Two Mutations of the C7 Gene, c.1424G > A and c.281-1G > T, in Two Korean Families

Genetic bases of C7 deficiency: systematic review and report of a novel deletion determining functional hemizygosity

Primary complement system (C) deficiencies are rare but notably associated with an increased risk of infections, autoimmunity, or immune disorders. Patients with terminal pathway C-deficiency have a 1,000- to 10,000-fold-higher risk of Neisseria meningitidis infections and should be therefore promptly identified to minimize the likelihood of further infections and to favor vaccination. In this paper, we performed a systematic review about clinical and genetic patterns of C7 deficiency starting from the case of a ten-year old boy infected by Neisseria meningitidis B and with clinical presentation suggestive of reduced C activity. Functional assay via Wieslab ELISA Kit confirmed a reduction in total C activity of the classical (0.6% activity), lectin (0.2% activity) and alternative (0.1% activity) pathways. Western blot analysis revealed the absence of C7 in patient serum. Sanger sequencing of genomic DNA extracted from peripheral blood of the patient allowed the identification of two pathogenetic variants in the C7 gene: the already well-characterized missense mutation G379R and a novel heterozygous deletion of three nucleotides located at the 3'UTR (c.*99_*101delTCT). This mutation resulted in an instability of the mRNA; thus, only the allele containing the missense mutation was expressed, making the proband a functional hemizygote for the expression of the mutated C7 allele.

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.

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.

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.