Well, the actual scientific explanation for a congenital condition is that it's just a mistake - a copying error in the DNA, a botched step in the process of pregnancy. My own illnesses fall into this category. It's nobody's fault that I'm ill; it's not the wages of sin, or the sign of God's anger; and crucially, there's no need to exclude me from society - in fact, I ought to be included. The gods have messed up, but they also care about the people who're affected by it.