Apolipoprotein E genotype and cerebrovascular alterations can influence conversion to dementia in patients with mild cognitive impairment

The presence of apolipoprotein E (APOE) e4 allele is the only recognized genetic risk factor for the sporadic form of Alzheimer's disease. The aim of this study was to investigate the relationship between APOE genotype and the functional and anatomic status of cerebral vessels in patients with mild cognitive impairment (MCI). Moreover, we explored whether the possible correlation between APOE genotype and cerebrovascular parameters influences the risk of conversion from MCI to dementia. 75 MCI patients underwent a complete neuropsychological battery at baseline and after 24 months to evaluate the possible conversion to dementia. Ultrasound assessment of neck and intracranial vessels was performed to assess common carotid artery intima-media thickness (IMT), plaque index, and cerebrovascular reactivity (breath-holding index, BHI). APOE genotype was determined to classify patients as carriers (APOE e4+) and non-carriers (APOE e4-). Pathologic values of BHI and IMT were significantly more common in e4 carriers than in non-carriers [OR 6.603 (95% CI: 1.678-25.997), p < 0.05 and OR 5.195 (95% CI 1.319-20.464), p < 0.05; logistic regression adjusted model]. The risk of conversion to dementia was significantly higher in APOE e4+ patients than in APOE e4- ones (OR: 6.818; 95% CI:1.894-24.545, p = 0.003). A path-analysis model showed that APOE genotype influences the progression to dementia directly and indirectly by increasing the risk of pathologic values of IMT or BHI. Our data, besides confirming an increased susceptibility of MCI patients with APOE e4 to develop dementia, show an association between functional and anatomic impairment of the cerebral vessels and APOE e4+ genotype.