Companies developing products for niche genetic diseases may be required to run only very small pivotal trials, due to the rarity of the given disease. A case in point is BioMarin Pharmaceutical Inc. and Genzyme General, which enrolled only 10 patients in the Phase III study of their Aldurazyme enzyme replacement therapy to treat mucopolysaccharidosis-I (MPS-I).

Now, however, the partners must compile another set of subjects from this tiny but potentially lucrative patient population in order to meet FDA requests for a confirmatory Phase III study, which will delay their proposed BLA filing by about a year to the end of 2000 and anticipated market launch to 2001. Last week's announcement followed a recent meeting with the FDA, which wants additional data supporting Aldurazyme's therapeutic benefit.