High prevalence of complement component C6 deficiency among African-Americans in the south-eastern USA

Moyamoya Disease Associated with a Deficiency of Complement Component 6

OBJECTIVES

Complement component 6 (C6) deficiency is a very rare genetic defect that leads to significantly diminished synthesis, secretion, or function of C6. In the current report, we demonstrate a previously undescribed, homozygous missense mutation in exon 17 of the C6 gene (c.2545A>G p.Arg849Gly) in a 35-year-old Japanese woman with moyamoya disease and extremely low levels of CH50 (<7.0 U/mL).

MATERIALS AND METHODS

The complement gene analysis using hybridization capture-based next generation sequencing was performed. CH50 was determined in patient's plasma mixed with plasma from a healthy donor or purified human C6 protein. Western blot was performed on patient's plasma using polyclonal antibodies against C6, with healthy donor's plasma and purified human C6 protein as positive controls while C6-depleted human serum as a negative control. The carriage of ring finger protein 213 variant (c.14576G>A p.Arg4859Lys), a susceptibility gene for moyamoya disease, was examined by direct sequencing.

RESULTS

CH50 mixing test clearly showed a deficiency pattern, being rescued by addition of only 1% healthy donor's plasma or 1 μg/mL purified human C6 protein (1/50-1/100 of physiological concentration). Western blot revealed the absence of C6 protein in the patient's plasma, confirming a quantitative deficiency of C6. The ring finger protein 213 variant was not detected.

CONCLUSIONS

Our data implies that unrecognized complement deficiencies would be harbored in cerebrovascular diseases with unknown etiologies.

Comprehensive Update and Revision of Nomenclature on Complement C6 and C7 Variants

Complement genes encompass a wide array of variants, giving rise to numerous protein isoforms that have often been shown to exhibit clinical significance. Given that these variants have been discovered over a span of 50 y, one challenging consequence is the inconsistency in the terminology used to classify them. This issue is prominently evident in the nomenclature used for complement C6 and C7 variants, for which we observed a great discrepancy between previously published works and variants described in current genome browsers. This report discusses the causes for the discrepancies in C6 and C7 nomenclature and seeks to establish a classification system that would unify existing and future variants. The inconsistency in the methods used to annotate amino acids and the modifications pinpointed in the C6 and C7 primers are some of the factors that contribute greatly to the discrepancy in the nomenclature. Several variants that were classified incorrectly are highlighted in this report, and we showcase first-hand how a unified classification system is important to match previous with current genetic information. Ultimately, we hope that the proposed classification system of nomenclature becomes an incentive for studies on complement variants and their physiological and/or pathological effects.

An immune gene signature to predict prognosis and immunotherapeutic response in lung adenocarcinoma

Lung adenocarcinoma is one of the most common malignant tumors worldwide. The purpose of this study was to construct a stable immune gene signature for prediction of prognosis (IGSPP) and response to immune checkpoint inhibitors (ICIs) therapy in LUAD patients. Five genes were screened by weighted gene coexpression network analysis, Cox regression and LASSO regression analyses and were used to construct the IGSPP. The survival rate of the IGSPP low-risk group was higher than that of the IGSPP high-risk group. Multivariate Cox regression analysis showed that IGSPP could be used as an independent prognostic factor for the overall survival of LUAD patients. IGSPP genes were enriched in cell cycle pathways. IGSPP gene mutation rates were higher in the high-risk group. CD4 memory-activated T cells, M0 and M1 macrophages had higher infiltration abundance in the high-risk group, which was associated with poor overall survival. In contrast, the abundance of resting CD4 memory T cells, monocytes, resting dendritic cells and resting mast cells associated with a better prognosis was higher in the low-risk group. TIDE scores and the expressions of different immune checkpoints showed that patients in the high-risk IGSPP group benefited more from ICIs treatment. In short, an IGSPP of LUAD was constructed and characterized. It could be used to predict the prognosis and benefits of ICIs treatment in LUAD patients.

Genetic workup as a complementary tool for the diagnosis of primary complement component deficiencies: a multicenter experience

Diagnosis of primary complement deficiencies requires a high index of suspicion. Thus, susceptible patients are often underdiagnosed and untreated. Here, we present a multicenter experience with two novel inborn errors of the classical complement system. This is a retrospective multicenter analysis of computerized medical records of children (<18 years) admitted in the period between 2012 and 2018 at Shaare Zedek Medical Center in Jerusalem and Edmond and Lily Safra Children's Hospital, Tel-Hashomer Medical Center, in Ramat Gan, Israel. Patients were genetically diagnosed by a complementary immune workup. We identified 5 patients (3 males) from four different families harboring two novel mutations in the complement components C6-C8. Genetic mutations were identified by whole-exome sequencing or by sequencing of the coding exons of a single gene based on the findings in the immune workup. Clinical manifestations consisted of meningitis with or without meningococcemia. The immune workup demonstrated nearly absent levels of CH50, compatible with a complement pathway defect. Diagnosis delay ranged between 0 and 30 years.

CONCLUSION

Awareness of risk factors for primary complement deficiencies, even at the first infectious episode, should facilitate prompt immune and genetic workup, commencing diagnosis and proper treatment for the patient and family.

WHAT IS KNOWN

• Deficiencies in the classical terminal complement components increase susceptibility to invasive meningococcal infections. • Recurrent meningococcal infections mandate a diagnostic workup of the complement system.

WHAT IS NEW

• Genetic workup can be utilized for prompt diagnosis of complement deficiencies. • High rates of consanguinity, even in the presence of a single meningococcal infection, should promote immune and genetic workups.

Novel pathogenic mutations identified in the first Chinese pedigree of complete C6 deficiency

Objectives

Complete C6 deficiency (C6Q0) is a rare primary immunodeficiency leading to increased susceptibility to recurrent Neisseria infections. Patients with C6Q0 have mostly been reported in individuals of African ancestry previously, but never in Chinese. We identify the first Chinese patients with C6Q0 through family screening of an index case presenting with recurrent Neisseria meningitis with septicaemia and performed extensive clinical, serological and genetic investigations.

Methods

Two variants in C6 were identified by next‐generation sequencing and confirmed by Sanger sequencing in an index case of C6Q0. Immunological investigations, complement haemolytic assays (CH50/AH50), C6 gene sequencing and quantification of serum C6 levels were performed for all available members of his nonconsanguineous family.

Results

Three C6Q0 patients were identified with near‐absent C6 levels, absent CH50/AH50 activity and compound heterozygous for two nonsense mutations in the C6 gene: NM_000065.4:c.1786C>T (p.Arg596Ter) and NM_000065.4:c.1816C>T (p.Arg606Ter). Neither mutations have been reported to be pathogenic previously. Two other family members who were heterozygous for either p.Arg596Ter or and p.Arg606Ter had intermediate C6 levels but preserved CH50/AH50 activity. These two loss‐of‐function mutations showed a strong genotype–phenotype correlation in C6 levels.

Conclusions

We report on two compound heterozygous mutations in C6, p.Arg596Ter and p.Arg606Ter inherited in three patients of the first recorded Chinese pedigree of C6Q0. Neither mutations had been reported to be pathogenic previously. We demonstrate that heterozygous family members with subtotal C6 levels had preserved complement haemolytic function and demonstrate a threshold effect of C6 protein level.

Delayed Generalized Necrotic Purpuric Rash in a C6-deficient 12-year-old Girl Treated for Group W Meningococcal Disease

We report an unusual case of generalized necrotic purpuric rash that started 48 hours after the initiation of effective third-generation cephalosporin therapy to treat Neisseria meningitidis W infection in a 12-year-old girl. The course was favorable with no shock, and she recovered completely without sequelae. This infection revealed C6 deficiency in our patient.

Hierarchical genomic analysis of carried and invasive serogroup A Neisseria meningitidis during the 2011 epidemic in Chad

Background

Serogroup A Neisseria meningitidis (NmA) was the cause of the 2011 meningitis epidemics in Chad. This bacterium, often carried asymptomatically, is considered to be an “accidental pathogen”; however, the transition from carriage to disease phenotype remains poorly understood. This study examined the role genetic diversity might play in this transition by comparing genomes from geographically and temporally matched invasive and carried NmA isolates.

Results

All 23 NmA isolates belonged to the ST-5 clonal complex (cc5). Ribosomal MLST comparison with other publically available NmA:cc5 showed that isolates were closely related, although those from Chad formed two distinct branches and did not cluster with other NmA, based on their MLST profile, geographical and temporal location. Whole genome MLST (wgMLST) comparison identified 242 variable genes among all Chadian isolates and clustered them into three distinct phylogenetic groups (Clusters 1, 2, and 3): no systematic clustering by disease or carriage source was observed. There was a significant difference (p = 0.0070) between the mean age of the individuals from which isolates from Cluster 1 and Cluster 2 were obtained, irrespective of whether the person was a case or a carrier.

Conclusions

Whole genome sequencing provided high-resolution characterization of the genetic diversity of these closely related NmA isolates. The invasive meningococcal isolates obtained during the epidemic were not homogeneous; rather, a variety of closely related but distinct clones were circulating in the human population with some clones preferentially colonizing specific age groups, reflecting a potential age-related niche adaptation. Systematic genetic differences were not identified between carriage and disease isolates consistent with invasive meningococcal disease being a multi-factorial event resulting from changes in host-pathogen interactions along with the bacterium.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3789-0) contains supplementary material, which is available to authorized users.

Complement factor 5 (C5) p.A252T mutation is prevalent in, but not restricted to, sub-Saharan Africa: implications for the susceptibility to meningococcal disease

Complement C5 deficiency (C5D) is a rare primary immunodeficiency associated with recurrent infections, particularly meningitis, by Neisseria species. To date, studies to elucidate the molecular basis of hereditary C5D have included fewer than 40 families, and most C5 mutations (13 of 17) have been found in single families. However, the recently described C5 p.A252T mutation is reported to be associated with approximately 7% of meningococcal disease cases in South Africa. This finding raises the question of whether the mutation may be prevalent in other parts of Africa or other continental regions. The aim of this study was to investigate the prevalence of C5 p.A252T in Africa and other regions and discuss the implications for prophylaxis against meningococcal disease. In total, 2710 samples from healthy donors within various populations worldwide were analysed by quantitative polymerase chain reaction (qPCR) assay to detect the C5 p.A252T mutation. Eleven samples were found to be heterozygous for p.A252T, and nine of these samples were from sub-Saharan African populations (allele frequency 0·94%). Interestingly, two other heterozygous samples were from individuals in populations outside Africa (Israel and Pakistan). These findings, together with data from genomic variation databases, indicate a 0·5-2% prevalence of the C5 p.A252T mutation in heterozygosity in sub-Saharan Africa. Therefore, this mutation may have a relevant role in meningococcal disease susceptibility in this geographical area.

Meningococcal disease and the complement system

Despite considerable advances in the understanding of the pathogenesis of meningococcal disease, this infection remains a major cause of morbidity and mortality globally. The role of the complement system in innate immune defenses against invasive meningococcal disease is well established. Individuals deficient in components of the alternative and terminal complement pathways are highly predisposed to invasive, often recurrent meningococcal infections. Genome-wide analysis studies also point to a central role for complement in disease pathogenesis. Here we review the pathophysiologic events pertinent to the complement system that accompany meningococcal sepsis in humans. Meningococci use several often redundant mechanisms to evade killing by human complement. Capsular polysaccharide and lipooligosaccharide glycan composition play critical roles in complement evasion. Some of the newly described protein vaccine antigens interact with complement components and have sparked considerable research interest.

Complement component C6 deficiency in a Spanish family: implications for clinical and molecular diagnosis

Complement component C6 deficiency is a genetic disease presenting as increased susceptibility to invasive Neisseria meningitidis infections. This disorder has rarely been diagnosed in the Spanish population. In this work we report the immunochemical and molecular characterization of complement C6 deficiency in a Spanish patient showing no detectable functional activity of either the classical or alternative complement pathways and reporting a history of several episodes of meningococcal meningitis. The levels of individual complement components C3, C4, C5, C7, C8 and C9 were within the normal range. However, C6 level was low in the patient's serum as measured by radial immunodiffusion. Exon-specific polymerase chain reaction and sequencing of the C6 gene revealed a previously described homozygous single base deletion in exon 6 (c.821delA), leading to a shift in the reading frame that caused the generation of a downstream stop codon, which, in turn, provoked the truncation of the C6 protein (p.Gln274fs). To our knowledge, this is the first report on the c.821delA mutation in the Spanish population, which has previously only been identified in individuals of African ancestry. Characterization of this mutation was thought interesting in order to elucidate its source and help understand the molecular basis of this uncommon deficiency in our population. Moreover, this report highlights the importance of complement screening in cases of repeated meningococcal infections in order to establish its involvement and to consider adequate clinical recommendations such as prophylactic antibiotics or meningococcal vaccines and, subsequently, for genetic counselling.

The C5 convertase is not required for activation of the terminal complement pathway in murine experimental cerebral malaria

Cerebral malaria (CM) is the most severe manifestation of clinical malaria syndromes and has a high fatality rate especially in the developing world. Recent studies demonstrated that C5(-/-) mice are resistant to experimental CM (ECM) and that protection was due to the inability to form the membrane attack complex. Unexpectedly, we observed that C4(-/-) and factor B(-/-) mice were fully susceptible to disease, indicating that activation of the classical or alternative pathways is not required for ECM. C3(-/-) mice were also susceptible to ECM, indicating that the canonical C5 convertases are not required for ECM development and progression. Abrogation of ECM by treatment with anti-C9 antibody and detection of C5a in serum of C3(-/-) mice confirmed that C5 activation occurs in ECM independent of C5 convertases. Our data indicate that activation of C5 in ECM likely occurs via coagulation enzymes of the extrinsic protease pathway.

Digestive vacuole of Plasmodium falciparum released during erythrocyte rupture dually activates complement and coagulation

Severe Plasmodium falciparum malaria evolves through the interplay among capillary sequestration of parasitized erythrocytes, deregulated inflammatory responses, and hemostasis dysfunction. After rupture, each parasitized erythrocyte releases not only infective merozoites, but also the digestive vacuole (DV), a membrane-bounded organelle containing the malaria pigment hemozoin. In the present study, we report that the intact organelle, but not isolated hemozoin, dually activates the alternative complement and the intrinsic clotting pathway. Procoagulant activity is destroyed by phospholipase C treatment, indicating a critical role of phospholipid head groups exposed at the DV surface. Intravenous injection of DVs caused alternative pathway complement consumption and provoked apathy and reduced nociceptive responses in rats. Ultrasonication destroyed complement-activating and procoagulant properties in vitro and rendered the DVs biologically inactive in vivo. Low-molecular-weight dextran sulfate blocked activation of both complement and coagulation and protected animals from the harmful effects of DV infusion. We surmise that in chronic malaria, complement activation by and opsonization of the DV may serve a useful function in directing hemozoin to phagocytic cells for safe disposal. However, when the waste disposal system of the host is overburdened, DVs may transform into a trigger of pathology and therefore represent a potential therapeutic target in severe malaria.

Disease-causing mutations in genes of the complement system

Recent studies have revealed profound developmental consequences of mutations in genes encoding proteins of the lectin pathway of complement activation, a central component of the innate immune system. Apart from impairment of immunity against microorganisms, it is known that hereditary deficiencies of this system predispose one to autoimmune conditions. Polymorphisms in complement genes are linked to, for example, atypical hemolytic uremia and age-dependent macular degeneration. The complement system comprises three convergent pathways of activation: the classical, the alternative, and the lectin pathway. The recently discovered lectin pathway is less studied, but polymorphisms in the plasma pattern-recognition molecule mannan-binding lectin (MBL) are known to impact its level, and polymorphisms in the MBL-associated serine protease-2 (MASP-2) result in defects of complement activation. Recent studies have described roles outside complement and immunity of another MBL-associated serine protease, MASP-3, in the etiology of 3MC syndrome, an autosomal-recessive disorder involving a spectrum of developmental features, including characteristic facial dysmorphism. Syndrome-causing mutations were identified in MASP1, encoding MASP-3 and two additional proteins, MASP-1 and MAp44. Furthermore, an association was discovered between 3MC syndrome and mutations in COLEC11, encoding CL-K1, another molecule of the lectin pathway. The findings were confirmed in zebrafish, indicating that MASP-3 and CL-K1 underlie an evolutionarily conserved pathway of embryonic development. Along with the discovery of a role of C1q in pruning synapses in mice, these recent advances point toward a broader role of complement in development. Here, we compare the functional immunologic consequences of "conventional" complement deficiencies with these newly described developmental roles.

Complement deficiency states and associated infections

A major function of the immune system is to protect the host from microbial infections. The complement system plays important roles in both the innate and the adaptive immune defense and also acts as a bridge between these arms of immunity. This is obvious from complement deficiencies which in varying degree, depending on which factor is missing, are associated with increased infection susceptibility and also increased risk for other, mainly autoimmune diseases. Genetically determined deficiencies are described for almost all complement proteins but the consequences show a wide variation. Here the genetic defects and molecular abnormalities in complement deficient persons, related clinically relevant infections and the options for prevention and therapy are reviewed. The roles of complement in host defense against common infections are also discussed.

Lymphocyte subsets, immunoglobulin levels, complement activity CH50, and phagocytic peroxide production in 19 Iranian patients with first episode of bacterial meningitis

BACKGROUND

Despite the availability of potent antimicrobial drugs, bacterial meningitis remains a serious infection with significant morbidity and mortality. In many studies, pyogenic meningitis is reported in patients with immunoglobulin (Ig) and complement deficiencies. In the present study, a broad range of immunological tests were performed to determine the relative importance of primary immunodeficiency as a predisposing cause of first episode of pyogenic meningitis without any evidence of other major infections in past medical history.

METHODS

We studied 19 patients with bacterial meningitis confirmed by smear, culture, and cerebrospinal fluid parameters. Immunological tests were performed within 1 to 21 days of diagnosis. Twenty healthy adults served as controls. Serum Ig levels (IgA, IgG, IgM, IgE) and total hemolytic complement (CH5O) as screening tests were done. Lymphocytes, neutrophils, and T-cells were enumerated. Nitroblue tetrazolium test was used for the assessment of neutrophil function.

RESULTS

Thirteen patients were male and six were female. The mean age of the patients was 27.8 ± 19 years (range 5-73 years). One patient had subnormal IgA levels; five patients had subnormal IgE levels; one patient had lymphopenia and low CD4, CD3, and CD19; and one patient had subnormal IgM and IgE levels with lymphopenia and low CD4, CD3, CD8, and CD19 counts. All patients had normal complement components (C3 and C4), CH50, and nitroblue tetrazolium test.

CONCLUSION

The most common immunodeficiency in our study was Ig deficiency. Our results support the recommendation that immunological evaluation, especially Ig assay, should be used in patients with bacterial meningitis even in the first episode.

Epidemic meningitis due to Group A Neisseria meningitidis in the African meningitis belt: a persistent problem with an imminent solution

Epidemic meningitis in Africa remains an important and unresolved public health problem. Bacteriologic and epidemiologic data collected over the past 30 years have consistently established the importance of Group A Neisseria meningitidis as the dominant etiologic agent. The meningococcal Group A capsule is the major virulence factor; it is a polysaccharide comprised of a repeating unit of partly O-acetylated alpha-1,6-linked N-acetylmannosamine phosphate. Meningitis epidemics occur annually during the dry season (January to May) and stop with the first rains. Until now, control of these meningitis epidemics has relied on a reactive vaccination strategy with polysaccharide vaccines that is logistically complicated and has not put an end to recurrent epidemics. A meningococcal A conjugate vaccine (MenAfriVac) has been developed and tested in Phase II clinical trials in Africa. The vaccine has been shown to be safe and to generate a sustained immunologic response with functional antibody 20 times higher than that seen with polysaccharide vaccine. Widespread use of such a vaccine is likely to generate herd immunity and to put an end to Group A meningococcal epidemics.

State-based surveillance to determine trends in meningococcal disease

OBJECTIVES

Meningococcal disease (MD), is a leading cause of meningitis in the U.S. The purpose of this study was to determine the epidemiology of MD in Oklahoma, including trends, high-risk populations, and outcomes.

METHODS

Cases from the statewide passive reporting system with disease onset between 1988 and 2004 were included; 2002-2004 cases were linked to hospital discharge data. We performed a multivariate logistic regression of variables predicting death.

RESULTS

There were 545 total cases (mean annual incidence rate 1.0/100,000); 13% died. Rates were highest for children younger than 2 years of age; black males had rates two times higher than the state rate and a different age distribution than other race-gender groups. Mean length of hospital stay was 12 days and mean charges were $37,724. For every 10 years of age, the risk of death increased 13% (adjusted odds ratio 1.13, 95% confidence interval [CI] 1.05, 1.22). People younger than age 40 who developed MD between October and February were 68% more likely to die than those who developed it in other months (rate ratio [RR] 1.68, 95% CI 1.39, 2.05); an increased risk of death during these months was not statistically significant in people aged 40 and older (RR 1.19, 95% CI 0.83, 1.69).

CONCLUSION

Using statewide public health surveillance data to characterize the epidemiology of MD is important to understand local trends and risk factors.

Prevalence of mutations leading to complete C6 deficiency (C6Q0) in the Western Cape, South Africa and detection of novel mutations leading to C6Q0 in an Irish family

Complement component C6 is one of five terminal complement components incorporated into the membrane attack complex. Complete deficiency of C6 (C6Q0) leads to an increased susceptibility to Neisseria meningitidis infections, and affected individuals typically present with recurrent meningococcal disease. There is a relatively high prevalence of C6Q0 in the Western Cape, South Africa and three frameshift mutations have previously been described to be responsible for C6Q0 in this area-879delG, 1195delC, and 1936delG (current nomenclature). We have now genotyped a further nine genetically independent individuals with C6Q0, confirming previous reports that the most common defect in the Western Cape is 879delG. Moreover, we report the first identification of the 878delA mutation within the Western Cape, which has previously only been reported in individuals of African descent living in the United States or Europe. We also investigated the genotype of an Irish C6Q0 individual and her sibling, and report two previously undescribed mutations. One mutation alters a tyrosine codon to a stop codon within exon 10. The second mutation is within the 5' donor splice site of intron 3, and would, in all probability, disrupt splicing. These two mutations were shown to segregate independently. We also discuss the nomenclature for reporting C6 and C7 gene mutations, as the current nomenclature does not follow the recognised guidelines.

[Neisseria meningitidis infection. Clinical criteria orienting towards a deficiency in the proteins of the complement]

OBJECTIVE

Complement protein deficiency of the classical pathway or in proteins of the alternate pathway is rare but considerably increase the risk of infection with Neisseria meningitidis. The aim of this study was to determine the clinical criteria of the group at risk.

METHODS

Retrospective study of the clinical and biological data of patients exhibiting complement protein deficiency associated with one or several N. meningitidis infections.

RESULTS

Forty cases were studied, including 35 classical pathway protein deficiencies, with a predominance of C7 deficiency, 3 properdin deficiencies and 2 acquired C3 deficiencies. More than 60% of the patients exhibited recurrent N. meningitidis infections. Serogroups of rare strains were isolated in 50% of cases. Properdin deficiency was associated with a fulminating form in 2 cases out of 3. The age at onset of the first manifestations varied from 2 months to 32 years.

CONCLUSION

A deficiency must be systematically searched for in all patients presenting with a N. meningitidis infection before the age of 6 months or after the age of 5 years. Identification of deficient patients permits the proposal of family screening and appropriate prophylaxis, including preventive vaccination.

Restricted genetic defects underlie human complement C6 deficiency

Complement C6 homozygous deficiency (C6D) has been rarely observed in Caucasians but was reported at higher prevalence among African-Americans. We report on the molecular basis of C6D in seven unrelated black individuals of North or Central Africa descent who live in France. These patients have presented Neisseria meningitidis infection (four cases), focal and segmental glomerulosclerosis with hyalinosis (one case), systemic lupus erythematosus (one case) or Still's disease (one case). All patients exhibited undetectable antigenic C6 by using a sensitive ELISA assay. An additional four cases of complete C6 deficiency with no associated disease have been characterized after family studies. Exons 6, 7 and 12 have been described recently as the location of molecular defects on the C6 gene in randomly chosen black Americans. Genomic DNA from the seven patients were subjected to direct polymerase chain reaction amplification of these three exons. Nucleotide sequencing analysis of the amplified DNA fragments revealed a homozygous single-base deletion (1936delG) in exon 12 in three cases and four compound heterozygous deletions for a single base in exon 7 (1195delC) or in exon 6 (878delA) associated with the same deletion in exon 12 (1936delG). Our observations further establish the restricted pattern of genetic defects associated with homozygous C6 complement deficiency in individuals of African descent.