Your DNA is made up of 4 bases: A, C, G, and T. Beta-Thalassemia is an inherited blood disorder mainly caused by mutations (i.e. changes to these bases) in the HBB gene. A common specific mutation that causes beta-thalessaemia is a change of a single base from the an A base to a G base. Patients with this particular mutation may develop severe anaemia.
Researchers at Sun Yat Sen University in China used a new base editor technology to change the mutated G base back to an A base. The experiment was carried out on lab-made embryos created from the skin cells of a patient with the condition fused to cultured oocytes (egg-cells).
While this study lays the foundations for future developments of treatments for other diseases caused by point mutations such as sickle cell anaemia and cystic fibrosis, please note that study was done in-vitro (i.e. cultured cells inside flasks), and the efficiency of repairing mutations in this study was only about 20%.
Link to the study: https://link.springer.com/article/10.1007/s13238-017-0475-6