I don't know what a "cousin sister" is but marrying them generation after generation will cause these genetic problems.
First cousin marriage is legal in many U.S. states and contrary to “accepted wisdom” they are by no means all southern.
For a list of states and marriage laws concerning cousins check this out:
http://marriage.about.com/cs/marriagelicenses/a/cousin.htm
Such news is never reported in Pakistan. Pakistani establishment want to keep the hatred for India alive no matter what.