Carriers of Heterozygous Loss-of-Function ACE Mutations Are at Risk for Alzheimer's Disease.

We hypothesized that subjects with heterozygous loss-of-function (LoF) mutations are at risk for Alzheimer's disease because amyloid Aβ42, a primary component of the protein aggregates that accumulate in the brains of AD patients, is cleaved by ACE (angiotensin I-converting enzyme). Thus, decreased ACE activity in the brain, either due to genetic mutation or the effects of ACE inhibitors, could be a risk factor for AD. To explore this hypothesis in the current study, existing SNP databases were analyzed for LoF mutations using four predicting tools, including PolyPhen-2, and compared with the topology of known mutations already associated with AD. The combined frequency of >400 of these LoF-damaging mutations in the general population is quite significant-up to 5%-comparable to the frequency of AD in the population > 70 y.o., which indicates that the contribution of low ACE in the development of AD could be under appreciated. Our analysis suggests several mechanisms by which ACE mutations may be associated with Alzheimer's disease. Systematic analysis of blood ACE levels in patients with all mutations is likely to have clinical significance because available sequencing data will help detect persons with increased risk of late-onset Alzheimer's disease. Patients with transport-deficient mutations (about 20% of damaging ACE mutations) may benefit from preventive or therapeutic treatment with a combination of chemical and pharmacological (e.g., centrally acting ACE inhibitors) chaperones and proteosome inhibitors to restore impaired surface ACE expression, as was shown previously by our group for another transport-deficient ACE mutation-Q1069R.