Researchers reported that patients with hemophilia B who received a single administration of etranacogene dezaparvovec would likely have enough factor IX (FIX) levels to remain free from the need for prophylactic FIX replacement products for more than 2 decades, according to a study published in Current Medical Research and Opinion. 

“Gene therapy offers the potential for a new treatment paradigm for people with hemophilia,” the authors of the study wrote. 

Congenital hemophilia B is caused by a deficiency in the blood coagulation factor FIX. In severe forms in which the circulating levels of FIX fall below 1%, symptoms appear early in life; these include spontaneous bleeding episodes without recognized trauma. The recurrence of these bleeding episodes throughout life can result in arthropathy, limiting mobility and causing chronic pain. 

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Etranacogene dezaparvovec is one such gene therapy, in which adeno-associated viral vector serotype 5 capsids contain the coding sequence for human FIX. Open-label, multicenter trials have validated its initial efficacy endpoint. Research is ongoing into the long-term durability of these results. 

Read more about hemophilia etiology 

The authors of the study used statistical modeling to estimate the long-term durability of etranacogene dezaparvovec based on data obtained from phase 2b and phase 3 clinical studies. The data of all the participants in those trials (n=55) were included. The researchers then transformed FIX levels from their original scale to log scale for statistical modeling. 

The research team discovered that a single administration of etranacogene dezaparvovec would likely be sufficient for more than 80% of patients to be free from the need for prophylactic FIX replacement products for 25.5 years, demonstrating the long-term durability of this form of gene therapy. 

“Having etranacogene dezaparvovec as a novel, alternative treatment option would ultimately benefit people with hemophilia B,” the authors of the study concluded. 


Shah J, Kim H, Sivamurthy K, Monahan PE, Fries M. Comprehensive analysis and prediction of long-term durability of factor IX activity following etranacogene dezaparvovec gene therapy in the treatment of hemophilia BCurr Med Res Opin. 2022;1-11. doi:10.1080/03007995.2022.2133492