Molecular genetic studies of systemic lupus erythematosus in Malaysia

Abstract

Systemic lupus erythematosus (SLE) is an autoimmune disease, characterized by the production of antinuclear antibody or ANA due to abnormalities of the immune system. SLE is not only a multifactorial disorder but also a polygenic and complex disease. SLE can cause renal failure, vasculitis, arthritis, thrombosis, seizures, and other neurological complications. The disease is believed to be triggered by genetic defects, environment, viral and bacterial infection. In the present study we characterised three polymorphic genes −HLA, Cytokine and PDCD1 genes −and investigated their association in a cohort of Malaysian (Malays and Chinese) SLE patients. Results from genotyping and association studies of HLA alleles showed an appreciable increase in allele frequencies of HLA-A*11, DRB1*0701, DRB1*1601-1606, DRB5*01-02 and DQB1*05, and decrease in HLA-DRB1*1101-1121, 1411, DRB1*1201-3, DRB1*1301-22, DRB3*0101, 0201, 0202, 0203, 0301 and DQB1*0301, 1304 in SLE patients compared with healthy control individuals. It was also noted that certain alleles showed race specific variation when associations were performed on individual ethnic groups. Allele frequencies of DRB1*0701 and DRB4*0101101, 0102, 0103 were significantly increased in Malay SLE patients and not in Chinese cohort when compared with healthy control individuals. On the other hand, allele frequencies of DRB1*1601-1606 and DRB5*0101, 0102, 0201, 0202, 0203 were significantly increased in Chinese SLE patients and not in Malay cohort when compared with healthy control individuals. Overall, the results obtained in this study were compatible with previous findings. HLA alleles could also be positively associated with certain clinical manifestations. Among them are oral ulcer with DQB1*02 and *05; arthritis with DQB1*0302; serositis with A*6801-02 and DRB1*1601-1606; renal disorder with DRB3*0101-0301. For Cytokine loci, IL1RC/C) and IL6 (GG/GG) are significantly increased and IL2 (GG/GG), IL4 (TTT/TCC), IL6 (GG/CG) and IL10 (ATA/GCC) are significantly decreased (p<0.05) in SLE patients compared to control individuals. Association analysis between cytokine levels and SLE revealed that the production of IL6 (-174 G/G) is significantly higher and the production of IL2 (-330 T/T and T/G) is significantly lower in patients compared to controls (p<0.01). This is probably because IL6 induce the release of acute phase protein from liver and promote removal of circulating autoantigens. While IL2 decreases might be due to the down-regulating effects of certain Th2 cytokine. The most common PDCD1 genotypes found in SLE patients were PD-1.1 (G/G), PD-1.2 (A/G), PD-1.3 (G/G), PD-1.4 (A/G), PD-1.5 (C/T) and PD-1.6 (A/G), with frequencies ranging from 40-100%. However, PD-1.3 (G/G), PD-1.4 (A/G) and PD-1.6 (A/G) were also commonly found in control individuals with frequency distributions ranging from 60-97%. Positive associations with the SLE phenotype were found for PD-1.9 (C/T), PD-1.5 (C/T) and PD-1.6 (A/A), while negative associations of PD-1.2 (G/G) (39% versus 53.4%), PD-1.3 (A/G) (0% versus 3.4%), PD-1.9 (C/C) (23.5% versus 48.3%) and PD-1.5 (C/C) (41% versus 62.4%) were observed. The contradictory result from the previous study probably reflects population differences in the haplotype structure of the PDCD1 locus. A pilot study on serum protein profile differences (detected by 2-D gel electrophoresis) between patients and control individuals was also performed in which the expression of 1-antichymotrypsin (ACT), the chain of haptoglobin (HPT), and ceruloplasmin (CPL) were found to be significantly higher or up-regulated in SLE patients. The expression of 2-HS glycoprotein (AHS), complement factor B (CFB) and the light chain of cleaved high-molecular weight kininogen (KNG) were significantly lower or down-regulated in patients with SLE compared to normal healthy controls.