Alzheimer’s disease is characterized by progressive cognitive disability usually beginning with impairment of recent memories, but finally affecting all intellectual functions .
Prevalence of AD widely differs worldwide and increases with aging especially after the age of 65 years. Its etiology is unknown, but different risk factors including genetic predisposition play a role in the development of the disease. The high frequency of consanguineous marriage and the high frequency of positive family history of AD in the studied areas, especially in Al Kharga district, may support this hypothesis.
This study revealed that the total prevalence of AD in the studied areas was 1% among population aged 50 years and more, reaching 2.9% at 70–< 80 years and 9.74% at 80 years and more. Prevalence rapidly increases after the age of 70 years in this study (8.5-fold) especially among Al-Kharga population (12-fold). It was found that prevalence of AD was higher in Al Quseir city than Al Kharga (nearly 2-fold) among all age groups (50 up to < 80 years). On the other hand, the reverse was observed after the age of 80 years. This could be explained by the higher number of centenarians among population in Al Kharga than Al Quseir city as well as the high rates of heavy metal pollution in Al Quseir city which might contribute to the higher prevalence rates among younger age groups. The role of heavy metal intoxication in development of degenerative diseases among populations in this study will be published later on as a separate entity. Similarly,  reported that the prevalence rates of AD also rise exponentially with age, increasing markedly after 65 years.
Harvey and colleagues  reported that the prevalence of dementia increases exponentially between 45 and 60 years of age. Alzheimer’s disease is the most frequent diagnosis in early onset dementia followed by vascular dementia (VaD) and fronto-temporal dementia (FTD). In this study, early onset AD (50~≤ 65 years) was recorded in 7.9% of all dementia cases, and was more common among men (9.1%) than women (7%). Behavioral changes were recorded among 30% of early onset AD cases. AD of early onset (50~≤ 65 years) in this study was recorded among two brothers and one sister in one family and two brothers in another family in Al Kharga district.
Compared with other studies in Africa, Asia, the USA, and Europe, the prevalence was higher among African-American and Hispanic population living in the USA, but lower for Africans in their homelands, for reasons that remain unclear [16,17,18]. This different prevalence rates among different populations could be explained on the basis of different genetic susceptibility, different numbers of centenarians among various populations, and different methods of case ascertainment in different studies.
Prevalence of Alzheimer’s dementia was higher among females than males in all age groups. Experimental studies in mice support the higher risk of females for AD mediated by Aβ, APP, or both. The increased synaptic degeneration and altered inflammatory response may explain the increased AD risk in females .
Although  explained this gender difference in disease prevalence on the basis of the finding that women live longer than men, the finding of male to female ratio in our study (1353/932, i.e., 1.5:1) in the age group 70 years and more did not support this opinion. However, the biologic mechanisms underlying sex difference in both prevalence and severity are not fully understood . The full impact of sex as a basic biologic variable on this neurodegenerative disease remains elusive. A lot of studies suggested that gender and age are the predominant risk factors for AD . On the other hand, some studies, in the USA and other countries, assumed that age appears to consistently predict AD but gender results are inconsistent . This discrepant sex prevalence and severity could be explained by the suggestion that AD pathogenesis in women may be affected by metabolic changes induced by gonadal hormones, such as estrogen, which is known to have a protective effect on the brain. Loss of estrogen after menopause could partially lead to the deficits seen in brain metabolism in mild cognitive impairment (MCI) and AD .
About 85% of studied AD patients are of mild and moderate degrees in this study. This could be explained by the adopted epidemiological methods, door to door survey, where specialists of neurology reached patients at their homes. Using a standardized questionnaire and application of MMSE allows picking up mild and moderate cases. AD patients in these localities did not seek medical advice except in late stages or when behavioral changes are prominent. Most of the symptoms, especially memory deficits, in these localities are attributed to the aging process.
Presence of comorbidities, e.g., diabetes, hypertension, smoking, obesity, and dyslipidemia have all been found to increase the risk of AD [7, 22]. In this study, the most common reported risk factors are in order of frequency, hypertension, family history of dementia, smoking, diabetes mellitus, and epilepsy prior to AD.
Fratiglioni and colleagues  stated that, based on epidemiological studies, neuroimaging methods, and neuropathology researches, three etiological hypotheses for the development of AD have been reported with moderate or strong evidences. These include genetic, vascular (hypertension, diabetes, smoking, obesity, and high total cholesterol levels) and psychosocial risk factors. The genetic factors appear more prominent in Al Kharga district study where there was a higher rate of positive family history of AD (13.5%) which was attributed to the high rate of consanguineous marriage (> 80%) in this closed locality. On the other hand, the vascular hypothesis is more prominent in Al Quseir study in the form of higher rate of hypertension, diabetes, and smoking.
During course of dementia, 80–90% of people with dementia had evidence of neuropsychiatric symptoms (Steinberg and colleagues 2004). Non-cognitive behavioral and psychiatric disturbances such as apathy, disinhibited behavior, and sleep disturbances are usually observed in people suffering from dementia . Several studies assured that sleep disturbances were more frequent in patients with AD, and the most common sleep behavior being a tendency to confusion in early evening and wandering at night . Definite symptoms such as delusions and aberrant motor behavior (ABM) were found more common in patients with AD than in those with vascular dementia .
This study clarified that impaired self-care, memory loss, impaired social judgment, agnosia, behavioral changes, personality changes, disorientation, apraxia, and psychotic symptoms are the most frequent features of the neuropsychiatric profile of AD patients (in order of frequency). The explanation of the differences of neuropsychiatric profile of AD in this study and other studies are related to the type of methodology where most of the studies are hospital-based studies, and most of the referred AD patients to the hospital are presented with behavioral changes.
Fischer  mentioned that delusions occur in approximately one-third of AD, and AD with psychosis has an increased rate of cognitive decline. Hsieh and colleagues (2008) reported delusions in 23.1% of AD cases in nursing homes, and 28.0% of AD of outpatient department. In this study, psychotic symptoms (delusion and hallucination) were reported in about one-fourth of cases of AD (24.6%). These cases of AD having psychotic symptoms, especially positive symptoms (delusions, hallucinations, and agitation), seek early medical advice because of the stigma of these symptoms.
The study of neuropsychiatric profile of patients with dementia may have a role in differentiating different types of dementia from each other, and thus could have a role in planning treatment , particularly because such symptoms interfere with the quality of life of both patients and their care-givers.