Final answer:
Alzheimer's disease is a degenerative brain disorder marked by amyloid plaques and neurofibrillary tangles, leading to memory loss and cognitive decline. It has both a rare early-onset form linked to specific genetic mutations and a more common late-onset form with a genetic component such as the APOE E4 gene variant.
Step-by-step explanation:
Alzheimer's disease (AD) is a degenerative brain disorder characterized by a decline in memory, changes in cognitive functioning, and behavioral alterations. At the microscopic level, the brains of individuals with Alzheimer's show distinctive changes including the accumulation of amyloid plaques and neurofibrillary tangles. These pathological hallmarks are associated with synaptic loss, neuronal death, particularly in the hippocampus—responsible for memory formation—and a reduction in overall brain volume. The disease was first reported by Alois Alzheimer in 1911 and is often associated with dementia symptoms such as disruptive memory loss, confusion, and personality changes.
Alzheimer's can be either early-onset, which is less common and often linked to genetic mutations, or the more prevalent late-onset form, which also has a genetic component. For instance, the apolipoprotein E (APOE) gene, especially its E4 variant, increases the risk of developing the disease. Understanding the genetic factors and the pathology of Alzheimer's is crucial for advancing treatments and potential preventatives for this debilitating condition.