Descriptive and analytic epidemiology of Alzheimer’s disease

Summary

Alzheimer’s disease represents the most frequent cause of dementia in old age. Available prevalence ratios (cases per 100 population aged 65 and over) range between 0.6 in China (Shen et al., 1987), and 5.8 in Scotland (Broe et al., 1976). This variability can be influenced by different definitions of the disease under study and different case ascertainment procedures adopted. All the studies consistently showed an exponential increase of the prevalence ratios with age, and, in many studies, the age-specific prevalence ratios were consistently higher in women than in men. In analogy with the prevalence pattern, the incidence rates for Alzheimer’s disease raise exponentially with age and are higher in females. The rate can be estimated around 0.01 per 1000 in the age 40–60-year group and it raises to 10 per 1000 in subjects aged 75 years and over (Mas et al., 1987).

As far as risk factors for Alzheimer’s disease are concerned, our knowledges principally base on findings derived from case-control studies. A family history of dementia and a previous head trauma were found to be associated with Alzheimer’s disease in case-control studies. Indications of the role of genetic factors in the etiology of Alzheimer’s disease also derived from genetic studies, which demonstrated a genetic defect localized on chromosome 21 in some families with an high incidence of Alzheimer’s disease. Other factors found associated with Alzheimer’s disease in case-control studies are smoking, and exposure to aluminum. The comprehension of these and other hypothesized risk factors need further investigations.