1/3 deformaties is a huge number and cant be true by any stretch of imagination. I know many people, with cousin marriages and, none of their kids are deformed, autistic or what have you. It's just seems baloony. And I know quiet a few couple they're married in far off cultures etc and some offspring of theirs is autistic.
In a country like Pakistan, people jump at cousin marriage bashing without realizing there many other factors could be involved. We dont have great track record of children immunization. There's a lot of illegal substance passed to patients from hakeem saianas, these all could play a significant role in genes deformities in people.