Great Debate! I'm glad to finally find a sermon on this site that includes the right side of this argument. Listen very carefully to both sides and don't go with your knee-jerk reaction. Actually think about the long-reaching messages of the Bible and the not specific verses that are so easy to take wildly out of context.
The rate among identical twins should be 100%? When one identical twin has multiple sclerosis, their twin has 1 in 4 chance of having it, too. NOT 100%. "Just" 1 in 4, but still a lot higher than if they were just parent/children, or not relatives at all. Not all genetic conditions are 100% similar among identical twins.