Microsatellite DNA Polymorphism of Human Adrenomedullin Gene in Normotensive Subjects and Patients with Essential Hypertension
Objective: Adrenomedullin (AM) is a hypotensive peptide widely produced in the cardiovascular organs and tissues such as the heart, kidney and the vascular cells. We investigated the association between DNA variations in AM gene and the predisposition to essential hypertension. Methods: We have cloned and sequenced the genomic DNA encoding human AM gene, and determined that the gene is located in the short arm of chromosome 11. The 3’-end of the gene is flanked by the microsatellite marker of CA repeats. Genomic DNA was obtained from the peripheral leukocytes of healthy normotensive subjects (NT; 179 men and 100 women, 57±6 years) aging 50 years or more and patients with essential hypertension (EH; 162 men and 98 women, 53±11 years) who had developed hypertension before the age of 50 years. The genomic DNA was subject to PCR using a fluorescence-labeled primer, and the number of CA repeats were determined by poly-acrylamide gel electrophoresis. Plasma AM concentration was measured by RIA and compared with respect to the number of CA repeats adjacent to the AM gene. Results: The averaged blood pressure was 117±13/73±9 mmHg in NT and 170±23/104±12 mmHg in EH when the patients were not treated. In Japanese, there existed four types of allelles with different CA-repeat number; 11, 13, 14 and 19. The frequencies of these alleles were 11: 28.7%, 13: 33.6%, 14: 34.7% and 19: 3.0% in NT and 11: 30.5%, 13: 28.4%, 14:34.3% and 19: 6.8% in EH. Thus, the frequency of 19 CA repeat allele was higher in EH than in NT (χ2=10.25, p<0.02). Namely, 13.5% of EH carried the 19-repeat allele, while the frequency was 6.1% in NT (χ2=8.43, p<0.004). In NT, plasma concentrations of AM in 21 homozygotes of 11-repeat allele, 27 homozygotes of 13-repeat allele, 30 homozygotes of 14-repeat allele and 17 heterozygotes carrying 19-repeat allele were 7.5±1.0, 7.0±1.3, 7.2±1.3 and 7.3±1.7 fmol/ml, respectively, and the values were not significantly different between the genotypes. Conclusion: Microsatellite DNA polymorphism of AM gene may be associated with the genetic predisposition to EH, although the gene expression is not likely to be affected by the genotypes.