title: Assessment of complement C4 gene copy number using the paralog ratio test.
abstract: The complement C4 locus is in the class III region of the MHC, and exhibits copy number variation. Complement C4 null alleles have shown association with a number of diseases including systemic lupus erythematosus (SLE). However, most studies to date have used protein immunophenotyping and not direct interrogation of the genome to determine C4 null allele status. Moreover, a lack of accurate C4 gene copy number (GCN) estimation and tight linkage disequilibrium across the disease-associated MHC haplotypes has confounded attempts to establish whether or not these associations are causal. We have therefore developed a high throughput paralog ratio test (PRT) in association with two restriction enzyme digest variant ratio tests (REDVRs) to determine total C4 GCN, C4A GCN, and C4B GCN. In the densely genotyped CEU cohort we show that this method is accurate and reproducible when compared to gold standard Southern blot copy number estimation with a discrepancy rate of 9%. We find a broad range of C4 GCNs in the CEU and the 1958 British Birth Cohort populations under study. In addition, SNP-C4 CNV analyses show only moderate levels of correlation and therefore do not support the use of SNP genotypes as proxies for complement C4 GCN.
authors.affiliation: Section of Rheumatology, Faculty of Medicine, Imperial College London, London, United Kingdom.
authors.forename: Michelle M A
authors.initials: MM
authors.lastname: Fernando
authors.forename: Lora
authors.initials: L
authors.lastname: Boteva
authors.forename: David L
authors.initials: DL
authors.lastname: Morris
authors.forename: Bi
authors.initials: B
authors.lastname: Zhou
authors.forename: Yee Ling
authors.initials: YL
authors.lastname: Wu
authors.forename: Marja-Liisa
authors.initials: ML
authors.lastname: Lokki
authors.forename: Chack Yung
authors.initials: CY
authors.lastname: Yu
authors.forename: John D
authors.initials: JD
authors.lastname: Rioux
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Hollox
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Vyse
mesh_terms: D000483:Alleles; D003181:Complement C4 / Q000235:genetics*; D018628:Gene Dosage; D005787:Gene Frequency; D056726:Genetic Association Studies / Q000379:methods; D005838:Genotype; D006239:Haplotypes / Q000235:genetics*; D006801:Humans; D015810:Linkage Disequilibrium; D008180:Lupus Erythematosus, Systemic / Q000235:genetics; D008285:Major Histocompatibility Complex / Q000235:genetics; D009154:Mutation; D020641:Polymorphism, Single Nucleotide; D015203:Reproducibility of Results; D044465:White People / Q000235:genetics
chemical_list: D003181:Complement C4