Genetic Studies of Alzheimer's Disease

Sammanfattning: Patients with Alzheimer's disease (AD) often have a family history of the disease, implicating genetics as a major risk factor. Three genes are currently known to cause familial early-onset AD (<65 years): the amyloid precursor protein (APP) and the presenilins (PSEN1 and PSEN2). For the much more common late-onset disease (>65 years), only the APOE gene has repeatedly been associated to AD, where the ?4 allele increases disease risk and decreases age at onset. As APOE ?4 only explains part of the total estimated disease risk, more genes are expected to contribute to AD.This thesis has focused on the study of genetic risk factors involved in AD. In the first study, we conducted a linkage analysis of six chromosomes previously implicated in AD in a collection of affected relative pairs from Sweden, the UK and the USA. An earlier described linkage peak on chromosome 10q21 could not be replicated in the current sample, while significant linkage was demonstrated to chromosome 19q13 where the APOE gene is located. The linkage to 19q13 was further analyzed in the second study, demonstrating no significant evidence of genes other than APOE contributing to this peak. In the third study, the prevalence of APP duplications, a recently reported cause of early-onset AD, was investigated. No APP duplications were identified in 141 Swedish and Finnish early-onset AD patients, implying that this is not a common disease mechanism in the Scandinavian population. In the fourth study, genes with altered mRNA levels in the brain of a transgenic AD mouse model (tgAPP-ArcSwe) were identified using microarray analysis. Differentially expressed genes were further analyzed in AD brain. Two genes from the Wnt signaling pathway, TCF7L2 and MYC, had significantly increased mRNA levels in both transgenic mice and in AD brains, implicating cell differentiation and possibly neurogenesis in AD.