Genetic complexity of Alzheimer's disease: successes and challenges.

About 1% of Alzheimer's Disease (AD) cases have an early-onset autosomal dominant familial form of the disease, genetic analyses of which have found three causal genes: amyloid β-protein precursor (AβPP), presenilin 1 (PS1) and presenilin 2 (PS2). The APOE gene is the only robustly replicated risk factor for the common form of AD with onset after 65 years of age. In at least half of the AD cases, there is no known cause of the disease. Here we provide an overview on known AD-linked genes and discuss the strategies of searching for novel AD genetic risk factors.