BioMarin Pharmaceutical is celebrating the thumbs-up from regulators in Europe for a drug that treats a rare autoimmune disease.

The European Commission has granted marketing approval to amifampridine for Lambert Eaton Myasthenic Syndrome, a disease for which the primary symptom is muscle weakness. The prevalence of LEMS is estimated at four to ten per million, or 2,000-5,000 patients in the European Union and 1,200-3,100 patients in the USA. Approximately 50% of patients diagnosed have small cell lung cancer, BioMarin noted.

The company got hold of the drug through the acquisition in October of Huxley Pharmaceuticals. The latter had licensed amifampridine from EUSA Pharma which in turn had acquired the drug from the original developer, Assistance Publique Hopitaux de Paris.

Jean-Jacques Bienaime, BioMarin’s chief executive, noted that amifampridine is the first approved treatment for LEMS and will have ten years of market exclusivity in Europe. It has also received orphan drug designation across the Atlantic.

He went on to note that the firm is on track to launch amifampridine in the EU in mid-March and will meet with the Food and Drug Administration soon “to determine the necessary regulatory path for this product” in the USA. BioMarin is also looking at other possible indications for the drug, notably multiple sclerosis.

Under the terms of the Huxley deal, BioMarin paid $15.0 million upfront and will now fork out an extra $7.5 million following European approval of amifampridine. Huxley stockholders are also eligible to get up to $36.0 million in milestone payments if the drug does well, while EUSA will benefit financially, depending on successful development in MS.

Amifampridine becomes BioMarin’s fourth approved product, along with Naglazyme (galsulfase) for mucopolysaccharidosis VI (MPS VI), Aldurazyme (laronidase) for mucopolysaccharidosis I, developed through a joint venture with Genzyme Corp, and Kuvan (sapropterin) for phenylketonuria, partnered with Merck Serono.