It’s been suggested before that Down syndrome and Alzheimer's are connected. Similarly, there has been evidence for connections between diabetes and Alzheimer’s, and cardiovascular disease and Alzheimer’s. Now new evidence shows that all of these share a common disease mechanism. According to animal and cell-culture studies, it seems all Alzheimer's disease patients harbor some cells with three copies of chromosome 21, known as trisomy 21, instead of the usual two. Trisomy 21 is characteristic of all the cells in people with Down syndrome. By age 30 to 40, all people with Down syndrome develop the same brain pathology seen in Alzheimer's. It now appears that amyloid protein is interfering with the microtubule transport system inside cells, essentially creating holes in the roads that move everything, including chromosomes, around inside the cells. Incorrect transportation of chromosomes when cells divide produces new cells with the wrong number of chromosomes and an abnormal assortment of genes. The beta amyloid gene is on chromosome 21; thus, having three copies produces extra beta amyloid. The damage to the microtubule network also interferes with the receptor needed to pull low-density lipoprotein (LDL — the ‘bad’ cholesterol) out of circulation, thus (probably) allowing bad cholesterol to build up (note that the ‘Alzheimer’s gene’ governs the low-density lipoprotein receptor). It is also likely that insulin receptors are unable to function properly, leading to diabetes.
Reference:
[1460]
(2010). Alzheimer A{beta} Peptide Induces Chromosome Mis-Segregation and Aneuploidy, Including Trisomy 21: Requirement for Tau and APP.
Mol. Biol. Cell. 21(4), 511 - 520.
[1464]
(2010). LDLR Expression and Localization Are Altered in Mouse and Human Cell Culture Models of Alzheimer's Disease.
PLoS ONE. 5(1), e8556 - e8556.
