I'm more suspicious of things like pesticides or other environmental chemicals playing a role in people developing the condition. I grew up in an agricultural area (mostly fruit orchards) and we had a well. We now live in an agricultural area (corn, soybeans, sunflowers, and grain) and have a well. Mine, my siblings', and my child's exposure to pesticides is almost certainly higher than that of the average American living away from agriculture and drinking water from sources away from farmland.