APOE (the ALZ gene) and a protein called reelin and the receptor route.

https://www.cnn.com/2023/05/15/health/alzheim...index.html

She carried two copies of a change in her APOE3 gene that was nicknamed the Christchurch mutation. It seems to have decreased the activity of the APOE3 protein. Like reelin, APOE is a signaling molecule that is known to play a role in shaping a person’s risk for Alzheimer’s.

And it turns out that there is a link between these two cases: The receptors on cells for reelin are the same receptors for APOE.