Genetic and Epigenetic Architecture of Alzheimer’s Dementia

Down syndrome, Alzheimer disease, and cerebral amyloid angiopathy: The complex triangle of brain amyloidosis

Down syndrome (DS) is the main genetic cause of intellectual disability worldwide. The overexpression of the Amyloid Precursor Protein, present in chromosome 21, leads to β-amyloid deposition that results in Alzheimer disease (AD) and, in most cases, also to cerebral amyloid angiopathy (CAA) neuropathology. People with DS invariably develop the neuropathological hallmarks of AD at the age of 40, and they are at an ultra high risk for suffering AD-related cognitive impairment thereafter. In the general population, cerebrovascular disease is a significant contributor to AD-related cognitive impairment, while in DS remains understudied. This review describes the current knowledge on cerebrovascular disease in DS and reviews the potential biomarkers that could be useful in the future studies, focusing on CAA. We also discuss available evidence on sporadic AD or other genetically determined forms of AD. We highlight the urgent need of large biomarker-characterized cohorts, including neuropathological correlations, to study the exact contribution of CAA and related vascular factors that play a role in cognition and occur with aging, their characterization and interrelationships. DS represents a unique context in which to perform these studies as this population is relatively protected from some conventional vascular risk factors and they develop significant CAA, DS represents a particular atheroma-free model to study AD-related vascular pathologies. Only deepening on these underlying mechanisms, new preventive and therapeutic strategies could be designed to improve the quality of life of this population and their caregivers and lead to new avenues of treatment also in the general AD population.

Novel presenilin 1 mutation (p.Thr-Pro116-117Ser-Thr) in a Spanish family with early-onset Alzheimer's disease

Presenilin 1 (PSEN1) is a γ-secretase component, which is in charge of the amyloid precursor protein (APP) cleavage. APP is believed to play a central role in the pathogenesis of Alzheimer's disease (AD). PSEN1 mutations are the most important causes of familial AD, being related to the earlier onset and rapid progression of the disease. Presenilins and APP mutations represent an extraordinary opportunity to study the pathophysiology of AD. We describe the clinical and genetic study of a 37-year-old male patient with a novel mutation in PSEN1 (p.Thr-Pro116-117Ser-Thr). We have studied the pedigree of his family with a further 9 members affected, all of them with onset in their 30s. We have also described the clinical data and results of brain biopsies in 2 of them. DNA sequencing of a tissue sample from an uncle of the patient, who died of AD in the 80s, showed the same mutation as in the patient. These data and predictive analysis indicate the pathogenicity of the mutation.