there is a 60% intermarriage rate. same in saudi arabia. saudi arabia has set up an entire genetics institute for this.
In england it is the same among (asians pakistanis moslems). moslems intermarry at up to a 70% rate and have 3 to 5 times the rate of birth defects than others in britain.
if you google
arab intermarriage birth defect britain asians birth defects saudi arabia
you will find this all out
du might be a factor, but there isnt any DU in london or riyadh