Background: angiotensin-converting enzyme (ACE) gene insertion/deletion (indel) polymorphism is considered a biomarker for Alzheimer's disease (AD). However, the associations of ACE gene and protein level to AD are undetermined among Taiwanese.
Methods: this study investigated 257 Taiwanese cases with AD and 137 ethnically matched controls using ACE gene indel genotype association methods with logistic regression adjusted for other variables. Besides, 65 out of 257 AD patients, 11 with D/D genotype, 28 with I/I genotype and 26 with I/D genotype were recruited. Their plasma ACE protein levels were measured by enzyme-linked immuno-sorbent assay and compared for their corresponding ACE gene indel polymorphism.
Results: patients with ACE-I/I homozygote were less likely to be associated with AD, compared with both I/D and D/D (OR: 0.601; 95% CI: 0.372-0.969; P = 0.037), or only I/D genotype (OR: 0.584; 95% CI: 0.349-0.976; P = 0.040). There were significantly different plasma ACE protein levels among these three different genotype groups (P = 0.023). The I/I genotype group had significantly lower ACE plasma levels [114.79 ± 31.32 ng/ml (mean ± SD)], compared with D/D (164.07 ± 86.36 ng/ml; P = 0.010), but not I/D (141.45 ± 51.50 ng/ml; P = 0.064).
Conclusion: ACE-I/I homozygote corresponds to lower plasma ACE protein level and it is independently but less likely to be associated with AD. These findings signal the importance of ACE indel polymorphisms to their corresponding protein levels and to AD.