Well........that's what happens when cousins marry.
Actually the problems with cousins marrying is overblown. All that does is intensify the genetic traits, which means if there are good genetic traits they will most likely be passed on. The only problem comes in when there are bad genetic traits that get intensified.
So if there is a tendency towards insanity, retardation, or other negative genetic traits, then such a marriage would indeed carry a higher possibility of being problematic. However if both carry positive genes such as high intelligence, good physical build, high metabolism and energy, soundness of mind and emotional stability, then those traits would be strengthened.
Of course too much close marriages will eventually lead to problems, but a little of that in good gene pools is actually helpful, as anyone that breeds dogs, horses, or cows can tell you.
Several of our past presidents married their first cousins. Once it gets to second cousins, or first cousins twice removed the danger is non-existent. However some states actually have laws against first cousins marrying. Of course some states have laws against high capacity magazines also.