Islamic scripture condemns riba, an Arabic word meaning excess, which is commonly interpreted as usury. Some Islamic law scholars assert that all interest is prohibited. Others say that only excessive interest is prohibited and that interest is an indispensable part of society that a logical God wouldn't condemn.

Throughout history, interest was common in the Islamic world in places such as the Ottoman Empire, Kuran said. Controversy over the practice emerged only during the 1940s, when Indian Muslims cited the need for an interest-free banking system as one reason they needed a homeland separate from Indian Hindus, Kuran said.

Industry advocates counter that even if some financial transactions serve the same purpose as interest, that doesn't mean they are forbidden by Islam.

"It's possible, as it is in many ethical and legal systems, for two different actions to have the same outcome but, because of the way they're done, for one to be wrong or illegal in that ethical or legal system, and for the other to be permissible or lawful," said Taha Abdul-Basser, an Islamic law scholar with the Islamic Finance Project at Harvard Law School.

In the same year, Kabiri (1995), in his article on the frequency of phenylketonuria
(PKU) in consanguineous couples in Iran, reported that the disorder was three times more frequent in children born out of consanguineous marriages than among the non-consanguineous couples. Earlier Ameli and associates (1988) reported that out of 200 cases of PKU studied
by them in seven years’ span (1979-1986) in a local hospital in Tehran, the frequency recorded was 1 in 4000 live births as against 1 in 10,000 live births in the US. Iran had the highest figures when compared to some other countries like North Ireland (1 in 4,500), Greece, Poland and Scotland (1 in 8,000) and Japan and Denmark (1 in 60,000), the last two countries having implemented the most advanced preventive measures to combat PKU (Ghiyasvand 1995).