Hemophilia is caused by a defective or missing clotting factor VIII . This causes a subject to lose excess blood in case of a cut. This clotting factor is coded for a gene in the DNA of the blood platelet cells. A mutation in this gene causes hemophilia.
Genetic engineering allows for gene therapy to be possible to rectify the defective gene. This is done at the embryo stage. The gene in the X chromosome (because this is a sex-linked gene) is rectifying using tools like the CRISPR Cas9 tool.
