Genetic disorders are caused by genetic mutations (changes) in your gene. Over the past decade especially, researchers increasingly explore genome editing options to fix or address genetic diseases at the source: literally at your DNA. Two of these options are base editing and prime editing.

Base editing looks at your DNA (which includes A, T, C, and G). Sometimes, one of those letters is wrong. Base editing uses CRISPR-Cas9 with a deaminase enzyme to “erase” and change that one letter – without making any broader changes. Prime editing is slightly more in-depth and complex; it can be used not just to change one letter, but to add, remove, or replace letters.

Dr. Megan Garlapow, PhD recently discussed the use of base and prime editing for hemophilia A in Rare Disease Advisor.

What is Hemophilia A?

Also known as factor VIII deficiency, hemophilia A is a rare inherited genetic bleeding disorder. Hemophilia A is characterized by a genetic deficiency of clotting factor VIII. This means that the blood doesn’t clot as well as it could, leading to excessive and prolonged bleeding. Hemophilia A primarily affects males.

In her article, Dr. Garlapow discusses a study exploring base editing and prime editing in hemophilia A. The study, published in the Journal of Thrombosis and Haemostasis, explains that factor VIII replacement therapies – as well as some non-replacement therapies – are effective in controlling hemophilia A bleeds. However, individuals taking these medications require life-long treatment. The study authors question how base and prime editing could transform this field.

To begin, the research team sourced human embryonic kidney 293T cells that expressed factor VIII variants (mutations). Next, they used lipofectamine 2000 to deliver plasmids with base editing and prime editing systems, as well as factor VIII vectors, to the cells. They additionally quantified protein expression in the cells, and validated how effective and efficient the DNA editing was.

The research team found that base and prime editing:

• Increased factor VIII secretion and activity by 20-30% in stable cell clones
• Improved factor VIII expression by up to 25% in wild-type factor VIII for cells with p.R2166 and p.R2228Q mutations

Ultimately, these results suggest that base editing and prime editing could be effective interventions for hemophilia A. However, it is important to note that this study was only performed in cell cultures. Additional research into base and prime editing for mice and animal models with hemophilia A mutations is needed before this can reach the clinical setting.