Factors affecting the age of onset and rate of progression of Alzheimer's disease

Objectives-To assess the role of cerebrovascular disease, sex, education, occupation, year of birth, leukoaraiosis, congophilic angiopathy, family history, and other demographic factors on the reported age of onset and rate of progression of Alzheimer's disease. Methods-Analysis of data from the University of Western Ontario Dementia Study, a prospective longitudinal study of dementia patients with clinical and 6 monthly psychometric follow up to postmortem based in a university memory disorders clinic with secondary and tertiary referrals. There were 172 patients with dementia. The main outcome measures were the reported age of onset of cognitive decline as described by the family (available in 168) and rate of progression as measured during the linear phase of the extended scale for dementia, which could be calculated in 66. The cases subdivided into 49 cases of definite Alzheimer's disease without infarcts, 25 cases of otherwise definite Alzheimer's disease with infarcts, 79 cases of probable Alzheimer's disease without infarcts, and 19 such cases with infarcts. Results-The age of onset was not influenced by the rate of progression, the presence of cerebral infarcts, or congophilic angiopathy. Educational level, occupational level, sex, family history, year of birth, reported age of onset, severity at entry, an ischaemic score, and the presence of leukoariosis, affected neither age of onset nor the rate of progression. An earlier year of birth had a major effect and higher education had a minor effect on earlier age of onset. The earlier the year of birth, the lower the educational level and the greater the accrual of cerebral infarcts. Conclusions-Contrary to series without pathological verification, age of onset in this study was not affected by occupation. Education had a modest effect on earlier reported onset, probably reflecting earlier recognition. As birth year has a strong effect on educational level and the occurrence of cerebral infarcts, this must be taken into account when analysing for risk factors for Alzheimer's disease.