Association Between Polymorphisms Of The Genes Whose Products Interact With SARS-CoV N Protein And Susceptibility To SARS-CoV

Severe acute respiratory syndrome (SARS) is a highly transmissible human infectious disease with respiratory symptoms and is caused by a newly identified coronavirus (CoV), SARS-CoV. The rapid transmission, high infectivity and unpredictable clinical progression make SARS a potential global threat, but its pathogenesis is still not fully clarified. Most infectious diseases are multifactorial and polygenic events with microbial, environmental and genetic components, genetic variation has been regarded as an important factor in determining susceptibility to diseases. Clinical investigations about SARS and several association studies have shown that individual susceptibility to infection with SARS-CoV seems to be variable, i.e. for seropositive subjects for SARS-CoV may develop SARS or only have mildly symptomatic infections which cannot reach the criteria of SARS cases, and approximately 20% of SARS patients develop progressive pulmonary infiltrates and respiratory failure. Thus, it is conceivable that genetic variation may be an additional causation in individual's susceptibility to SARS or disease severity after SARS-CoV infection. In order to investigate the important roles of genetic factor, Interaction of SARS-CoV with host was investigated. It was found that the nucleocapsid protein one of the most abundant structure protein, of SARS-CoV, interact with Cytochrome P450 family F peptide 3 (CYP4F3), HS glycoprotein G (AHSG) and Mannan-binding lectin-associated serine protease-2 (MASP2) in human cells. In the present paper, we performed case- control study to assess whether there is an association between the polymorphisms of the above mentioned genes and susceptibility to SARS-CoV infection in Chinese populations. The results may contribute to the further understanding of pathogenesis of SARS-CoV infection, and may lead to the improved prevention and treatment of the disease.In the present study, we screened for polymorphisms of three candidate genes in all exons, 5'and 3'flanking regions and untranslated regions. Linkage disequilibrium (LD) calculation was performed using Haploview software, the tag SNP and other potential functional polymorphisms were chosen for association studies. The subjects from several populations were included for case-control genetic association studies: Beijing non-HCW (non health care work) population were recruited from Xiaotangshan Hospital and 307 Hospital (272 cases, 424 controls ); Guangzhou non-HCW population were from the Eighth People's Hospital of Guangzhou and GuangZhou Army General Hospital (67 cases, 192 controls); Guangzhou HCW population consisted of health care workers of the Second Hospital of Zhongshan University (40 cases, 122 controls). All non-HCW patients were from community of Han Chinese, non-HCW controls were recruited from the corresponding general physical examination people with no other symptoms. Genotyping was completed using the SNPstream Ultra High Throughput genotyping platform. Genotype and allele distributions between patient categories and control subjects were compared by using the logistic regression analysis; ORs and 95% CI were calculated to express relative risks. These analyses were performed using SPSS 13.0 software.Major results: (1) The SNP genotyping and genetic analysis pipeline were established in our laboratory. (2) Genotype and allele frequencies of -799A/T, rs4917 and rs1071592 variants were found significantly different between non-HCW cases and controls. The presence of the AHSG -799T allele (-799A/T or T/T genotype) [OR, 2.44 (95% CI, 1.32-4.57); P = 0.005] or the rs4917T allele (rs4917C/T or T/T genotype) [OR, 1.59 (95% CI, 1.21-2.08); P = 0.001] was significantly associated with increased susceptibility to SARS-CoV infection, compared with the -799A/Aor -863C/C genotype respectively. AHSG is a multifunctional acute negative reactant in the inflammatory phase. AHSG suppress the production of tissue necrotizing factor–α(TNF-α) and other inflammatory factor. Gel shift assay showed that the -799T DNA fragment had a greater affinity with transcription factor AP-1 than the -799A. A reporter gene assay showed that the -799A allele had significantly higher promoter activity compared with the -799T allele. In concert with the findings, serum fetuin-A levels in SARS cases were found significantly lower than in the controls. In conclusion, the presence of the -799T allele appears to be associated with an increased risk of SARS-CoV infection. (3) Genotype and allele frequencies of -903A/G, -815A/G, -140C/T, rs4646519 polymorphisms and haplotype AGT showed significant difference between non-HCW cases and controls. The presence of the CYP4F3 -903AA genotype [OR, 1.41 (95% CI, 1.05-1.90); P = 0.022], the -815G allele (-815A/G or G/G genotype) [OR, 1.81 (95% CI, 1.36-2.44); P = 0.0001] or -140T allele (-140C/T or T/T genotype) [OR, 2.44 (95% CI, 1.78-3.42); P = 0.0001] was significantly associated with increased susceptibility to SARS-CoV infection, compared with the -903G/G, A/G, -815A/A or -140C/C genotype respectively. Haplotype analysis also revealed that haplotype ATG (in the order of -903A→G, -815A→G and -140C→T) had a significantly increased susceptibility to SARS-CoV infection, compared with the other haplotypes. CYP4F3 catalyze LTB4, a potent chemotactic and chemokinetic agent which plays an important role as a mediator of inflammation, into biologically less active 20-OH-LTB4 by theω-oxidation pathway. Higher level of serum CYP4F3 would lead to lower serum level of LTB4, and less effective inflammatory reaction in the host for defenses. Reporter gene assay showed that haplotype AGT had highest promoter activity among the haplotypes. Promoter analysis of the CYP4F3 gene demonstrated that the -174/-90 region was important for its promoter activity. Our results showed that the -140T allele had significantly higher promoter activity compared with the -140C allele. The presence of the -140T allele or AGT haplotype has higher promoter activity, lower serum level of LTB4, and appears to be associated with an increased risk of SARS-CoV infection. Gene-gene interaction of AHSG and CYP4F3 polymorphisms significantly increased the risk of SARS-CoV infection. (4) No significant association was found between MASP2 alleles or genotypes analyzed and the susceptibility to SARS-CoV. Our data do not seem to suggest a role for MASP2 polymorphisms in SARS susceptibility.