Sheikh Yusuf Talal DeLorenzo, 59, is one such top scholar and works from a Toll Brothers (nyse: TOL - news - people ) mansion in the suburbs of Washington, D.

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"It's a limited specialization with limited practitioners, and even among the people with the specialization only a handful are suitable for working with international financial institutions, " said Yusuf Talal DeLorenzo, a U.S.-based scholar who is one of the chosen few.

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