Amyloid Plaques and APP

APP (amyloid precursor protein) is a gene which is on the 21st chromosome so in the case of Down syndrome we have 3 copies instead of 1 or 2.

"The APP gene provides instructions for making a protein called amyloid precursor protein. This protein is found in many tissues and organs, including the brain and spinal cord (central nervous system). Little is known about the function of amyloid precursor protein. Researchers speculate that it may bind to other proteins on the surface of cells or help cells attach to one another. Amyloid precursor protein is cut by enzymes to create smaller fragments (peptides), some of which are released outside the cell." (1)

For a great visual of how the APP is cut watch this video:
{The screen is cut off for some reason, here is the link to youtube}





Amyloid precursor protein is cut by enzymes to create smaller fragments (peptides), some of which are released outside the cell. Two of these fragments are called soluble amyloid precursor protein (sAPP) and amyloid beta peptide. Recent evidence suggests that sAPP has growth-promoting properties and may play a role in the formation of nerve cells (neurons) in the brain both before and after birth. Other functions of sAPP and amyloid beta peptide are under investigation.
As shown in the animation, beta secretase enzyme cuts the amyloid precursor protein in the wrong spot so that when the gamma secretase enzyme makes its usual cut the protein is now insoluble and clumps together to form plaques. The plaques continue to accumulate eventually clogging the brain and destroying neurons. No one knows exactly when amyloid plaques develop in Down syndrome just that APP gene is at a dose of 1.5 times that of normal.
"When they reach 30 or 40 years of age, individuals with Down syndrome develop amyloid plaques in their brains identical to those found in the brains of Alzheimer's patients, leading to similar symptoms such as loss of nerve cells and dementia." (1)
1) Read more at Suite101: Alzheimer's Disease Linked to Down Syndrome: Amyloid Protein Causes Damage to Cells in Both Conditions http://www.suite101.com/content/alzheimers-disease-linked-to-down-syndrome-a191444#ixzz1C4Fs68os