The number of savants found in autistic populations is about 1 in 2000, and those tend to have less than useful "specializations". There are actual specific types of retardation where the afflicted person has a very positive disposition, as well as significantly diminished mental capacities. There are a number of different factors that contribute to retardation, inbreeding is indeed one of them. I would pause before calling those who are socially inept "retarded".