoids and other immunosuppressive or immunomodulating agents, often fails to achieve a sustained beneficial response and is associated with various adverse effects. New therapeutic targets have been identified that may improve outcomes in patients with IIM. A better understanding of the overlapping and diverging pathophysiological mechanisms of the major subgroups of myositis is needed to optimize treatment. The aim of this review is to report on recent advancements regarding DM and IMNM.

Beyond Systemic Lupus Erythematosus and Anti-Phospholipid Syndrome: The Relevance of Complement From Pathogenesis to Pregnancy Outcome in Other Systemic Rheumatologic Diseases

Evidence about the relevance of the complement system, a highly conserved constituent of the innate immunity response that orchestrates the elimination of pathogens and the inflammatory processes, has been recently accumulated in many different rheumatologic conditions. In rheumatoid arthritis, complement, mainly the classical pathway, contributes to tissue damage especially in seropositive subjects, with complement activation occurring in the joint. Data about complement pathways in psoriatic arthritis are dated and poorly consistent; among patients with Sjögren syndrome, hypocomplementemia exerts a prognostic role, identifying patients at risk of extra-glandular manifestations. Hints about complement involvement in systemic sclerosis have been recently raised, following the evidence of complement deposition in affected skin and in renal samples from patients with scleroderma renal crisis. In vasculitides, complement plays a dual role: on one hand, stimulation of neutrophils with anti-neutrophil cytoplasmic antibodies (ANCA) results in the activation of the alternative pathway, on the other, C5a induces translocation of ANCA antigens, favouring the detrimental role of antibodies. Complement deposition in the kidneys identifies patients with more aggressive renal disease; patients with active disease display low serum levels of C3 and C4. Even though in dermatomyositis sC5b-9 deposits are invariably present in affected muscles, data on C3 and C4 fluctuation during disease course are scarce. C3 and C1q serum levels have been explored as potential markers of disease activity in Takayasu arteritis, whereas data in Behçet disease are limited to in vitro observations. Pregnancies in women with rheumatologic conditions are still burdened by a higher rate of pregnancy complications, thus the early identification of women at risk would be invaluable. A fine-tuning of complement activation is required from a physiological progression of pregnancy, from pre-implantation stages, through placentation to labour. Complement deregulation has been implicated in several pregnancy complications, such as recurrent abortion, eclampsia and premature birth; low complement levels have been shown to reliably identify women at risk of complications. Given its physiologic role in orchestrating pregnancy progression and its involvement as pathogenic effector in several rheumatologic conditions, complement system is an attractive candidate biomarker to stratify the obstetric risk among women with rheumatologic conditions.

Complement as a Therapeutic Target in Systemic Autoimmune Diseases

The complement system (CS) includes more than 50 proteins and its main function is to recognize and protect against foreign or damaged molecular components. Other homeostatic functions of CS are the elimination of apoptotic debris, neurological development, and the control of adaptive immune responses. Pathological activation plays prominent roles in the pathogenesis of most autoimmune diseases such as systemic lupus erythematosus, antiphospholipid syndrome, rheumatoid arthritis, dermatomyositis, and ANCA-associated vasculitis. In this review, we will review the main rheumatologic autoimmune processes in which complement plays a pathogenic role and its potential relevance as a therapeutic target.

Genetic Association of the Porcine C9 Complement Component with Hemolytic Complement Activity

The complement system is a part of the natural immune regulation mechanism against invading pathogens. Complement activation from three different pathways (classical, lectin, and alternative) leads to the formation of C5-convertase, an enzyme for cleavage of C5 into C5a and C5b, followed by C6, C7, C8, and C9 in membrane attack complex. The C9 is the last complement component of the terminal lytic pathway, which plays an important role in lysis of the target cells depending on its self-polymerization to form transmembrane channels. To address the association of C9 with traits related to disease resistance, the complete porcine C9 cDNA was comparatively sequenced to detect single nucleotide polymorphisms (SNPs) in pigs of the breeds Hampshire (HS), Duroc (DU), Berlin miniature pig (BMP), German Landrace (LR), Pietrain (PIE), and Muong Khuong (Vietnamese potbelly pig). Genotyping was performed in 417 F2 animals of a resource population (DUMI: DU×BMP) that were vaccinated with Mycoplasma hyopneumoniae, Aujeszky diseases virus and porcine respiratory and reproductive syndrome virus at 6, 14 and 16 weeks of age, respectively. Two SNPs were detected within the third exon. One of them has an amino acid substitution. The European porcine breeds (LR and PIE) show higher allele frequency of these SNPs than Vietnamese porcine breed (MK). Association of the substitution SNP with hemolytic complement activity indicated statistically significant differences between genotypes in the classical pathway but not in the alternative pathway. The interactions between eight time points of measurement of complement activity before and after vaccinations and genotypes were significantly different. The difference in hemolytic complement activity in the both pathways depends on genotype, kind of vaccine, age and the interaction to the other complement components. These results promote the porcine C9 (pC9) as a candidate gene to improve general animal health in the future.

Membranoproliferative pattern of glomerular injury associated with complement component 9 deficiency due to Arg95Stop mutation

BACKGROUND

Arg95Stop mutation of exon 4 in complement component 9 (C9) gene is common in individuals in Japan with C9 deficiency (C9D); however, understanding of the influences of C9D on human glomerulonephritis remains elusive.

METHODS

A total of 1288 patients with chronic kidney disease (CKD) were recruited from the hospitals in Niigata prefecture. They were screened for the Arg95Stop mutation of C9 gene by allele-specific PCR.

RESULTS

We identified two individuals with C9D among 1,288 CKD patients, a frequency comparable to that of the general Japanese population (0.16%). Case 1 involved a 44-year-old man presenting with nephrotic proteinuria. The hemolytic activity of CH50 was low, and the concentration of C9 was not detected. Sequencing of exon 4 of the C9 gene showed the Arg95Stop mutation. Renal biopsy revealed diffuse global mesangial proliferation with extensive duplication of glomerular capillary walls. Mesangial, subendothelial and subepithelial deposits were noticed with light and electron microscopy. Immunofluorescent study showed predominant mesangial IgA deposition. Case 2 involved a 62-year-old man presenting with proteinuria and hematuria. His CH50 level was decreased. Renal biopsy revealed diffuse global mesangial proliferation with extensive duplication of glomerular capillary walls. Immune deposits were also confirmed. The percentage of C9D among patients with mesangial proliferation and duplication of GBM in this study was 5.1%.

CONCLUSION

These results suggested that the lack of membrane attack complex because of an Arg95Stop mutation of the C9 gene predisposed patients to pathognomonic glomerulonephritis.

Vaccinia virus-specific molecular signature in atopic dermatitis skin

BACKGROUND

Eczema vaccinatum (EV), a disseminated viral skin infection, is a life-threatening complication of vaccinia virus (VV) inoculation in patients with atopic dermatitis (AD) and is thought to be associated with a defective innate immune response. However, the precise mechanism or mechanisms and key factor or factors of EV are unknown.

OBJECTIVE

Given that patients with psoriasis, another inflammatory skin disorder, are not susceptible to EV, we compared the global transcriptional response of skin to VV in healthy subjects, patients with psoriasis, and patients with AD, focusing on AD-specific genes. We hypothesized that differences in the transcriptional response to VV between patients with AD and patients with psoriasis or healthy subjects would identify a defective pathway or pathways that might be associated with the development of EV.

METHODS

Gene expression profiling of sham-treated and VV-treated unaffected skin explants from patients with AD (n = 12), patients with psoriasis (n = 12), or healthy subjects (n = 13) were generated with U133_Plus2 (54,613 probe sets) GeneChips and analyzed with the GCOS_1.4/SAM_2.1/MAPPFinder_2.0 pipeline.

RESULTS

Sixty-seven genes were significantly affected by VV in AD skin but not in psoriatic and healthy skin. Genes associated with defense response, response to wounding, and immune response were the most affected by VV in AD skin. All genes in these ontologies were downregulated, including the innate immunity genes leukotriene B(4) receptor (LTB4R), orosomucoid 1 (ORM1), coagulation factor II (thrombin) receptor (F2R), complement component 9 (C9), and LPS-binding protein (LBP). These findings were confirmed by means of real-time PCR and validated by means of PubMatrix analysis. ORM1, Toll-like receptor 4 (TLR4), and NLR family pyrin domain containing 1 (NLRP1) genes were also linked to AD severity.

CONCLUSION

This study identified groups of innate immunity genes that are associated with the aberrant response of AD skin to VV and represent potential targets for EV pathogenesis.

Deficiency of the human complement regulatory protein factor H associated with low levels of component C9

We identified a 4-year-old Brazilian boy from a family of Japanese descent and history of consanguinity, who suffered from severe recurrent pneumonia. He carries factor H (FH) deficiency associated with reduced levels of component C9 and low serum levels of C3 and factor B. His mother also presented low levels of these proteins and factor I, while his father and sister had only lower levels of FH. Western blot assays confirmed the complete absence of FH and FHL-1 polypeptides in this patient. Sequencing of the proband's FH cDNA revealed a homozygous G453A substitution, encoding an Arg(127)His change. His mother, father and sister are heterozygous for this substitution. Despite the absence of FH in the plasma, this protein was detected in the patient's fibroblasts, suggesting that Arg(127) may be important for FH secretion. Low concentrations of C9 were detected in the proband serum but no mutations in the patient's C9 gene or promoter have been identified, suggesting that this is a consequence of uncontrolled complement activation and high C9 consumption.

Dermatomyositis

Dermatomyositis (DM) is a chronic inflammatory disorder of the skin and muscles. Although thought to be autoimmune in origin, many questions remain as to the etiopathogenesis of this disease. DM has classically been considered a humorally mediated disease. Current evidence, however, seems to increasingly support alternative (though not mutually exclusive) mechanisms of pathogenesis, including cell-mediated and innate immune system dysfunction. Pathologic findings of DM in muscle include infarcts, perifascicular atrophy, endothelial cell swelling and necrosis, vessel wall membrane attack complex deposition, and myocyte-specific MHC I upregulation. As for the skin, histopathologic findings include hyperkeratosis, epidermal basal cell vacuolar degeneration and apoptosis, increased dermal mucin deposition, and a cell-poor interface dermatitis. Autoantibodies, particularly those that bind nuclear or cytoplasmic ribonucleoprotein antigens, are also commonly found in DM, although their importance in pathogenesis remains unclear. Defective cellular clearance, genetic predilection and environmental exposures, such as viral infection, may also play an important role in the pathogenesis of DM. The seminal work regarding the pathogenesis of DM is reviewed and an update on the recent basic and molecular advances in the field is provided.

A systematic review of adult-onset clinically amyopathic dermatomyositis (dermatomyositis siné myositis): a missing link within the spectrum of the idiopathic inflammatory myopathies

OBJECTIVE

Classical dermatomyositis (CDM) patients display the hallmark cutaneous manifestations of dermatomyositis (DM), proximal muscle weakness, and laboratory evidence of myositis. The epidemiology and management of both adult-onset and juvenile-onset CDM has been well characterized. However, the clinical significance of the hallmark inflammatory cutaneous manifestations of DM occurring in individuals who have no clinically significant muscle weakness and normal muscle enzymes for prolonged periods of time (ie, 6 months or longer) has not been clear. The term amyopathic DM (ADM) (synonymous with DM siné myositis) has been proposed to draw attention to such individuals. A related form of DM, "hypomyopathic DM" [HDM], is the presence of DM skin disease for 6 months or longer in individuals who have no muscle weakness but who are found to have some evidence of muscle inflammation upon testing (muscle enzyme levels, electromyogram, muscle biopsy, muscle magnetic resonance imaging [MRI]). Clinically amyopathic DM (CADM) is a designation that has been proposed for patients having either ADM or HDM. The clinically amyopathic component of this designation was coined to emphasize the fact that the only clinical problem being experienced by these patients at the time of diagnosis is their DM skin disease. Our personal experience suggests that the CADM subphenotype might be more prevalent in adults than has been thought previously. To test this hypothesis and address questions relating to the optimal management and prognosis of such patients, we have systematically reviewed the published literature in this area.

METHODS

We carried out a systematic review of the published literature on adult-onset CADM as defined in Table 1 through May 1, 2004.

RESULTS

We identified 291 adult-onset CADM cases (18 years or older) reported from over 19 countries. The average duration of DM skin disease was 3.74 years (range, 6 months [by definition] to > 20 years), and 73% were female. Among 37 patients with HDM who were identified, the average duration of disease was 5.4 years, and none had developed clinically significant weakness at the time of the reports. Thirty-seven of the reported CADM patients developed muscle weakness greater than 6 months after onset of their skin disease (15 months to 6 years). For the sake of this discussion, such patients have been analyzed under the designation of "CADM --> CDM." Somewhat surprisingly, 36/291 (13%) of the identified published CADM patients developed interstitial lung disease. Incidental to our review, we also identified 10 published cases of individuals having DM skin disease and interstitial lung disease without muscle weakness, 7 of whom died from interstitial lung disease less than 6 months after onset of their DM skin disease (the term pre-myopathic DM coined by others has been used here to refer to such patients). In addition, an associated internal malignancy was found in 41/291 (14%) of the identified CADM cases. A positive antinuclear antibody was reported in 63% and myositis-specific autoantibodies (eg, Jo-1, Mi-2) in only 3.5% of the reported CADM patients in which such data were available.

CONCLUSIONS

The results of this analysis suggests that the CADM subphenotype is more common than has been thought previously and that such patients may comprise a relatively high proportion of DM patients followed by dermatologists. Some CADM patients also have been observed to develop overt proximal muscle weakness years after onset of their DM skin disease. In addition, CADM patients appear to be at risk of developing the same potentially fatal disease associations/complications for which CDM patients are at risk (eg, interstitial lung disease and internal malignancy). Population-based studies of the epidemiology and optimal management of CADM patients, including efforts to identify risk factors associated with potentially fatal outcomes such as late-onset muscle weakness, interstitial lung disease, and malignancy, are needed. As an incidental finding to this literature review, we also identified a small number of reported cases of often-fatal interstitial lung disease occurring shortly after the onset of DM skin disease (< 6 months) in the complete absence of muscle weakness. This subphenotype, referred to as "pre-myopathic DM," is one with which dermatologists should be aware as early diagnosis and aggressive management can be lifesaving.

Uncertainties in the pathogenesis of adult dermatomyositis

PURPOSE OF REVIEW

Dermatomyositis is an inflammatory disorder of muscle affecting both children and adults. The pathogenesis of adult dermatomyositis is reviewed here, with particular attention to gaps and uncertainties in our current understanding of this disease, in order to focus attention on the outstanding research questions with regard to disease mechanisms.

RECENT FINDINGS

The conceptual model of the pathophysiology of dermatomyositis has been based on work extending back over at least 35 years, with important findings related to the deposition of membrane attack complex, the character of the inflammatory infiltrate, and the primacy of capillary abnormalities established over 10 years ago. The lack of significant additions to the understanding of this disease over the past few years suggests a state of contentment with current knowledge. Accordingly, we emphasize the uncertainties of this knowledge and the need for re-addressing some of its basic tenets.

SUMMARY

Although evidence remains strong that dermatomyositis is a disorder with an early involvement of the capillaries, the concept that it results from an antibody-mediated attack upon the endothelium is uncertain. It is not clear whether membrane attack complex is activated by antibody-dependent or independent means, whether or not intramuscular B cells are antigen specific and synthesize significant quantities of antibodies, whether the presence of tubuloreticular inclusions precedes, follows, or is independent of membrane attack complex deposition, what is the mechanism of perifascicular atrophy, and what is the relationship of dermatomyositis to systemic lupus erythematosus.

Juvenile dermatomyositis: immunogenetics, pathophysiology, and disease expression

Data are rapidly accumulating documenting disease susceptibility may be linked to genetic markers (DQA1*0501 or related alleles) which are associated with upregulation of IFN-alpha/beta inducible genes elicited in response to an antigen which may be viral. Continued immune-mediated inflammation, resulting in partial lipodystrophy and pathological calcifications, may be fanned by the increased production of TNF alpha usually associated with the TNF alpha-308A allele.

Dermatomyositis: an overview of recent progress with emphasis on dermatologic aspects

Important points regarding DM and C-ADM are as follows: C-ADM is a working functional designation for patients having the skin-only and skin-predominant subsets of DM, amyopathic DM, and hypomyopathic DM. C-ADM seems to have approximately 10% the incidence of classic DM in whites and possibly a higher incidence in Asians. Some patients who present with C-ADM, with or without subclinical laboratory abnormalities, can slowly progress to develop symptomatic muscle weakness over a period of years, whereas others go for 10 to 20 years and longer without the appearance of muscle weakness. C-ADM patients are at risk for potentially life-threatening complications of classic DM, such as interstitial lung disease, which may occur in up to 10% of C-ADM patients. This risk seems to be even greater in some ethnic subgroups (e.g., Japanese). C-ADM patients may also be at increased risk for internal malignancy and until further studies are carried out to confirm the statistical significance of this association, all such patients should have a thorough evaluation for internal malignancy, identical to the approach currently used in classic DM patients. Dermatologists are in the best position initially to diagnose C-ADM patients and can contribute greatly to their overall management and quality of life. Ongoing vigilance is required, however, for complications that can arise in C-ADM patients including potentially fatal interstitial lung disease, internal malignancy, delayed onset of muscle weakness from myositis, and complications of systemic drug therapy. Topical therapy with broad-spectrum sunscreens, anti-inflammatories, and antipruritics should be maximized during the initial management of the cutaneous manifestations of either classic DM or C-ADM. Single-agent or combined aminoquinoline antimalarial therapy represents the safest initial form of systemic therapy for DM-specific skin disease occurring in any clinical setting; however, this approach tends to be less effective in general than for cutaneous LE. There is a theoretical rationale for and limited preliminary successful anecdotal experience with the use of anti-TNF-alpha therapy in refractory cases of classic DM and C-ADM. Cautious systematic clinical trials in this area should be considered.