US regulators have issued a green light for Alexion’s long-term enzyme replacement therapy Kanuma, giving patients with the ultra rare genetic disorder lysosomal acid lipase deficiency access to a targeted treatment for the first time.

LAL-D is a chronic, progressive disease that causes chronic build-up of cholesteryl esters and triglycerides in the liver, blood vessel walls and other tissues, leading to multi-organ damage and premature death. 

In clinical studies, 67% of infants treated with Kanuma (sebelipase alfa) survived beyond 12 months of age while none of the infants in the historical control group did, and reductions in important markers of liver disease, including ALT and liver fat content, as well as significant improvements in lipid parameters were observed in both children and adults.

Kanuma will be launched during the first week of January 2016, but until then Alexion said its expanded access programme will remain open to enable patients with LAL-D to continue treatment until the product becomes commercially available.

The drug could be priced at $300,000 to $400,000 annually, according to Morningstar analyst Stefan Quenneville, and UBS analyst Matthew Roden has forecast sales of $410 million by 2019 reaching $1.5 billion at their peak, according to media reports.

The FDA is also currently considering whether to issue a green light for Strensiq (asfotase alfa), Alexion’s enzyme replacement therapy for another ultra-rare condition called paediatric-onset hypophosphatasia. 

Both drugs were cleared in Europe back in September, but UK cost regulators have rejected use of Strensiq on the National Health Service in England and Wales because the firm failed to adequately justify the drug’s high cost (£336,000 per patient per year).