Type I human complement C2 deficiency. A 28-base pair gene deletion causes skipping of exon 6 during RNA splicing

Clinical exome analysis and targeted gene repair of the c.1354dupT variant in iPSC lines from patients with PROM1-related retinopathies exhibiting diverse phenotypes

BACKGROUND

Inherited retinal dystrophies (IRD) are one of the main causes of incurable blindness worldwide. IRD are caused by mutations in genes that encode essential proteins for the retina, leading to photoreceptor degeneration and loss of visual function. IRD generates an enormous global financial burden due to the lack of understanding of a significant part of its pathophysiology, molecular diagnosis, and the near absence of non-palliative treatment options. Patient-derived induced pluripotent stem cells (iPSC) for IRD seem to be an excellent option for addressing these questions, serving as exceptional tools for in-depth studies of IRD pathophysiology and testing new therapeutic approaches.

METHODS

From a cohort of 8 patients with PROM1-related IRD, we identified 3 patients carrying the same variant (c.1354dupT) but expressing three different IRD phenotypes: Cone and rod dystrophy (CORD), Retinitis pigmentosa (RP), and Stargardt disease type 4 (STGD4). These three target patients, along with one healthy relative from each, underwent comprehensive ophthalmic examinations and their genetic panel study was expanded through clinical exome sequencing (CES). Subsequently, non-integrative patient-derived iPSC were generated and fully characterized. Correction of the c.1354dupT mutation was performed using CRISPR/Cas9, and the genetic restoration of the PROM1 gene was confirmed through flow cytometry and western blotting in the patient-derived iPSC lines.

RESULTS

CES revealed that 2 target patients with the c.1354dupT mutation presented monoallelic variants in genes associated with the complement system or photoreceptor differentiation and peroxisome biogenesis disorders, respectively. The pluripotency and functionality of the patient-derived iPSC lines were confirmed, and the correction of the target mutation fully restored the capability of encoding Prominin-1 (CD133) in the genetically repaired patient-derived iPSC lines.

CONCLUSIONS

The c.1354dupT mutation in the PROM1 gene is associated to three distinct AR phenotypes of IRD. This pleotropic effect might be related to the influence of monoallelic variants in other genes associated with retinal dystrophies. However, further evidence needs to be provided. Future experiments should include gene-edited patient-derived iPSC due to its potential as disease modelling tools to elucidate this matter in question.

The complement system and human autoimmune diseases

Genetic deficiencies of early components of the classical complement activation pathway (especially C1q, r, s, and C4) are the strongest monogenic causal factors for the prototypic autoimmune disease systemic lupus erythematosus (SLE), but their prevalence is extremely rare. In contrast, isotype genetic deficiency of C4A and acquired deficiency of C1q by autoantibodies are frequent among patients with SLE. Here we review the genetic basis of complement deficiencies in autoimmune disease, discuss the complex genetic diversity seen in complement C4 and its association with autoimmune disease, provide guidance as to when clinicians should suspect and test for complement deficiencies, and outline the current understanding of the mechanisms relating complement deficiencies to autoimmunity. We focus primarily on SLE, as the role of complement in SLE is well-established, but will also discuss other informative diseases such as inflammatory arthritis and myositis.

Polygenic Risk Score Impact on Susceptibility to Age-Related Macular Degeneration in Polish Patients

Age-related macular degeneration (AMD) is a common retina degenerative disease with a complex genetic and environmental background. This study aimed to determine the polygenic risk score (PRS) stratification between the AMD case and control patients. The PRS model was established on the targeted sequencing data of a cohort of 471 patients diagnosed with AMD and 167 healthy controls without symptoms of retinal degeneration. The highest predictive value to the target dataset was achieved for a 22-variant model with a p-value lower than threshold PT = 0.0123. The median PRS for cases was higher by 1.1 than for control samples (95% CI: (−1.19; −0.85)). The patients in the highest quantile had a significantly higher relative risk of developing AMD than those in the lowest reference quantile (OR = 35.13, 95% CI: (7.9; 156.1), p < 0.001). The diagnostic ability was investigated using ROC analysis with AUC = 0.76 (95% CI: (0.72; 0.80)). The polygenic susceptibility to AMD may be the starting point to expand AMD diagnostics based on rare highly penetrant variants and investigate associations with disease progression and treatment response in Polish patients in future studies.

Strong Association of Combined Genetic Deficiencies in the Classical Complement Pathway With Risk of Systemic Lupus Erythematosus and Primary Sjögren's Syndrome

OBJECTIVE

Complete genetic deficiency of the complement component C2 is a strong risk factor for monogenic systemic lupus erythematosus (SLE), but whether heterozygous C2 deficiency adds to the risk of SLE or primary Sjögren's syndrome (SS) has not been studied systematically. This study was undertaken to investigate potential associations of heterozygous C2 deficiency and C4 copy number variation with clinical manifestations in patients with SLE and patients with primary SS.

METHODS

The presence of the common 28-bp C2 deletion rs9332736 and C4 copy number variation was examined in Scandinavian patients who had received a diagnosis of SLE (n = 958) or primary SS (n = 911) and in 2,262 healthy controls through the use of DNA sequencing. The concentration of complement proteins in plasma and classical complement function were analyzed in a subgroup of SLE patients.

RESULTS

Heterozygous C2 deficiency-when present in combination with a low C4A copy number-substantially increased the risk of SLE (odds ratio [OR] 10.2 [95% confidence interval (95% CI) 3.5-37.0]) and the risk of primary SS (OR 13.0 [95% CI 4.5-48.4]) when compared to individuals with 2 C4A copies and normal C2. For patients heterozygous for rs9332736 with 1 C4A copy, the median age at diagnosis was 7 years earlier in patients with SLE and 12 years earlier in patients with primary SS when compared to patients with normal C2. Reduced C2 levels in plasma (P = 2 × 10-9 ) and impaired function of the classical complement pathway (P = 0.03) were detected in SLE patients with heterozygous C2 deficiency. Finally, in a primary SS patient homozygous for C2 deficiency, we observed low levels of anti-Scl-70, which suggests a risk of developing systemic sclerosis or potential overlap between primary SS and other systemic autoimmune diseases.

CONCLUSION

We demonstrate that a genetic pattern involving partial deficiencies of C2 and C4A in the classical complement pathway is a strong risk factor for SLE and for primary SS. Our results emphasize the central role of the complement system in the pathogenesis of both SLE and primary SS.

Complement Genetics for the Practicing Allergist Immunologist: Focus on Complement Deficiencies

Complement deficiencies have been considered to be rare for many decades, but this assumption is changing year by year. Recognition of these conditions significantly increases thanks to the availability of different testing approaches and due to clinical awareness. Furthermore, sequencing technologies (including Sanger sequencing, targeted gene panels, and whole exome/genome sequencing) may facilitate the identification of the underlying disease-causing genetic background. On the other hand, functional characterization of the identified possibly pathogenic variations and performing family studies, as illustrated by some of our cases, remain similarly important to establish a precise clinical diagnosis facilitating the most appropriate management. Here, we present 4 illustrative cases with complement deficiencies of diverse etiologies and also provide an educative, step-by-step description on how to identify the underlying cause of complement deficiency based on the results of complement laboratory testing.

Lessons of the month 2: Meningococcal epiglottitis and connective tissue disease associated with C2 deficiency

CASE PRESENTATION

A 68-year-old woman was referred for immunological investigation following an episode of meningococcal epiglottitis with associated septicaemia. Several years previously, she had been diagnosed with undifferentiated connective tissue disease. On investigation, alternative pathway complement function was normal; however, classical pathway complement activation was reduced. C1q, C3 and C4 levels were all measured and found to be within their respective normal ranges, but C2 levels were low. Sequencing of the C2 gene was subsequently performed, confirming a diagnosis of type 1 C2 deficiency (C2D).

DISCUSSION

C2D is usually hereditary and inherited in an autosomal recessive manner. C2D is often asymptomatic, however, some patients suffer from infections with encapsulated bacteria and/or autoimmune diseases, particularly systemic lupus erythematosus. Recognition of complement pathway deficiency is important due to the predisposition to severe and/or recurrent infections by encapsulated bacteria. Immunisations have the potential to reduce both mortality and morbidity not only for the patient but also for any affected relatives.

Increased serum bactericidal activity of autologous serum in C2 deficiency after vaccination against Haemophilus influenzae type b, and further support for an MBL-dependent C2 bypass mechanism

Deficiencies of C2 and other components of the classical pathway of complement are associated with increased risk of infections with encapsulated bacteria, such as Haemophilus (H.) influenzae. Defense against H. influenzae is dependent on specific antibodies and complement, which mediate serum bactericidal activity (SBA) and opsonization. Due to lack of normal classical and lectin complement pathway function in C2 deficiency (C2D), SBA would have to depend either on the alternative pathway or on C2 bypass mechanisms. Here we studied SBA against H. influenzae type b (Hib) before and after vaccination in a group of C2-deficient persons, as the bactericidal capacity of antibodies in autologous complement in relation to vaccination has not been investigated at group level in C2D. Sera from 22 persons with C2D and 26 healthy controls were available. Out of these, 18 persons with C2D and all controls had been vaccinated with Act-HIB®. SBA against Hib bacteria was analyzed with autologous serum as the only complement source. Antibodies to Hib capsular polysaccharide had been analyzed previously. Concentrations of mannose-binding lectin (MBL) and other complement components were measured in serum. SBA of both C2-deficient persons and controls was significantly more efficient after vaccination (p = 0.002 and p < 0.0001, respectively). After vaccination, all but two C2-deficient sera and one control serum showed sufficient SBA (<50% surviving bacteria). Before vaccination, SBA of C2-deficient sera was negatively correlated to serum concentrations of MBL (lower proportion of surviving bacteria with higher MBL concentration; r = -0.55, p = 0.008). After vaccination, SBA of C2-deficient sera was negatively correlated to serum concentrations of IgG Hib antibodies (r = -0.56, p = 0.01). In conclusion, SBA against Hib in autologous serum is increased after vaccination in persons with C2D. In unvaccinated C2-deficient persons SBA was correlated to MBL concentration, providing further support for an MBL-dependent C2 bypass mechanism operating in C2D.

Clinical and Genetic Spectrum of a Large Cohort With Total and Sub-total Complement Deficiencies

The complement system is crucial for defense against pathogens and the removal of dying cells or immune complexes. Thus, clinical indications for possible complete complement deficiencies include, among others, recurrent mild or serious bacterial infections as well as autoimmune diseases (AID). The diagnostic approach includes functional activity measurements of the classical (CH50) and alternative pathway (AP50) and the determination of the C3 and C4 levels, followed by the quantitative analysis of individual components or regulators. When biochemical analysis reveals the causal abnormality of the complement deficiency (CD), molecular mechanisms remains frequently undetermined. Here, using direct sequencing analysis of the coding region we report the pathogenic variants spectrum that underlie the total or subtotal complement deficiency in 212 patients. We identified 107 different hemizygous, homozygous, or compound heterozygous pathogenic variants in 14 complement genes [C1Qβ (n = 1), C1r (n = 3), C1s (n = 2), C2 (n = 12), C3 (n = 5), C5 (n = 12), C6 (n = 9), C7 (n = 17), C8 β (n = 7), C9 (n = 3), CFH (n = 7), CFI (n = 18), CFP (n = 10), CFD (n = 2)]. Molecular analysis identified 17 recurrent pathogenic variants in 6 genes (C2, CFH, C5, C6, C7, and C8). More than half of the pathogenic variants identified in unrelated patients were also found in healthy controls from the same geographic area. Our study confirms the strong association of meningococcal infections with terminal pathway deficiency and highlights the risk of pneumococcal and auto-immune diseases in the classical and alternative pathways. Results from this large genetic investigation provide evidence of a restricted number of molecular mechanisms leading to complement deficiency and describe the clinical potential adverse events of anti-complement therapy.

Quantification of human complement C2 protein using an automated turbidimetric immunoassay

BACKGROUND

The measurement of complement components is clinically useful where a deficiency is suspected, or where excessive activation and consumption are present in disease. C2 deficiency carries an increased risk of developing systemic lupus erythematosus, recurrent infections and atherosclerosis. In this study, we have evaluated The Binding Site's Human Complement C2 SPAPLUS® assay.

METHODS

Linearity was tested using 13 sample dilutions covering the standard measuring range. Within- and between-assay variabilities were calculated using five samples with different C2 concentrations. The correlation between C2 concentrations in EDTA-plasma and serum was assessed, as was the correlation between C2 measurements by the automated assay and radial immunodiffusion. C2 concentrations were compared with CH50 activity, and quantified in individuals with homozygous or heterozygous C2 deficiency, acquired angioedema and patients with chronic inflammatory conditions.

RESULTS

The assay was linear across the measuring range (3.8-42.3 mg/L). Intra- and interassay variability were 2.3%-3.8% and 0%-3.3%, respectively. Comparison between C2 measurements in EDTA-plasma and serum provided a strong correlation (p<0.0001, R2=0.82, slope 0.92), as did the correlation between the automated and radial immunodiffusion methods (p<0.0001, R2=0.89, slope 1.07). A positive correlation between C2 concentration and CH50 activity was demonstrated (p<0.0001, R2=0.48). Significant differences were observed between the median C2 concentrations obtained in healthy controls and the patient clinical samples, with homozygous C2-deficient patients giving below detectable results.

CONCLUSIONS

This C2 SPAPLUS® assay allows the automated, rapid and precice quantification of complement C2 protein and could therefore be considered as a replacement for older, more time-consuming methods.

Complement in autoimmune diseases

The complement system is an ancient and evolutionary conserved element of the innate immune mechanism. It comprises of more than 20 serum proteins most of which are synthesized in the liver. These proteins are synthesized as inactive precursor proteins which are activated by appropriate stimuli. The activated forms of these proteins act as proteases and cleave other components successively in amplification pathways leading to exponential generation of final effectors. Three major pathways of complement pathways have been described, namely the classical, alternative and lectin pathways which are activated by different stimuli. However, all the 3 pathways converge on Complement C3. Cleavage of C3 and C5 successively leads to the production of the membrane attack complex which is final common effector. Excessive and uncontrolled activation of the complement has been implicated in the host of autoimmune diseases. But the complement has also been bemusedly described as the proverbial "double edged sword". On one hand, complement is the final effector of tissue injury in autoimmune diseases and on the other, deficiencies of some components of the complement can result in autoimmune diseases. Currently available tools such as enzyme based immunoassays for functional assessment of complement pathways, flow cytometry, next generation sequencing and proteomics-based approaches provide an exciting opportunity to study this ancient yet mysterious element of innate immunity.

Early Components of the Complement Classical Activation Pathway in Human Systemic Autoimmune Diseases

The complement system consists of effector proteins, regulators, and receptors that participate in host defense against pathogens. Activation of the complement system, via the classical pathway (CP), has long been recognized in immune complex-mediated tissue injury, most notably systemic lupus erythematosus (SLE). Paradoxically, a complete deficiency of an early component of the CP, as evidenced by homozygous genetic deficiencies reported in human, are strongly associated with the risk of developing SLE or a lupus-like disease. Similarly, isotype deficiency attributable to a gene copy-number (GCN) variation and/or the presence of autoantibodies directed against a CP component or a regulatory protein that result in an acquired deficiency are relatively common in SLE patients. Applying accurate assay methodologies with rigorous data validations, low GCNs of total C4, and heterozygous and homozygous deficiencies of C4A have been shown as medium to large effect size risk factors, while high copy numbers of total C4 or C4A as prevalent protective factors, of European and East-Asian SLE. Here, we summarize the current knowledge related to genetic deficiency and insufficiency, and acquired protein deficiencies for C1q, C1r, C1s, C4A/C4B, and C2 in disease pathogenesis and prognosis of SLE, and, briefly, for other systemic autoimmune diseases. As the complement system is increasingly found to be associated with autoimmune diseases and immune-mediated diseases, it has become an attractive therapeutic target. We highlight the recent developments and offer a balanced perspective concerning future investigations and therapeutic applications with a focus on early components of the CP in human systemic autoimmune diseases.

Overview of Laboratory Testing and Clinical Presentations of Complement Deficiencies and Dysregulation

Historically, complement disorders have been attributed to immunodeficiency associated with severe or frequent infection. More recently, however, complement has been recognized for its role in inflammation, autoimmune disorders, and vision loss. This paradigm shift requires a fundamental change in how complement testing is performed and interpreted. Here, we provide an overview of the complement pathways and summarize recent literature related to hereditary and acquired angioedema, infectious diseases, autoimmunity, and age-related macular degeneration. The impact of complement dysregulation in atypical hemolytic uremic syndrome, paroxysmal nocturnal hemoglobinuria, and C3 glomerulopathies is also described. The advent of therapeutics such as eculizumab and other complement inhibitors has driven the need to more fully understand complement to facilitate diagnosis and monitoring. In this report, we review analytical methods and discuss challenges for the clinical laboratory in measuring this complex biochemical system.

Primary complement and antibody deficiencies in autoimmune rheumatologic diseases with juvenile onset: a prospective study at two centers

BACKGROUND

Our aim was to investigate the prevalence and clinical relevance of inherited complement and antibody deficiency states in a large series of patients with various autoimmune rheumatologic diseases (ARD) with juvenile onset.

METHODS

A total number of 117 consecutive patients from 2 tertiary referral hospitals were included in the study. All patients underwent genetic screening for type I C2 deficiency and C4 allotyping. Serum levels of immunoglobulin classes measured systematically throughout their regular medical care were recorded retrospectively.

RESULTS

Our cohort of patients included 84 with juvenile idiopathic arthritis (JIA), 21 with systemic lupus erythematosus (SLE), 6 with systemic vasculitis, 2 with juvenile scleroderma, 2 with idiopathic uveitis, 1 with mixed connective tissue disease and 1 with SLE/scleroderma overlap syndrome. We have found 16 patients with evidence of primary immunodeficiency in our series (13.7%), including 7 with C4 deficiency, 5 with selective IgA deficiency, 3 with C2 deficiency and 2 with unclassified hypogammaglobulinemia (one also presented C4D). Of the 84 patients with JIA, 4 (4.8%) had a complement deficiency, which was less prevalent than in the SLE cohort (23.8%), but all of them have exhibited an aggressive disease. Most of our patients with primary antibody deficiencies showed a more complicated and severe disease course and even the co-occurrence of two associated autoimmune diseases (SLE/scleroderma overlap syndrome and SLE/autoimmune hepatitis type 1 overlap).

CONCLUSIONS

Our findings among others demonstrate that complement and immunoglobulin immunodeficiencies need careful consideration in patients with ARD, as they are common and might contribute to a more severe clinical course of the disease.

Immunodeficiency among children with recurrent invasive pneumococcal disease

BACKGROUND

Recurrent invasive pneumococcal disease (rIPD) occurs mostly in children with an underlying disease, but some cases remain unexplained. Immunodeficiency has been described in children with rIPD, but the prevalence is unknown. We used a nationwide registry of all laboratory-confirmed cases of rIPD to identify cases of unexplained rIPD and examine them for immunodeficiency.

METHODS

Cases of rIPD in children 0-15 years of age from 1980 to 2008 were identified. Children without an obvious underlying disease were screened for complement function, T-cell, B-cell, natural killer--cell counts and concentration of immunoglobulins. B-cell function was evaluated by measuring antibody response to polysaccharide-based pneumococcal vaccination and the extent of fraction of somatic hypermutation. Toll-Like receptor (TLR) signaling function and mutations in key TLR-signaling molecules were examined.

RESULTS

In total, rIPD were observed in 54 children (68 cases of rIPD of 2192 IPD cases). Children with classical risk factors for IPD were excluded, and among the remaining 22 children, 15 were eligible for analysis. Of these 6 (40%) were complement C2-deficient. Impaired vaccination response was found in 6 children of whom 3 were C2 deficient. One patient had a severe TLR signaling dysfunction. No mutations in IRAK4, IKBKG or MYD88 were found.

CONCLUSION

Of an unselected cohort of children with rIPD at least 11% were C2 deficient. Data suggest that screening for complement deficiencies and deficient antibody response to pneumococcal vaccines in patients with more than 1 episode of IPD is warranted.

Molecular characterization of the complement C1q, C2 and C4 genes in Brazilian patients with juvenile systemic lupus erythematosus

OBJECTIVE

To perform a molecular characterization of the C1q, C2 and C4 genes in patients with juvenile systemic lupus erythematosus.

METHODS

Patient 1 (P1) had undetectable C1q, patient 2 (P2) and patient 3 (P3) had decreased C2 and patient 4 (P4) had decreased C4 levels. All exons and non-coding regions of the C1q and C2 genes were sequenced. Mononuclear cells were cultured and stimulated with interferon gamma to evaluate C1q, C2 and C4 mRNA expression by quantitative real-time polymerase chain reaction.

RESULTS

C1q sequencing revealed heterozygous silent mutations in the A (c.276 A>G Gly) and C (c.126 C>T Pro) chains, as well as a homozygous single-base change in the 3' non-coding region of the B chain (c*78 A>G). C1qA mRNA expression without interferon was decreased compared with that of healthy controls (p<0.05) and was decreased after stimulation compared with that of non-treated cells. C1qB mRNA expression was decreased compared with that of controls and did not change with stimulation. C1qC mRNA expression was increased compared with that of controls and was even higher after stimulation. P2 and P3 had Type I C2 deficiency (heterozygous 28 bp deletion at exon 6). The C2 mRNA expression in P3 was 23 times lower compared with that of controls and did not change after stimulation. The C4B mRNA expression of P4 was decreased compared with that of controls and increased after stimulation.

CONCLUSIONS

Silent mutations and single-base changes in the 3' non-coding regions may modify mRNA transcription and C1q production. Type I C2 deficiency should be evaluated in JSLE patients with decreased C2 serum levels. Further studies are needed to clarify the role of decreased C4B mRNA expression in JSLE pathogenesis.

Immune responses following meningococcal serogroups A, C, Y and W polysaccharide vaccination in C2-deficient persons: evidence for increased levels of serum bactericidal antibodies

Complement C2 deficiency (C2D) is associated with immunological diseases and increased susceptibility to invasive infections caused by encapsulated bacteria such as Neisseria menigitidis. In this study we evaluate the immunogenicity of vaccination against N. menigitidis in C2D. C2D patients (n=22) and controls (n=52) were given a tetravalent meningococcal polysaccharide vaccine. Serum bactericidal antibody (SBA) titres (serogroups A, C, Y and W) were analysed using a rabbit complement source. Levels of IgG, IgM, and IgA, factor B, and factor H, polymorphisms of MBL and Fc-gamma receptors were determined. The C2D patients responded with an increased SBA titre to all four serogroups (p<0.001). The response rates define as SBA titres ≥8 were found to be between 85.7% and 92.5%. The post-vaccination titres for serogroups C, Y and W were equal to healthy controls. C2D patients with a history of invasive infection had a lower post-vaccination SBA titres both compared to healthy C2D persons (p=0.03) and compared to controls (p<0.0001). We found that the G2M*n/G2M*n genotype were associated with a higher SBA titres after immunization (p=0.03). None of the other investigated immunological factors appear to be important in influencing the vaccine responses. Autoimmune diseases in C2D did not affect the vaccine response. In general, vaccination against meningococci gave rise to antibody responses in the C2D patients that equal healthy controls. The response rate was lower to serogroup A and among C2D patients with history of invasive infections. The presence of G2M*n/G2M*n genotype was associated with higher SBA titres after immunization.

Genetic polymorphisms of innate and adaptive immunity as predictors of outcome in critically ill patients

Sepsis and septic shock frequently cause the admission or complicate the clinical course of critically ill patients admitted in the intensive care units (ICU). Genetic variations disrupting the immune sensing of infectious organisms, could affect the ability of the immune system to respond to infection, and may influence both the genetic predisposition to infection and the diversity of the clinical presentation of sepsis. The aim of this study was to uncover possible associations between common functional immune gene polymorphisms (of both innate and adaptive immunity) and ICU-acquired sepsis and mortality. The TLR4-D299G (rs4986790), TLR4-T399I (rs4986791), C2-c.841_849+19del28 (rs9332736), TACI-C104R (rs34557412), BAFFR-P21R (rs77874543), and BAFFR-H159Y (rs61756766) polymorphisms were detected in a cohort of 215 critically ill patients, admitted in an 8-bed medical/surgical ICU. Interestingly, TLR4-D299G, TLR4-T399I and BAFFR-P21R carriage was associated with a lower risk of ICU-acquired sepsis. This association applied particularly in medical patients, while in trauma and surgical patients no significant associations were observed. Moreover, carriers of TACI-C104R displayed an undiagnosed mild to moderate hypogammaglobulinemia along with a significantly lower survival rate in the ICU, although lethal events were not attributed to sepsis. These findings further elucidate the role that host immune genetic variations may play in the susceptibility to ICU-acquired sepsis and ICU mortality.

Signalling or binding: the role of the platelet-activating factor receptor in invasive pneumococcal disease

Streptococcus pneumoniae (the pneumococcus) is an opportunistic human pathogen, which causes serious invasive disease such as pneumonia, bacteraemia and meningitis. The interaction of the bacteria with host receptors precedes the development of invasive disease. One host receptor implicated in pneumococcal adhesion to, invasion of and ultimately translocation of cell layers is the platelet-activating factor receptor (PAFR). PAFR is a G-protein coupled receptor which binds PAF, a potent phospholipid activator involved in many leucocyte functions, platelet aggregation and inflammation. PAFR has been proposed to bind S. pneumoniae and as such facilitate adhesion to, uptake by and transcytosis of endothelial cells leading to invasive disease. However, there is a shortage of biochemical data supporting direct interaction between PAFR and the bacteria, in addition to conflicting data on its role in development of invasive pneumococcal disease (IPD). In this review, we will discuss current literature on PAFR and S. pneumoniae and other pathogens,including data concerning human PAFR genetic variation related to IPD clinical aspects, to shed light on the importance of PAFR in IPD. Clarification of the role of this receptor in IPD development has the potential to enable the development of novel therapeutic strategies for treating pneumococcal disease by interfering with the PAFR.

Complement and antibody primary immunodeficiency in juvenile systemic lupus erythematosus patients

OBJECTIVE

To evaluate the frequency of primary immunodeficiencies (PID) in juvenile systemic lupus erythematosus (JSLE) patients.

METHODS

Some 72 JSLE patients were analyzed for levels of immunoglobulin classes and IgG subclasses and early components of the classical complement pathway. Determination of C4 gene copy number (GCN) and detection of type I C2 deficiency (D) were also performed.

RESULTS

PID was identified in 16 patients (22%): C2D in three, C4D in three, C1qD in two, IgG2D (<20 mg/dl) in four, IgAD (<7 mg/dl) in three, and IgMD (<35 mg/dl) in three; one of these patients presented IgA, C2 and C4D. Two patients had low C4 GCN and two had type I C2D. Demographic data, family history of autoimmune disease and PID, JSLE clinical findings, occurrence of infections, disease activity and therapies were similar in patients with and without PID (p > 0.05). Remarkably, the median of Systemic Lupus International Collaborating Clinics/ACR-damage index (SLICC/ACR-DI) was significantly higher in JSLE patients with PID compared with patients without these abnormalities (p = 0.0033), likewise the high frequency of SLICC/ACR-DI > 1 (p = 0.023).

CONCLUSIONS

A high frequency of PID was observed in JSLE patients, suggesting that these defects may contribute to lupus development. Our findings indicate that these two groups of PID should be investigated in severe pediatric lupus.

Major histocompatibility complex class III (C2, C4, factor B) and C3 gene variants in patients with pulmonary tuberculosis

The complement system is an integral part of the host immune system and plays an immunoregulatory role at the interface of innate and acquired immune responses. Limited data are available on the influence of variations in complement genes in infectious diseases such as pulmonary tuberculosis (PTB). The aim of this study was to investigate the role of genetic variations in complement system components C2, C4, BF, and C3 in PTB (n = 125) compared with healthy controls (n = 125) in the Indian population. The study showed, for the first time, an increased occurrence of null alleles at the C4A, i.e., C4AQ0; an increased frequency of BF*FA and C3*F in patients with PTB compared with healthy individuals, and contributed a risk with odds ratios of 18.16 (95% confidence interval [CI] = 3.0-108.6, p = 0.0004), 2.9 (95% CI = 1.9-4.37, p(c) = 3.15E-06), and 2.26 (95% CI = 1.5-3.3, p(c) = 6.7E-05), respectively. A combinatorial analysis of complement gene variants as risk determinants and their phenotypic effects in various populations may provide unique insights into the genetic basis of susceptibility to PTB.

Cutaneous manifestations of complement deficiencies

In this review we address the main cutaneous manifestations and diseases associated with deficiencies in components of the complement system. The first part is devoted to hereditary angioedema, in which acute, sometimes life-threatening recurrent attacks of acute swelling, usually associated with gastrointestinal symptoms, occur. It is related to a structural or functional deficiency of C1 esterase inhibitor. Patients usually have lowered C4 levels, and diagnosis relies on determination of antigenic and/or functional C1 inhibitor level. The second part focuses on lupus erythematosus, as deficiencies in early components of the complement system, such as C1q, C1r, C1s, C2 or C4, are the strongest known disease susceptibility genes for the development of human systemic lupus erythematosus. Severe infections early in life and marked photosensitivity in a patient with lupus erythematosus are clues to an underlying complement deficiency. The genetic background and the clinical associations of the different components of the complement system will be detailed. Lupus (2010) 19, 1096—1106.

Complement deficiency and systemic lupus erythematosus: consensus and dilemma

The involvement of the complement system in the pathogenesis of autoimmune diseases is a matter of debate. However, the link between complement abnormalities and systemic lupus erythematosus (SLE) is well established and widely described. Homozygous and/or heterozygous complement-component deficiencies of the classical pathway (C1q, C1r, C1s, C4A, C4B and C2) are causally associated with susceptibility to the development of SLE. Although the severity of the disease and the strength of the association are heterogeneous for deficiencies of these proteins, they commonly cause peculiar SLE syndromes with an early age of onset, a susceptibility to bacterial infections and negative anti-dsDNA antibodies. In this review, we highlight the available data on complement deficiency and SLE with a focus on deficiencies in classical complement pathway components. We also discuss the paradox of the link between complement deficiency and lupus. The complement system acts as a 'friend' through the clearance of immune complexes and apoptotic cells, which explains the close association between complement deficiency and lupus. It also acts as an 'enemy' by participating in the effector inflammatory phase of the autoimmune response. Understanding the importance of complement deficiencies should provide novel targets for therapeutic interventions in the modulation of the immune response.

Clinical significance of complement deficiencies

The complement system is composed of more than 30 serum and membrane-bound proteins, all of which are needed for normal function of complement in innate and adaptive immunity. Historically, deficiencies within the complement system have been suspected when young children have had recurrent and difficult-to-control infections. As our understanding of the complement system has increased, many other diseases have been attributed to deficiencies within the complement system. Generally, complement deficiencies within the classical pathway lead to increased susceptibility to encapsulated bacterial infections as well as a syndrome resembling systemic lupus erythematosus. Complement deficiencies within the mannose-binding lectin pathway generally lead to increased bacterial infections, and deficiencies within the alternative pathway usually lead to an increased frequency of Neisseria infections. However, factor H deficiency can lead to membranoproliferative glomerulonephritis and hemolytic uremic syndrome. Finally, deficiencies within the terminal complement pathway lead to an increased incidence of Neisseria infections. Two other notable complement-associated deficiencies are complement receptor 3 and 4 deficiency, which result from a deficiency of CD18, a disease known as leukocyte adhesion deficiency type 1, and CD59 deficiency, which causes paroxysmal nocturnal hemoglobinuria. Most inherited deficiencies of the complement system are autosomal recessive, but properidin deficiency is X-linked recessive, deficiency of C1 inhibitor is autosomal dominant, and mannose-binding lectin and factor I deficiencies are autosomal co-dominant. The diversity of clinical manifestations of complement deficiencies reflects the complexity of the complement system.

The down-stream effects of mannan-induced lectin complement pathway activation depend quantitatively on alternative pathway amplification

Complement activation plays an important role in human pathophysiology. The effect of classical pathway activation is largely dependent on alternative pathway (AP) amplification, whereas the role of AP for the down-stream effect of mannan-induced lectin pathway (LP) activation is poorly understood. In normal human serum specific activation of LP was obtained after exposure to a wide concentration range of mannan on the solid phase. Reaction mechanisms in this system were delineated in inhibition experiments with monoclonal antibodies. Direct mannose-binding lectin (MBL) independent activation of AP was not observed even at high mannan concentrations since addition of the inhibiting anti-MBL mAb 3F8 completely abolished generation of the terminal C5b-9 complex (TCC). However, selective blockade of AP by anti-factor D inhibited more than 80% of TCC release into the fluid phase after LP activation showing that AP amplification is quantitatively responsible for the final effect of initial specific LP activation. TCC generation on the solid phase was distinctly but less inhibited by anti-fD. C2 bypass of the LP pathway could be demonstrated, and AP amplification was also essential during C2 bypass in LP as shown by complete inhibition of TCC generation in C2-deficient serum by anti-fD and anti-properdin antibodies. In conclusion, the down-stream effect of LP activation depends strongly on AP amplification in normal human serum and in the C2 bypass pathway.

Human genetic deficiencies reveal the roles of complement in the inflammatory network: lessons from nature

Complement component C5 is crucial for experimental animal inflammatory tissue damage; however, its involvement in human inflammation is incompletely understood. The responses to gram-negative bacteria were here studied taking advantage of human genetic complement-deficiencies--nature's own knockouts--including a previously undescribed C5 defect. Such deficiencies provide a unique tool for investigating the biological role of proteins. The experimental conditions allowed cross-talk between the different inflammatory pathways using a whole blood model based on the anticoagulant lepirudin, which does not interfere with the complement system. Expression of tissue factor, cell adhesion molecules, and oxidative burst depended highly on C5, mediated through the activation product C5a, whereas granulocyte enzyme release relied mainly on C3 and was C5a-independent. Release of cytokines and chemokines was mediated to varying degrees by complement and CD14; for example, interleukin (IL)-1beta and IL-8 were more dependent on complement than IFN-gamma and IL-6, which were highly dependent on CD14. IL-1 receptor antagonist (IL-1ra) and IFN-gamma inducible protein 10 (IP-10) were fully dependent on CD14 and inversely regulated by complement, that is, complement deficiency and complement inhibition enhanced their release. Granulocyte responses were mainly complement-dependent, whereas monocyte responses were more dependent on CD14. Notably, all responses were abolished by combined neutralization of complement and CD14. The present study provides important insight into the comprehensive role of complement in human inflammatory responses to gram-negative bacteria.

Molecular basis of complete complement C4 deficiency in two North-African families with systemic lupus erythematosus

Complete deficiency of complement C4 is among the strongest genetic risk factors for human systemic lupus erythematosus (SLE). C4 is a constituent of the RP-C4-CYP21-TNX (RCCX) module in the human leukocyte antigen (HLA) that exhibits inter-individual copy-number and gene-size variations. Here, we studied two North-African families with complete C4 deficiency and SLE. The first included a Moroccan male SLE patient (1P) and a sibling, who were both homozygous for HLA-A*02 B*17 DRB1*07. The second had an Algerian female SLE patient (2P) homozygous for HLA-A*01 B*17 DRB1*13. Early SLE disease onset, the presence of photosensitive rashes, anti-Ro/SSA, renal disease and high titers of antinuclear antibodies were the common features of complete C4 deficiency. Southern blot analyses showed that 1P had monomodular RCCX with a long C4A, whereas 2P had bimodular RCCX with one long C4A and one short C4B. Genomic DNA fragments for these mutant genes were amplified and sequenced. A C>T transition that created the R540X nonsense mutation in C4A was found in 1P. An identical 4-bp insertion that generated the Y1537X nonsense mutation was discovered in both C4A and C4B of 2P. The high concordance of SLE and C4 deficiency among patients with non-DR3 and non-DR2 haplotypes underscores the importance of C4 proteins in the protection against SLE.

Risk of non-Hodgkin lymphoma in association with germline variation in complement genes

Germline mutations in complement genes have been associated with susceptibility to infections and autoimmune diseases, conditions that are associated with non-Hodgkin lymphoma (NHL) risk. To test the hypothesis that common genetic variation in complement genes affect risk of NHL, we genotyped 167 single nucleotide polymorphisms (SNPs) from 31 genes in 441 NHL cases and 475 controls. Principal components (PC) and haplotype analyses were used for gene-level tests of NHL risk, while individual SNPs were modelled as having a log-additive effect. In gene level PC analyses, C2 (P = 0.023), C5 (P = 0.0032) and C9 (P = 0.020) were associated with NHL risk; haplotype analyses showed similar results, as well as a haplotype association for C7 (P = 0.046). When all four genes were considered simultaneously, only C5 and C9 remained significant (P < 0.05). In SNP level results from these genes, 10 SNPs had a P < 0.05. However, after correcting for multiple testing, only the C5 SNPs rs7026551 (q = 0.015; OR = 1.54, 95% CI 1.21-1.95) and rs2416810 (q = 0.015; OR = 1.57; 95% CI 1.22-2.01), and the C9 SNP rs187875 (q = 0.015; OR = 0.68; 95% 0.56-0.84) remained noteworthy. Associations were similar for the common NHL subtypes. In summary, we provide evidence for a role of genetic variation in complement genes, particularly C5 and C9, and NHL risk.

General aspects of the genetics of SLE

The application of genetic techniques to the study of systemic lupus erythematosus (SLE) has identified candidate genes with diverse immunological function. There is a growing understanding that susceptibility to SLE is due to a complex interaction of multiple genes and environmental factors, and that many of these may be shared with other autoimmune diseases. In this first of a series of review articles we outline our current understanding of SLE genetics, in particular summarising the results of recent association studies.

Hereditary complement C7 deficiency in nine families: Subtotal C7 deficiency revisited

Deficiencies in terminal complement components, including the component C7, are uncommon and associated with an increased risk of recurrent systemic neisserial infection. A total of 22 molecular defects have been reported in the C7 gene with both complete (C7Q0) and subtotal (C7SD) C7 deficiencies. In this study we report the molecular basis of nine new cases of C7 deficiencies that were characterized by exon-specific sequence analysis. Seven different C7 gene mutations were identified corresponding to small deletions (n=2), splice site changes (n=1) and single base pair substitutions leading to nonsense (n=1) or missense (n=3) mutations. Altogether, three changes of the C7 gene (G357R, R499S and 5' splice donor site of intron 16) account for half of the molecular defects which emphasize that a restricted number of molecular abnormalities are involved in this deficiency. We identified two patients with combined C7Q0/C7SD(R499S) and established the C7SD(R499S) frequency at about 1% in normal Caucasian population. We demonstrated that C7(R499S) mutant protein is retained in the endoplasmic reticulum whereas the wild-type C7 is located in the Golgi apparatus. Our results provide evidence that R499S represents a loss-of-function polymorphism of C7 due to a defective folding of the protein.

Three distinct profiles of serum complement C4 proteins in pediatric systemic lupus erythematosus (SLE) patients: tight associations of complement C4 and C3 protein levels in SLE but not in healthy subjects

The serial changes of serum complement proteins C4 and C3 in SLE were characterized in 33 pediatric SLE patients with defined C4 genotypes. Three distinct groups of C4 protein profiles were observed. The first group was characterized by persistently low C4 levels (<10 mg/dL) throughout the course of the study. Patients with this profile had mild disease manifestations and low to medium copy numbers of C4 genes. The second group featured periodic fluctuations of serum C4 protein concentrations above and below 10 mg/dL, paralleled with ups and downs of SLE disease activities. Most patients with the second profile had unequal copy numbers of C4A and C4B genes and relatively severe disease. The third group had normal serum C4 levels (>15 mg/dL) most of the time and occasionally low C4 and C3 levels that were mostly coincident with disease flares prior to effective medical treatment. Most patients in this group

Which complement assays and typings are necessary for the diagnosis of complement deficiency in patients with lupus erythematosus? A study of 25 patients

INTRODUCTION

Deficiencies in components of the classical pathway of complement activation are strong risk factors for lupus erythematosus (LE).Yet, it has not been addressed whether the conventional measurements of the serum hemolytic CH50 activity and antigenic concentrations of C3 and C4 are sufficient to asses a deficiency in C4A, C4B or C2 components, the most common deficiencies associated with LE.

PATIENTS AND METHODS

In a retrospective series, we performed complement analyses in 35 patients with LE who were systematically screened for a complement deficiency. The majority of patients had cutaneous LE with mild systemic involvement and no complement consumption. Of 25 patients (72%) with complement deficiency we found 13 with a partial C4A deficiency, 2 with a complete C4A deficiency, 6 with a partial C4B deficiency, 2 with a complete C4B deficiency and 2 with a combined partial C2 and C4A deficiency.

RESULTS

The total complement activity (CH50) was decreased in only one out of two patients with complete C4B deficiency. CH50 level was found to be low-normal (35-38 U/ml(-1)) in one patient with partial C4B deficiency, one patient with complete C4B deficiency and both patients with combined partial C4A and C2 deficiency. Total C4 levels were normal in 9 out of 13 the patients with a partial C4A deficiency and in 2 out of 6 patients with a complete C4B deficiency. The antigenic concentration of C3 was low in only 1 patients with a complete C4B deficiency and within the normal range in all the others patients. Overall, 50% of the patients had normal or elevated C3, C4, and CH50 levels.

DISCUSSION

This study emphasizes that the usual measurements of CH50, C3 and C4 levels are not adequate to detect a C4 and/or C2 deficiency in patients with LE. In epidemiologic or investigative studies addressing the prevalence of complement deficiency, more elaborated diagnostic tests, such as C4 protein allotyping, C2 level measurement and genetic screening for type I C2 deficiency should also be performed.

Unraveling the genetics of systemic lupus erythematosus

The capacity to locate polymorphisms on a virtually complete map of the human genome coupled with the ability to accurately evaluate large numbers (by historical standards) of genetic markers has led to gene identification in complex diseases, such as systemic lupus erythematosus (SLE or lupus). While this is a phenotype with enormous clinical variation, the twin studies and the observed familial aggregation, along with the genetic effects now known, suggest a strong genetic component. Unlike type 1 diabetes, lupus genetics is not dominated by the powerful effect of a single locus. Instead, there are at least six known genetic association effects in lupus of smaller magnitude (odds ratio <2), and at least 17 robust linkages (established and arguably confirmed independently) defining potentially responsible genes that largely remain to be discovered. The more convincing genetic associations include the human leukocyte antigen region (with multiple genes), C1q, PTPN22, PDCD1, Fc receptor-like 3, FcgammaRIIA, FcgammaRIIIA, interferon regulatory factor 5, and others. How they contribute to disease risk remains yet to be clarified, beyond the obvious speculation derived from what has previously been learned about these genes. Certainly, they are expected to contribute to lupus risk independently and in combination with each other, with genes not yet identified, and with the environment. A substantial number of genes (>10) are expected to be identified to contribute to lupus or in its many subsets defined by clinical and laboratory features.

Complement deficiency and disease: an update

Complement deficiencies are probably vastly under-diagnosed within clinical medicine. Judging from a Swedish study of C2 deficiency, a deficiency with an estimated prevalence of about 1/20,000 in Western countries, less than 10% of the deficiencies of the classical and alternative pathways and the late complement components are identified in Sweden. C1 inhibitor deficiency and deficiencies of MBL and MASP-2 were not included in the assessment. The introduction of new screening methods should facilitate detection of complement deficiencies in clinical practice. In our study of C2 deficiency (n=40), 57% of the patients had a history of invasive infection with encapsulated bacteria, mainly Streptococcus pneumoniae. This emphasizes the importance of the classical and/or the lectin pathway in defence against severe infection. Rheumatological disease, mainly systemic lupus erythematosus was present in 43% of the patients. In addition, a significant association was found between C2 deficiency and atherosclerosis. Complement-dependent disease mechanisms are discussed together with the potential importance of non-complement genes for disease expression in complement deficiencies. Analysis of larger patient groups is required in order to establish guidelines for investigation and treatment of patients with complement deficiency.

Frequency in Spanish population of familial complement factor 2 type I deficits and associated HLA haplotypes

We present two familial cases of complement factor 2 (C2) type I deficiency. Probands had experienced severe pyogenic bacteria infections in childhood and had undetectable levels of C2 and very low level of CH50. Both children were homozygous for the deletion of 28 bp in exon 6 of the C2 gene. Human leukocyte antigen (HLA) typing in family 1 had the commonly reported associations, but family 2 demonstrated a new association of the mutated C2 gene to HLA-A*3101, -Cw*0602, -B*1801, and -DRB1*0901. In addition, for the first time, the frequency of the 28-bp deletion of C2 and its HLA haplotypic associations have been analyzed in a sample of the Spanish population containing 790 haplotypes and 105 phenotypes. Cw*0602 is frequently found in Spanish haplotypes linked to the C2 mutated gene instead of the commonly reported -Cw*1203. The presence of heterozygous or homozygous individuals for the C2 deletion with low levels of IgD in both families supports the existence of a putative dominant susceptibility gene for IgD deficiency in haplotype HLA-B18, -S042, and -DR2. The frequency of the C2 28-bp deletion in heterozygosis is 1.4% (gene frequency 0.007) in Spanish healthy controls, similar to that reported in other white populations.

Genetics of systemic lupus erythematosus: how far have we come?

There are two primary mechanisms for studying the genetic forces at work in systemic lupus erythematosus (SLE). Several groups have collected large numbers of pedigrees in which multiple family members have SLE for use in linkage studies. These linkage studies serve to isolate areas of the genome in which susceptibility genes lie. Other groups have taken a more direct approach of investigating genes that might contribute to disease pathogenesis in sets of lupus subjects and matched controls. These association studies are accumulating in greater numbers as the technology to determine the genotype at a given locus becomes more accessible. This article discusses the results of both types of studies.

The combination of complement deficiency and cigarette smoking as risk factor for cutaneous lupus erythematosus in men; a focus on combined C2/C4 deficiency

BACKGROUND

Although deficiencies in the early components of the complement system were among the first identified genetic risk factors for systemic lupus erythematosus (SLE), only a few studies addressed their significance in patients with cutaneous LE (CLE). Among environmental factors, it was postulated that cigarette smoking might intervene in the pathogenesis of LE.

OBJECTIVES

To describe the clinical and biological features of patients with CLE and a complement deficiency. A secondary objective was to assess cigarette smoking in patients with CLE.

PATIENTS AND METHODS

A retrospective study including all patients diagnosed as having LE between 1995 and 2003 in the Dermatology Department of Strasbourg University Hospital. Patient charts were reviewed and those patients in whom a C4 and/or C2 deficiency was diagnosed were included. Two patients with a combined C2/C4 deficiency were analysed in detail.

RESULTS

There were 48 females and 37 males (F/M ratio = 1.3), with a mean age of 41 years at diagnosis; 73% of the patients had chronic LE and 27% subacute CLE. Among 32 screened patients, 24 patients with a mean age of 36 years had a complement deficiency; 17 had a C4A deficiency, five a C4B deficiency and two a combined C4A/C2 deficiency. A high proportion (58%) of these patients was male; 82% of the patients were smokers. This was especially true in males: 94% were smokers compared with 69% of females.

CONCLUSIONS

Partial deficiency of C4, C2 or C4 and C2 is a common finding in patients with CLE. Most male patients with CLE are smokers. It is thus suggested that the combination of cigarette smoking and complement deficiency could be a risk factor for LE in men.

Hereditary C2 deficiency in Sweden: frequent occurrence of invasive infection, atherosclerosis, and rheumatic disease

Although frequently asymptomatic, homozygous C2 deficiency (C2D) is known to be associated with severe infections and rheumatic disease. We describe the clinical findings in 40 persons with C2D from 33 families identified in Sweden over 25 years. Medical records covering 96% of the accumulated person-years were reviewed, giving a mean observation time of 39 years (range, 1-77 yr). Severe infection was the predominant clinical manifestation in the cohort: 23 patients had a past history of invasive infections, mainly septicemia or meningitis caused by Streptococcus pneumoniae, and 12 patients had repeated infections of this kind. Nineteen patients had at least 1 episode of pneumonia, and recurrent pneumonia was documented in 10 patients. Repeated infections occurred mainly during infancy and childhood. Systemic lupus erythematosus was found in 10 patients. Another 7 patients had undifferentiated connective tissue disease (n = 4) or vasculitis (n = 3). We found no correlation between susceptibility to invasive infection and rheumatologic disease. Cardiovascular disease occurred at a high rate, with a total of 10 acute myocardial infarctions and 5 cerebrovascular episodes in 6 patients. Causes of death among the C2D patients were infection (n = 5), acute myocardial infarction (n = 3), and cancer (n = 1). We suggest that severe infection may be the principal clinical manifestation of C2D. We also provide novel evidence for a possible role of C2D in the development of atherosclerosis consistent with findings in mannan-binding deficiency and experimental C3 deficiency. In addition, we confirm the well-known association between C2D and systemic lupus erythematosus.

Early manifestation and recognition of C2 complement deficiency in the form of pyogenic infection in infancy

OBJECTIVE

Although frequently asymptomatic, C2 complement component deficiency may lead to severe pyogenic infections or lupus-like illness. In the present report, we describe infectious manifestations in infancy and childhood in our C2-deficient patients.

METHOD

A retrospective study of clinical manifestation in three patients was carried out. C2 deficiency was proved both by undetectable serum C2 level and typical homozygous 28 bp deletion of the C2 gene.

RESULTS

All patients were hospitalized at least once by the age of 12 months, each had one episode of meningitis in infancy, one also had arthritis with septicaemia. Infections of the respiratory tract were the causes of other hospitalizations. Two patients also suffered from frequent mild respiratory tract infections; in both patients, decreased immunoglobulin IgA and immunoglobulin IgG2 or immunoglobulin IgG3 levels were recorded.

CONCLUSION

Our observations point to an early manifestation of C2 deficiency within the first year of life, with meningitis as the most severe complication. The severity of immunodeficiency may be influenced by concomitant deficiencies of immunoglobulin isotypes.

Founder effect of the C9 R95X mutation in Orientals

A nonsense mutation at codon 95 (R95X) in the C9 gene is responsible for most Japanese C9 deficiency (C9D) cases, with a carrier frequency of 6.7%. Upon analysis of microsatellite markers and newly identified dinucleotide repeat number polymorphisms in the 3' flanking region of the C9 gene, a founder effect was demonstrated for the R95X mutation of the C9 gene in Japanese. Screening for the R95X mutation in Korean and Chinese individuals showed that the R95X carrier frequencies in Koreans and Chinese were 2.0% and 1.0%, respectively. Although homozygotes for the R95X mutation were not found in Korea or China, the shared haplotype of the dinucleotide repeat number polymorphisms appeared to be associated with the R95X mutation in the heterozygotes in Korea and China. The founder effect found in East Asians (Japanese, Koreans and Chinese) but not in Caucasians, as well as the haplotype sharing in only a small chromosomal interval, suggested that the R95X mutation of C9 gene was ancient and had occurred after the divergence of East Asians and Caucasians, and before migration of the Yayoi people to Japan. Since the mortality of meningococcal infections in complement-deficient patients is lower than that in normal individuals, a founder effect and a selective advantage in isolation might be the main reasons for the high frequency of the R95X mutation in Japan.

Polymerase chain reaction based C4AQ0 and C4BQ0 genotyping: association with systemic lupus erythematosus in southwest Han Chinese

OBJECTIVE

To investigate the association of complement C4 null genes (C4Q0, including C4AQ0 and C4BQ0) and C2 gene with systemic lupus erythematosus (SLE) in southwest Han Chinese; 136 patients with SLE and 174 matched controls were genotyped.

METHODS

C4 null genes were determined by a polymerase chain reaction (PCR) procedure with sequence specific primers (PCR-SSP). The 2 bp insertion in exon 29, which was previously identified in non-Chinese populations and caused defective C4A genes, was directly typed by sequencing the whole exon 29 using exon specific primers. The exon 6 of complement C2 was also sequenced in both the patients and controls.

RESULTS

The frequency of homozygous C4AQ0 allele was 12.5% (17/136) in patients with SLE compared with 1.1% (2/174) in controls (p<0.001, odds ratio (OR)=12.286, 95% confidence interval (95% CI) 2.786 to 54.170). There was no significant difference for homozygous C4BQ0 allele between patients with SLE and controls (p=0.699). Patients with the C4AQ0 gene had an increased risk of acquiring renal disorder, serositis, and anti-dsDNA antibodies compared with those without C4AQ0 (for renal disorder, p=0.018, OR=8.951, 95% CI 1.132 to 70.804; for serositis, p=0.011, OR 4.891, 95% CI 1.574 to 15.198; for anti-dsDNA, p=0.004, OR 7.630, 95%CI 1.636 to 35.584). None of the patients or controls had the 2 bp insertion in exon 29 of the C4 gene. The type I C2 deficiency was not detected in the 310 samples.

CONCLUSION

It is suggested that deficiency of C4A (not due to a 2 bp insertion in exon 29), but not C4B or C2, may be a risk factor for acquiring SLE in south west Han Chinese; this results in increased risk of renal disorder, serositis, and anti-dsDNA antibodies in patients with SLE. Racial differences seem to be relevant in susceptibility to SLE