Complex sentence: FXIIID, while generally rare, Iran has the highest global incidence of disorder with 473 cases; the city of Khash has the highest incidence in Iran, as it is in Sistan and Balochistan provinces with high rate of consanguineous marriage.
Split into simpler sentences: FXIIID, while generally rare, does occur, with Iran having the highest global incidence of the disorder with 473 cases. The city of Khash, located in Sistan and Balochistan provinces, has the highest incidence in Iran, with a high rate of consanguineous marriage.