Genotypic and phenotypic description of late-onset Alzheimer’s disease and early onset familial Alzheimer’s: Review

Abstract

Dementia is known as the loss of multiple areas of cognitive function with respect to a premorbid condition, involving a significant deterioration in functionality. The most common subtype is Alzheimer’s disease, which is defined as a neurodegenerative disorder that causes a progressive deterioration in memory and other mental capacities due to volume loss in temporal lobes, especially in mesial aspects, such as the hippocampus and the entorhinal cortex. Approximately 5% of patients affected by this disease have a hereditary form, with an early onset (before 65 years) or a late onset (after 65 years). Early onset Alzheimer’s disease has a genetic autosomal dominant inheritance pattern, which can be caused by mutations in the gene encoding for the amyloid precursor protein, presenilin-1, or presenilin-2. In the cases of late onset Alzheimer’s disease, there is a complex genetic influence, with multiple susceptibility factors, where the ApoE4 allele is the main and most recognized factor. Alzheimer’s disease is a heterogeneous dementia, both in genotype and phenotype, varying in intensity and symptoms, age of onset, and severity of the disease, depending on the different mutations that a patient may have and the interactions with environmental factors.