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- angiotensin converting enzyme
- Asian subjects
- polymerase chain reaction
- systemic lupus erythematosus
The ACE insertion/deletion (I/D) polymorphism has been inconsistently reported to be associated with systemic lupus erythematosus (SLE).1–3 We proposed the hypothesis that the genetic sequence variation of ACE may not cause SLE, but may participate in disease progression. Among the 13 polymorphisms of the ACE gene recently reported, a polymorphism in exon 17, ACE 2350 G>A, has the most significant effect on plasma ACE concentrations4 and has been shown to be associated with essential hypertension.5 We carried out a retrospective, case-control study of the two polymorphisms for putative associations with SLE and allied phenotypes among a homogeneous Asian population.
METHODS AND RESULTS
We investigated a sample group of 39 patients with SLE (mean (SD) age 33 (10) years; nine men) and 79 healthy control Pakistani subjects from the Aga Khan University Hospital, Karachi, matched for age (35 (9) years) and sex (20 men). Informed consent was taken from all participants and international guidelines for sample collection were followed.6 All patients fulfilled the American College of Rheumatology criteria for SLE.7 We used the Systemic Lupus Activity Measure (SLAM)8 score at diagnosis as an indicator of disease severity; a SLAM score ⩾20 indicating severe SLE and ⩽10, mild disease. Our patients predominantly had moderate disease activity (SLAM 11–19) at diagnosis and only three patients had mild SLE.
Genotyping for ACE I/D and 2350 G>A polymorphisms was done as previously described.5,6 Table 1 shows that the differences in the distributions of the six genotypes were not significant for either of the ACE polymorphisms, as assessed by χ2 analyses on 3×2 tables. The groups were in Hardy-Weinberg equilibrium for both markers as shown by the DA statistics.9 The frequency of the 2350A allele increased from 17% in mild SLE to 28% in moderate disease to 32% in severe SLE.
Haplotype analysis and linkage disequilibrium (LD) statistics obtained using Powermarker version 2.010 showed that the D and 2350A alleles were in strong linkage disequilibrium (LD) (D = −0.23, D′ = 0.72, χ2 = 64.4, p<0.001). The extent of LD was more in severe SLE (D′ = −0.52, χ2 = 5.04, p = 0.025) than in mild to moderate disease (D′ = −0.26, χ2 = 1.42, p = 0.23). The DA haplotype was more frequent in severe SLE than in mild to moderate disease (odds ratio = 1.43, 95% confidence interval = 0.38 to 5.35, χ2 = 0.36, 1 df, p = 0.55).
SLE is present in an aggressive form (moderate to severe disease) in the Pakistani population. Although assessing SLE severity is not simple, as various factors such as response to treatment and type of organ affected and organ damage determine the nature of the disease, we used the SLAM index at diagnosis as an indicator of disease severity. All our patients presented within 6 months of symptom onset, which made SLAM at diagnosis a comparable index of SLE severity.
The ACE gene does not appear play a part in the development of SLE as shown by the lack of association of the ACE I/D and G>A polymorphisms, which is consistent with previous findings for ACE I/D.2 Though the frequency of the 2350A allele was similar in both groups, its distribution was skewed towards severe SLE (SLAM >20). The D and the 2350A alleles were in strong LD and the predominant transmission of the DA haplotype in severe SLE indicated its association with severe SLE. These results support the involvement of ACE polymorphisms with increasing disease severity of SLE.
We are grateful to our patients for their participation and to Drs Philippe Frossard, Ata Khan, and Adil Abbas for help with patient recruitment.