The one that I do know is that the Habsburgs post-Victoria were plagued by haemophillia, a disorder where your blood doesn't clot properly. It was passed down through Victoria through her daughters Princess Alice and Beatrice who then passed it down through their children to the royal families of Spain, Germany and Russia. Victoria's son also had it. This isn't a disorder CAUSED by inbreeding, but it is transmitted through females, usually only appearing in its full form in the males. Because there was so much intermarriage at the time, and Victoria was called the grandmother of Europe for a reason - her descendents were basically in every European royal family - it became a real issue where many royals in different countries were suffering from the disease. Because of this, haemophilia was studied more thoroughly, and we became more aware of how it was transmitted - studying family trees and who had it and who didn't. Altogether, 8 royals from her line died of their disease. Called a lot of attention to the issue and top notch physicians were obviously called upon to study it.