Alzheimer disease

Disease class: Tauopathies

AD is the most common cause of dementia.

Pathophysiology

This disease has been poorly understood throughout medical history despite a large amount of research. There is an accumulation of tau protein. The protein "beta-amyloid" misfolds and accumulates in toxic plaques which can kill neurons. On brain scans, gross atrophy tends to appear first in the temporal lobes and parietal lobes. The hippocampus (in the medial temporal lobe) is usually one of the first structures affected. The hippocampus plays a key role in transferring short-term memories into long-term memory, and this is why anterograde amnesia is usually an early symptom.

Patients with Down's syndrome (tri-somy 21) have an 3rd copy of chromosome 21. Chromosome 21 contains the gene which produces beta-amyloid, therefore trisomy 21 patients have an unusually high amount of beta-amyloid in their brain. These patients have an extremely high rate of Alzheimer's disease, with an early onset.

Symptoms

These patients usually notice significant forgetfulness and disorientation as their first symptoms. Extrapyramidal symptoms usually develop late in the course of the disease.