What fibrous protein is linked to an increased risk of Alzheimer's in individuals with trisomy 21?

The fibrous protein that is linked to an increased risk of Alzheimer's disease in individuals with trisomy 21, also known as Down syndrome, is the amyloid precursor protein (APP). This connection arises because individuals with trisomy 21 have an extra copy of chromosome 21, which contains the gene for APP.

Increased levels of APP can lead to the overproduction of amyloid-beta peptides, which are the primary components of amyloid plaques found in the brains of Alzheimer's patients. The accumulation of these plaques is a hallmark of Alzheimer's disease and is thought to contribute significantly to neurodegeneration and cognitive impairment associated with the condition. Thus, the presence of the extra APP due to trisomy 21 is a crucial factor in understanding the heightened risk for Alzheimer's in this population.

The other options listed (ghrelin, leptin, and beta-endorphin) are not directly related to the pathological mechanisms of Alzheimer's disease in the context of trisomy 21. Ghrelin and leptin are hormones involved in appetite regulation and metabolism, while beta-endorphin, a neuropeptide, is related to pain relief and stress response, and none of them have a direct correlation with the amyloid pathology associated with Alzheimer's disease.