I've known a few people with Dawn's syndrome and the striking often abrupt and rapid tragectory is shocking.

As much as the slow decline of dementia that it's often incidents months apart before things fall apart. Is sad.

So is it in people with Downs syndrome when at 35 their often bright and cheerful life loving demeanor seems to vanish over the course of a few months.

As I understand it it's because chromosome 21 carries the genes associated with Alzheimer's so they get an extra copy, but also structure issues with the brain, increased risk of sleep apnea and other toxic conditions.

The point of these statements is to make an outlier appear as if it is part of the norm. They're bad statements to make, because at heart they are just meant to be misleading.