Analysts have interpreted that as giving Genzyme's treatment, Fabryzyme, the inside track toward getting a six-year term of exclusivity under orphan drug laws, which is meant to encourage companies to develop treatments for rare diseases.

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Because BioMarin's drugs serve small patient populations, each drug is granted orphan status upon approval, which means exclusivity for seven years in the U.S. Revenues from one drug should eventually throw off enough cash to fund further drug development, figures Yun.

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The orphan drug act only gives them eight years of exclusivity, but it does set a precedent for giving companies an extension of their monopoly that is not based on patent protection.

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