Let's not jump to conclusions. That guardian article is about a pre-print study that used frozen brain samples from a single tissue bank, and RNA sequencing was done on a single machine.

There's a lot of controversy around this[1], because contamination is possible and it's known that the blood brain barrier weakens with age. The sample are all from older individuals.

[1] https://www.news-medical.net/health/Is-there-a-brain-microbi...