Background: The fourth component of human complement (C4), an essential factor of the innate immunity, is represented as two isoforms (C4A and C4B) in the genome. Although these genes differ only in 5 nucleotides, the encoded C4A and C4B proteins are functionally different. Based on phenotypic determination, unbalanced production of C4A and C4B is associated with several diseases, such as systemic lupus erythematosus, type 1 diabetes, several autoimmune diseases, moreover with higher morbidity and mortality of myocardial infarction and increased susceptibility for bacterial infections. Despite of this major clinical relevance, only low throughput, time and labor intensive methods have been used so far for the quantification of C4A and C4B genes.

SummaryWe have demonstrated previously that carriers of a genotype called C4B*Q0 (silent allele of the C4B gene) have a substantially increased risk to suffer from myocardial infarction or stroke, and are selected out from the healthy elderly population. Because smoking carries a major risk for cardiovascular disease (CVD), it seemed worthwhile to study if these two factors interact. Study 1 involved 74 patients with angina pectoris (AP), 85 patients with recent acute myocardial infarction (AMI) and 112 survivors of a previous AMI and 382 controls from Iceland. Study 2 involved 233 patients with severe CVD and 274 controls from Hungary. Smoking habits were registered for each subject. The number of C4A and C4B genes was determined by phenotyping or genotyping. Compared to controls, C4B*Q0 carrier frequency was significantly higher at diagnosis in Icelandic smokers with AP (P = 0·005) and AMI (P = 0·0003) and Hungarian smokers with severe coronary artery disease (P = 0·023), while no such difference was observed in non-smoking subjects. Age-associated decrease in C4B*Q0 observed previously in two remote Caucasian populations was found, in the present study, to be associated strongly with smoking, and to already occur in smokers after age 50 years both in Iceland and Hungary. Our findings indicate that the C4B*Q0 genotype can be considered as a major covariate of smoking in precipitating the risk for AMI and associated deaths.

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Many recent data indicate that some alleles encoded in the central major histocompatibility complex (MHC) region (Class III) of short arm of chromosome 6 may modify the risk of cancer development. Therefore we determined 4 single nucleotide polymorphisms (SNPs) of this region (TNF‐α −308 G > A, RAGE −429 T > C, HSP70‐2 −1267 A > G, LTA 252 A > G) in genomic DNA samples from 183 Hungarian patients with colorectal cancer and 141 age matched control subjects representing the Hungarian population of the same age and gender. No significant differences were found in either SNP tested. When, however, three‐ or four‐locus haplotypes consisting of known constituents of the so‐called 8.1 ancestral haplotype (8.1AH) were considered, marked differences were observed. Frequency of TNF‐α −308A, RAGE −429C, HSP70‐2 −1267G, LTA 252G (8.1AH) haplotype was significantly (p = 0.006) more frequent (19.1%) among patients than in the controls (7.7%). Age‐ and gender‐adjusted ratio of the 8.1AH carriers vs. non‐carriers to have colorectal cancer was 2.514 (1.130–5.594). This risk was higher in ≤67 years old subjects (4.073 (1.317–12.596)) and in females (3.771 (1.302–10.927). These findings—consistent with similar recent results with ovarian cancer—indicate that carriers of the 8.1AH, encoding for an altered immune response and known to be associated with alterations of several immune functions and autoimmune diseases have an increased risk for some cancer types. These findings may contribute to better understanding how the defense mechanisms against tumors could be enhanced/strengthened. © 2007 Wiley‐Liss, Inc.

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