a global rating scale that measures cognitive symptoms of the disease. The severity of dementia was assessed with the Mini-Mental State Examination (MMSE) [45] in all patients. In addition, the Global Deterioration Scale (GDS) was also assessed in most of the patients (n = 118). Accordingly, the patients were divided into three severity groups: early or mild AD (MMSE score: 19–24, and GDS score: 3 or 4), moderate AD (MMSE score: 10–18, or GDS score: 5), and severe AD (MMSE score: ≤9, or GDS score: 6) group [16], [45], [46]. All these tests allowed us to rule out brain structural lesions as well as different causes of progressive or reversible dementias. Patients with a history of brain trauma or drug/alcohol abuse were not included. Out of 232 patients with a diagnosis of dementia that were initially recruited, 107 were excluded for having brain structural lesions, complications of a systemic disorder (e.g., renal failure, diabetes), or non-AD dementia. APOE genotyping was also performed on all participants. Like the patients, controls also underwent physical and neuropsychiatric examination, neuropsychological tests, and neuroimaging screening. All the tests in patients and controls were part of routine screenings or check-ups that took place prior to the
