Inbreeding, I haave read stories that many Saudi pilots have night vision issues as well as others making training them for this aspect near impossible. They intermaqarry cousins etc and the gene pool is becoming polluted and depleted.
Inbreeding seems to be the norm throughout the Arab world - marrying 1st cousins is how they keep their clan loyalties going. I wonder whether inbreeding was one, if not the, main driving forces behind the decline of the Arab/Muslim world between the Middle Ages and modern times.