Amyloid β-Protein

Amyloid beta (Aβ or Abeta) is a peptide of 39–43 amino acids that appear to be the main constituent of amyloid plaques in the brains of Alzheimer's disease patients.

The protein fragment, Aβ, that is broken down in a normal brain, begins to accumulate into tiny clusters known as plaques. These plaques exist between nerve cells in the brain and have the effect of destroying nerve tissue. It has been known for some time that the higher the levels of beta amyloid in the brain the greater the level of brain impairment.

Aβ interacts with the signalling pathways that regulate the phosphorylation of the microtubule-associated protein tau. Hyperphosphorylation of tau disrupts its normal function in regulating axonal transport and leads to the accumulation of neurofibrillary tangles and toxic species of soluble tau.

Alzheimer's disease and Down syndrome relation is not fully elucidated. However, it shouldn't be just a coincidence that the gene for the amyloid beta precursor APP is located on chromosome 21, and patients with trisomy 21 - better known as Down syndrome - who thus have an extra gene copy almost universally exhibit AD-like disorders by 40 years of age.

More to be learned from genome sequencing studies in the post genomics era.

Relevant:
http://www.ahaf.org/alzheimers/
http://www.emergentuniverse.or...
http://www.dnalc.org/view/798-...
http://www.physorg.com/tags/be...
http://www.healthcentral.com/a...