Which gene is associated with Alzheimer's disease in individuals with trisomy 21?

Which gene is associated with Alzheimer's disease in individuals with trisomy 21?

• A. PSEN1
• B. APOE
• C. APP
• D. BACE1

Answer: (C)

The idea here is that having three copies of chromosome 21 in Down syndrome leads to overexpression of the APP gene, which sits on that chromosome. APP encodes the amyloid precursor protein, and its cleavage produces amyloid-beta peptides that aggregate into plaques. With trisomy 21, APP expression is increased, driving more production of Aβ and accelerating plaque formation, which explains why Alzheimer’s pathology is often seen earlier in these individuals. Other genes like PSEN1, BACE1, or APOE relate to Alzheimer's in other contexts, but the link between Down syndrome and AD specifically stems from extra APP on chromosome 21.

The idea here is that having three copies of chromosome 21 in Down syndrome leads to overexpression of the APP gene, which sits on that chromosome. APP encodes the amyloid precursor protein, and its cleavage produces amyloid-beta peptides that aggregate into plaques. With trisomy 21, APP expression is increased, driving more production of Aβ and accelerating plaque formation, which explains why Alzheimer’s pathology is often seen earlier in these individuals. Other genes like PSEN1, BACE1, or APOE relate to Alzheimer's in other contexts, but the link between Down syndrome and AD specifically stems from extra APP on chromosome 21.