CONTEMPO UPDATES LINKING EVIDENCE AND EXPERIENCE Alzheimer Disease

Incidence, Prevalence, and Economic Impact Alzheimer disease accounts for 60% to 70% of cases of progressive cognitive impairment in elderly patients. The total prevalence of AD in the United States is estimated at 2.3 million (range, 1.094.8 million). The prevalence of AD doubles every 5 years after the age of 60 increasing from a prevalence of 1% among those 60to 64-years-old to up to 40% of those aged 85 years and older. The disease is more common among women than men by a ratio of 1.2 to 1.5. The number of new cases per year is estimated at 360000 equating to 980 new cases per day or 40 new cases every hour. The population of patients with AD will nearly quadruple in the next 50 years if the current trend continues. The direct costs for the care of patients in 1991 were calculated at US $20.6 billion and the total cost was calculated to be $76.3 billion. Most direct costs of care for patients with AD are absorbed by the expense of nursing home care, approximately $47000 per patient per year. Several risk factors for AD have been identified in epidemiologic studies in addition to age and female sex. The most potent risk factor is the presence of the apolipoprotein 4 (APOE 4) allele. Of its 3 forms— 2, 3, and 4—only the 4 allele increases the likelihood of developing AD. The lifetime risk of AD for an individual without the 4 allele is approximately 9%; the lifetime risk of AD for an individual carrying at least 1 4 allele is 29%. While representing a substantial risk of AD, the 4 genotype is not sufficiently specific or sensitive for the diagnosis of AD to allow its use as a diagnostic test. Moreover, the 4 allele appears to increase the risk of AD more in white and Asian populations than in black and Hispanic populations. Other risk factors implicated in a variety of studies include head injury, low serum levels of folate and vitamin B12, elevated plasma and total homocysteine levels, family history of AD or dementia, fewer years of formal education, lower income, and lower occupational status. Conversely, higher levels of education, moderate levels of daily wine consumption, and higher levels of fish in the diet have been associated with a lower risk for AD. Differences in the prevalence of AD among population groups worldwide suggest as yet undisclosed genetic or environmental effects on the prevalence of AD.