US regulators have rejected Akcea/Ionis’ application to market Waylivra for the ultra-rare rare lipid disorder familial chylomicronemia syndrome (FCS).

The companies said they have received a complete response letter from the US Food and Drug Administration, but did not reveal the reasons for the rejection.

The news came as somewhat of a surprise given that the FDA’s Endocrinologic and Metabolic Drugs Advisory Committee (EMDAC) voted 12-8 in favor of approving Waylivra (volanesorsen) in May.

FCS is a severe, potentially fatal disorder where patients have extremely high levels of triglycerides in their blood, causing a range of symptoms including potentially fatal attacks of acute pancreatitis.

People with the condition are unable to metabolise large triglyceride-rich lipid particles called chylomicrons due to a deficiency in lipoprotein lipase, an enzyme that helps to break down triglycerides.

Currently, the only option for patients is a severely restricted low fat diet of 10-20 grams of fat a day, which, even when strictly adhered to, does not decrease triglycerides to normal levels or remove the threat of pancreatitis for most patients.

Volanesorsen is also under review in Europe, but is already available to FCS patients in the UK under the Medicines and Healthcare products Regulatory Agency’s Early Access to Medicines Scheme.

Data from the Phase III APPROACH trial showed that Waylivra-treated patients achieved a significant reduction in triglycerides of 77 percent after three months’ treatment, compared to rise of 18 percent in the placebo group.