Geneticists have used a cutting-edge DNA base editing treatment on several patients to cure thalassemia, a prevalent and severe genetic blood disease.
China announced Wednesday that four children with thalassemia, a severe genetic blood disorder usually diagnosed in toddlers, have been cured using a domestically developed DNA base editing therapy.
Thalassemia damages hemoglobin — the protein in red blood cells that carries oxygen — reducing the body’s ability to transport it efficiently. Sufferers tend to exhibit a range of symptoms including fatigue, weakness, stunted growth, and facial bone deformities.
The treatment is currently under clinical research led by hematologist Professor Zhai Xiaowen at the Children’s Hospital of Fudan University, in Shanghai.
In the trials, four child patients — three from China and one from Pakistan — were given a single injection of CS-101, an experimental drug developed by CorrectSequence Therapeutics, a biotech firm related to ShanghaiTech University.
The drug uses a transformer base editor, or tBE, to correct thalassemia’s disease-causing DNA mutation, restoring normal hemoglobin function.
In December 2024, a 14-year-old boy from eastern Jiangxi province became the first patient cured in the trial jointly conducted by CorrectSequence and Fudan University — just five weeks after treatment.
The youngest and most recent case, a 4-year-old girl from Pakistan, received the injection in January 2025 and was deemed cured after three months.
The 14-year-old boy at the Children’s Hospital of Fudan University, in Shanghai, December 2024. From the Paper
Thalassemia is prevalent in regions historically affected by malaria, giving it its alternative name, “Mediterranean anemia.” It is also common in Southeast Asia and southern China, especially in Guangdong province and neighboring Guangxi Zhuang Autonomous Region.
But due to increased population mobility over the past four decades, what was once a regional disease has spread to central and northern parts of China.
According to a 2020 report, it is estimated that around 30 million people in China carry some form of the thalassemia gene, making it one of the most common hereditary blood disorders in the country. Around 300,000 currently live with moderate to severe forms of the disease, with patient numbers increasing by roughly 10% each year.
Two main types of thalassemia exist, alpha and beta, depending on which part of the hemoglobin molecule is affected. Each condition further classified as mild, intermediate, or severe.
Many infants with severe alpha thalassemia die before or shortly after birth, while patients with severe beta thalassemia who do not receive timely treatment have an average life expectancy of just 15 years.
Prior to CS-101, two main, invasive treatments existed for severe beta thalassemia: regular, lifelong blood transfusions, or a one-off (if successful) transplant of blood-generating stem cells or bone marrow costing between 300,000 and 600,000 yuan ($41,500-83,000). However, due to low donor compatibility and high surgical risks, transplants are not widely accessible globally.
With new advances in biotechnology, gene editing has emerged as a promising alternative for treating thalassemia. For example, CRISPR-based therapies — which involve precisely detecting and modifying faulty genes in the DNA sequence — have been commercially available in the U.K. and U.S. since 2023.
Base editing is a newer and more precise tool, Gao Caixia, a geneticist at the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, explained to domestic media in 2022.
Describing the treatment, she said: “If one of the four DNA letters — A, T, C, and G — is wrong, you can think of it like using an eraser to remove it, then writing in the correct letter with a pencil.”
This method is also less likely to trigger unintended knock-on effects.
“It avoids risks such as large-scale DNA deletions, chromosomal mutations, and off-target effects, demonstrating better efficacy and safety,” the developer, CorrectSequence Therapeutics, wrote in its product briefing.
Professor Zhai Xiaowen told domestic outlet The Paper that her team began collaborating with CorrectSequence Therapeutics in 2023. At the time, they undertook an investigator-initiated trial (IIT) of CS-101 — a small-scale study used to test promising therapies prior to formal regulatory approval.
In January 2024, CorrectSequence also partnered with Guangxi Medical University to conduct an IIT of the same treatment. During those trials, a minor with a severe case of thalassemia was cured — the first ever successful case using a base editing treatment. An adult patient who underwent the same treatment was later reported to be recovering from the disease.
In April 2024, the CS-101 injection received official approval from China’s National Medical Products Administration (NMPA) to begin formal, larger-scale clinical trials. Trials are also underway in the U.S. and U.K.
Still, scientists remain cautious about the future of such gene therapies, noting that the thalassemia gene may have been naturally selected for its malaria-resistant traits.
Removing such genes may therefore have unforeseen consequences, prompting researchers to call for at least a decade of long-term monitoring and analysis following treatment.
Editor: Tom Arnstein.
(Header image: Shijue AIGC/VCG)