BioMarin Pharmaceutical is developing laronidase, recombinant alpha-L-iduronidase enzyme replacement therapy for the treatment of mucopolysaccharidosis I (MPS-I) [the most severe form of this is called Hurler syndrome]. The company has received US and European orphan drug designation for the enzyme and has fast-track review status with the FDA. In 1998, BioMarin Pharmaceutical and Genzyme General formed a joint venture for development and marketing of laronidase. A Phase I trial in 10 patients with a range of disease severity of MPS-I required for US and European filing was completed at the Harbor-UCLA Medical Center in California. This open label trial involved weekly infusions with laronidase. The two-year follow-up data revealed sustained and, in certain parameters, improved clinical results recorded at the end of 1 year of therapy. BioMarin and Genzyme General have completed a pivotal, Phase III trial in the centres in the USA, Canada and Europe, including patients with Hurler-Scheie and Scheie syndromes. In a multicentre, double-blind, placebo-controlled study, all 45 patients with MPS-I have received at least their initial weekly infusion of laronidase. Patients are being evaluated over a 6-month period. BioMarin Pharmaceutical and Genzyme General have filed on 15 April 2002 the first portion of a 'rolling' BLA with the US FDA for use of laronidase in the treatment of MPS-I. The companies are planning to complete the BLA filing in Q3 2002. The application will include 6-month data from the ongoing open-label Phase III extension study and also the 6-month data from the placebo-controlled part of the Phase III study. In the open-label extension study, patients from both the treatment and placebo arms of the Phase III trial received weekly infusions of laronidase for at least 6 months. The response from the US FDA is anticipated during the H1 of 2003. Both companies plan to initiate two new clinical trials in patients with MPS-I. One study will enrol patients with MPS-I under 5 years old. Another study will investigate laronidase in patients with advanced clinical symptoms of MPS-I. Additionally, patients from the ongoing Phase III study will continue to receive treatment with laronidase. On 1 March 2002, BioMarin and Genzyme filed a marketing approval application with European regulatory authorities for AldurazymeOE for the treatment of MPS-I. Mucopolysaccharidosis I is a rare autosomal recessive lysosomal storage disorder caused by alpha-L-iduronidase deficiency. Its manifestations in children can include growth and developmental delay, enlargement of spleen and liver, skeletal deformity, cardiac and pulmonary impairment, vision or hearing loss and mental dysfunction. At present, bone marrow transplantation is the only available treatment.