Complement component C6 deficiency and susceptibility to Neisseria Meningitidis infection

Meningococcal disease remains one of the most serious bacterial infections in both Western and developing countries. Despite recent advances in treatment the mortality rate remains at about 12%.1 There is a group of South Africans who are particularly vulnerable to this disease. They are individuals with genetically determined deficiencies of individual terminal complement proteins, in particular of the sixth component of complement (C6).2 The human complement system forms part of the humeral immune system and consists of a series of proteins.3 The interaction of antigen (such as components of bacterial outer membranes) and antibody leads to activation of the first component C1q, and consequent activation of part or all of the complement cascade. This has a number of biological effects including the formation on the membrane of the membrane attack complex (MAC) from components C5b, C6, C7, C8 and C9. The MAC is able to mediate lysis of some mammalian cells such as red blood cells, as well as lysis of bacteria and certain viruses. This action of complement has been recognised for many years as playing a major role in defence against infection.4 In addition, MAC action is often sublytic on nucleated host cells, and this interaction can sometimes stimulate cellular biosynthesis and act in a pro-inflammatory manner.5 Many other complement proteins, and products of complement activation, also interact with the cellular immune system and the inflammatory system. If activation is caused by pathological processes such as ischaemia, complement can be an important contributor to host tissue necrosis.6 The effects of complement activation are very complex and can be detrimental as well as beneficial

Complement component C5 and C6 mutation screening indicated in meningococcal disease in South Africa

BACKGROUND: Invasive meningococcal disease (MD), caused by Neisseria meningitidis infection, is endemic in South Africa, with a seasonal peak in winter and spring. There were 2 432 laboratory-confirmed cases between 2006 and 2010. Human deficiency of the fifth complement component (C5D) or complete absence of the sixth component (C6Q0) leads to increased risk of MD, which is often recurrent. All attacks are serious and can lead to death or severe long-term consequences. OBJECTIVE: To determine the frequency of specific disease-associated C5 and C6 gene mutations in patients presenting with MD in the Western Cape. RESULTS: In 109 patients with confirmed invasive MD investigated for local mutations known to cause C5D and C6Q0, 3 were C5D and 11 were C6Q0. In 46 black patients tested, 3 were C5D and 7 were C6Q0. In 63 coloured patients, none were C5D and 4 were C6Q0. All deficient patients were followed up and offered prophylaxis. CONCLUSION: C5D and C6Q0 are not rare genetic diseases in South Africa and affected patients are susceptible to repeated MD; 12.8% of MD patients tested were C5D or C6Q0. Blacks were at greatest risk with 21.7% being either C5D or C6Q0. We strongly recommend diagnostic testing for complement C5 and C6 deficiency in the routine work-up of all MD cases in South Africa. Prophylactic treatment should be started in susceptible individuals

Screening for complement deficiency

Complement (C) deficiencies are not common and laboratory screening for clinical reasons generally involves examining relatively few samples. Nevertheless, because of the range of tests, complete testing may mean carrying out many different assays. In contrast, the determination of the prevalence of genetic complement deficiencies in populations requires a very few specific methods that are suitable for dealing with a large number of samples

An abnormal but functionally active complement component c9 protein found in an irish family with subtotal c9 deficiency

Two independently segregating C9 genetic defects have previously been reported in two siblings in an Irish family with subtotal C9 deficiency. One defect would lead to an abnormal C9 protein, with replacement of a cysteine by a glycine (C98G). The second defect is a premature stop codon at amino acid 406 which would lead to a truncated C9. However, at least one of two abnormal proteins was present in the circulation of the proband at 0.2% of normal C9 concentration. In this study, the abnormal protein was shown to have a molecular weight approximately equal to that of normal C9, and to carry the binding site for monoclonal antibody (mAb) Mc42 which is known to react with an epitope at amino acid positions 412-426, distal to 406. Therefore, the subtotal C9 protein carries the C98G defect. The protein was incorporated into the terminal complement complex, and was active in haemolytic, bactericidal and lipopolysaccharide release assays. A quantitative haemolytic assay indicated even slightly greater haemolytic efficiency than normal C9. Epitope mapping with six antihuman C9 mAbs showed the abnormal protein to react to these antibodies in the same way as normal C9. However, none of these mAbs have epitopes within the lipoprotein receptor A module, where the C98G defect is located. The role of this region in C9 functionality is still unclear. In conclusion, we have shown that the lack of a cysteine led to the production of a protein present in the circulation at very much reduced levels, but which was fully functionally active

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.This study was funded by Instituto de Salud Carlos III, grant PI14/00405, co‐financed by the European Regional Development Fund (ERDF), and by MINECO grant CGL2013‐44351‐

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.This study was funded by Instituto de Salud Carlos III, grant PI14/00405, co‐financed by the European Regional Development Fund (ERDF), and by MINECO grant CGL2013‐44351‐

Characterization of a large genomic deletion in four Irish families with C7 deficiency

Inherited deficiency of the seventh complement component (C7) is associated with increased susceptibility to Neisseria meningitidis infections. The disease is rare in most Western countries. Here we report new investigations of alarge, but incompletely characterized genomicdeletion of exons 8 and 9 [c.739-?_1093+?del], previously identified in three unrelated Irishfamilies with C7deficiency. We have analysed DNA from one individual, who is homozygous for the deletion, by PCR using primers progressively proximal to the deleted exons. Thus we were able to map the deletion boundaries. Amplification across the breakpoint and sequencing revealed an indel mutation that included a 6.4 kb deletion together with an insertion of a novel 8 bp sequence [c.739+1262_1270-2387delinsGCAGGCCA]. We demonstrated the same defect in the C7 deficient patients from each family and developed a duplex PCR method to enable the detection of alleles containing the deletion in heterozygotes. A member of a fourth family was found to be homozygous for the deletion defect. Thus, the deletion defect may be a more commonly distributed cause of C7deficiency in Ireland

Complement component C5 and C6 mutation screening indicated in meningococcal disease in South Africa

BACKGROUND: Invasive meningococcal disease (MD), caused by Neisseria meningitidis infection, is endemic in South Africa, with a seasonal peak in winter and spring. There were 2 432 laboratory-confirmed cases between 2006 and 2010. Human deficiency of the fifth complement component (C5D) or complete absence of the sixth component (C6Q0) leads to increased risk of MD, which is often recurrent. All attacks are serious and can lead to death or severe long-term consequences. OBJECTIVE: To determine the frequency of specific disease-associated C5 and C6 gene mutations in patients presenting with MD in the Western Cape. RESULTS: In 109 patients with confirmed invasive MD investigated for local mutations known to cause C5D and C6Q0, 3 were C5D and 11 were C6Q0. In 46 black patients tested, 3 were C5D and 7 were C6Q0. In 63 coloured patients, none were C5D and 4 were C6Q0. All deficient patients were followed up and offered prophylaxis. CONCLUSION: C5D and C6Q0 are not rare genetic diseases in South Africa and affected patients are susceptible to repeated MD; 12.8% of MD patients tested were C5D or C6Q0. Blacks were at greatest risk with 21.7% being either C5D or C6Q0. We strongly recommend diagnostic testing for complement C5 and C6 deficiency in the routine work-up of all MD cases in South Africa. Prophylactic treatment should be started in susceptible individuals