Polycystic Kidney disease

Attended a grand round on polycystic kidney disease. Left with a lot more questions than I entered with.

OK Polycystin is a part of cilia and it detects motion. If it is screwed up as it does in PKD, you get cysts.

The organs affected like Kidney, liver(Bile), colon (Feces), lung - bronchiectasis(Air) , seminal vesicles(semen) have some thing flowing in a direction.

Only in the CVS it is kind of funky in that

1)Why is it only the circle of willis is affected?  Has it got to do with the fact that blood flow can reverse its direction in COW unlike other systemic blood vessels and needs polycystin to detect the direction of blood flow, so that it can make the needed adjustments in flow so that the brain gets it's blood supply.

What about MVP and AR? Is there a role for polycystin here as well as it is the place where you want the blood to flow in one direction.

2) What is the role of estrogen in altering the function of polycystin?

3) If PKD was so bad, how did it survive evolution ? Was it a case of positive selection or Was it a case of a recent mutation that has not entirely gone through the rigor of evolution?

If it was a case of positive selection, under what conditions was it selected and what are the benefits of PKD?

More reading to do!!!