Background: The serum-angiotensin I converting enzyme (s-ACE) activity is influenced by a genetic insertion/deletion (I/D) polymorphism in the ACE gene, and the resulting large interindividual variation in s-ACE limits the use of normal reference intervals in the evaluation of sarcoidosis. In this study, we developed a new method for genotyping the I/D polymorphism in ACE and established genotype-specific reference intervals in order to improve the diagnostic accuracy and the value for treatment of sarcoidosis.
Methods: The new genotyping assay is based on high-resolution melting (HRM) using LCGreen + and was used to genotype 400 healthy Danish individuals. The assay was compared to a real-time polymerase chain reaction (RT-PCR) assay in a validation set of 86 samples. Enzyme activity in serum was measured using the Infinity™ ACE Liquid Stable Reagent from Thermo adapted for the ABX Pentra analyzer.
Results: There was full concordance between genotyping assays. The three genotypes II, ID and DD were present with a frequency of 0.23, 0.51 and 0.26. The distribution of s-ACE values in the total population was non-Gaussian (non-parametric 95% reference interval 12.0-60.0 U/L). The median activities of the genotypes differed significantly (P<0.0001). Ninety-five per cent non-parametric reference intervals for the subpopulations were determined to 6.3-38.5, 14.0-56.0 and 23.3-71.2 U/L for II, ID and DD, respectively.
Conclusion: We have developed a simple and robust method for ACE genotyping and determined genotype-specific reference intervals for s-ACE concentrations in the Danish population. The new reference intervals may increase the value of s-ACE measurements.
Keywords: Angiotensin I converting enzyme; I/D polymorphism; genotype-specific reference intervals; high-resolution melting; molecular diagnostics; peptidyl-dipeptidase; sarcoidosis.
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