Patients in Europe with the ultra rare blood clotting disorder acquired thrombotic thrombocytopenic purpura (aTTP) are a step closer to getting the first therapeutic specifically indicated for treating the disease, after Ablynx filed for approval of caplacizumab.

The life-threatening disorder has a sudden onset caused by impaired activity of the ADAMTS13 enzyme, resulting in severe thrombocytopenia (very low platelet count) and micro-clot formation in small blood vessels throughout the body which cause thrombotic complications and widespread organ damage.

Despite the current standard-of-care treatment of PEX and immunosuppression, episodes of aTTP are still associated with a mortality rate of up to 20 percent, and patients are at risk of acute thromboembolic complications such as stroke, venous thrombosis and myocardial infarction as well as a recurrence of the disease.

In a Phase II clinical trial, treatment with caplacizumab resulted in a nearly 40 percent reduction in time to platelet count normalisation as compared to placebo, and also reduced recurrences of aTTP by 71 percent.

In a post-hoc analysis of trial data, a clinically meaningful lower proportion of subjects treated with the drug experienced one or more major thromboembolic events, or died, as compared to placebo (11.4 percent versus 43.2 percent, while fewer caplacizumab-treated patients were refractory to treatment.

The Phase III HERCULES study in patients with aTTP is currently ongoing and is expected to support a BLA filing in the US.

"As pioneers in the treatment of aTTP, we are committed to making caplacizumab available to patients suffering from this severe disease for which there is currently no specifically approved drug available," said Dr Edwin Moses, Ablynx' chief executive. "This is a very important moment in the development of Ablynx, as we prepare to commercialise our first product and become a fully vertically integrated biopharmaceutical company."

Caplacizumab received Orphan Drug Designation in Europe and the US back in 2009.