BioMarin will be breathing a sigh of relief after US Food and Drug Administration advisors backed its rare growth disorder drug Vimizim.

Vimizim (GALNS) is under priority review at the FDA for the treatment of lysosomal storage disorder Mucopolysaccharidosis Type IVA (MPS IVA), also known as Morquio A Syndrome.

Of the 21 panellists, 19 voted in favour of approving the enzyme replacement therapy for use in all patients, one backed its approval for a subgroup of patients, and one voted against clearance.

Backing was based on data from the MOR-004 study, which showed that patients taking a weekly dose of Vimizim showed a significant improvement of 22.5 metres in the six-minute walk test compared to those in the control arm.

On the secondary endpoint of three-minute stair climb, patients on BioMarin's therapy showed a trend toward improvement at 24 weeks of 1.1 additional stairs per minute over placebo.

"We are thrilled to have achieved this important milestone in our mission to bring the first approved therapy to treat Morquio A patients," said Jean-Jacques Bienaimé, the firm's chief executive, commenting on the panel vote.

The FDA is not bound to follow the recommendations of its advisory panels, but is set to make its decision by the end of February. 

The estimated prevalence of MPS IVA is around 3,000 patients in the developed world, and analysts are forecasting peak sales of Vimizim of to hit around $800 million.