Early results have been remarkable, with the first 164 patients who received the treatments showing promising outcomes; new hope for SCD is on the horizon. 

What is Sickle Cell Disease? 

SCD is a rare but devastating inherited blood disorder caused by a single point mutation in the beta-hemoglobin (β-globin) gene. In a healthy person, red blood cells are round and smooth, and they flow through blood vessels easily. In someone with SCD, when their red blood cells deliver oxygen to the body, they contort into the shape of a sickle. The misshapen cells cluster together, forming blockages that disrupt healthy red blood cells from delivering oxygen to the body’s muscles and tissue. The result is a lifetime of severe pain episodes, also known as vaso-occlusive episodes (VOEs), strokes, organ damage, and, in many cases, premature death. 

The disease is passed down through families following what scientists call an autosomal recessive inheritance pattern. Meaning that children can develop SCD when they inherit a copy of the mutated gene from both parents. If a child inherits just one copy, they have what is known as the sickle cell trait. People with the trait usually lead normal, symptom-free lives, but they carry the gene and can pass it on to their own children. When both parents are carriers, there is a 25% chance their child will have the full disease, a 50% chance their child will be a carrier like them, and a 25% chance their child will inherit neither copy of the mutated gene.

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The Devastating Effects of SCD Across Communities 

SCD’s reach is staggering, and its death toll and impact globally are far more pervasive than recorded. In 2021, an estimated 7.4 million people worldwide were living with SCD, primarily in Sub-Saharan Africa, which accounts for 80% of global cases. Among children under five, sickle cell disease caused approximately 81,100 deaths in 2021, ranking it as the 12th leading cause of death in that age group globally. Without intervention, estimates suggest that up to 90% of individuals with SCD in Africa will not make it to 18 years of age.

In the United States, the picture is comparatively better but still harrowing. SCD affects 100,000 people, more than 90% are African American, and an estimated 3%–9% are Hispanic or Latino. In 2020 alone, there were 1,023 documented SCD-related deaths in the US, a 12% increase from prior years, partly linked to the COVID-19 pandemic. Even with access to modern medicine, the disease reduces patients’ life expectancy in the U.S. by an average of 20 years.

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Introducing Gene Therapy

Before gene therapy, SCD was managed entirely through symptom prevention, pain control, and supportive care. Daily medications, blood transfusions, and stem cell transplants were the only options for treatment. But in 2023, the FDA approved two milestone treatments: Casgevy and Lyfgenia. These represent the first cell-based gene therapies for the treatment of SCD in patients 12 years and older.

Casgevy: Made by Vertex Pharmaceuticals & CRISPR Therapeutics

Before babies are born with SCD, they produce a special form of hemoglobin called HbF (fetal hemoglobin) while still in the womb. Fetal hemoglobin is resistant to sickling. Shortly after birth, the body switches it off and starts producing adult hemoglobin instead. In sickle cell patients, adult hemoglobin is the defective form. 

During Casgevy treatment, patients first have to undergo myeloablative conditioning, a high-dose chemotherapy regimen, to remove the affected cells. Then the patient’s own blood stem cells are extracted and edited outside the body using CRISPR/Cas9 technology. The gene editing therapy makes the BCL11A gene, which is responsible for shutting off fetal hemoglobin production, inactive. When you stop BCL11A, you simultaneously increase fetal hemoglobin and repress sickle hemoglobin. 

The results from clinical trials were striking: 96.7% of patients had zero vaso-occlusive crises for at least one year after treatment, and 100% remained hospitalization-free for the same period. 

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Lyfgenia: Made by Bluebird Bio

While Casgevy works by editing an existing gene, Lyfgenia takes a different approach; it introduces a new gene. Lyfgenia is designed to provide patients with a modified copy of the HBB gene that produces a form of hemoglobin called HbAT87Q, which carries anti-sickling properties. 

Again, before treatment, patients must undergo high-dose chemotherapy. Then the modified gene is delivered into the body using a harmless virus called a lentiviral vector. This carries the genetic instructions into the stem cells like a molecular courier. After a single intravenous infusion, the modified stem cells engraft in the bone marrow and begin producing red blood cells containing the new hemoglobin, which is resistant to sickling. 

Long-term data have been equally promising: as of mid-2024, all evaluated patients continued to show stable production of anti-sickling hemoglobin. In December 2024, 21-year-old Sebastien Beauzile became the first patient from New York to be treated with Lyfgenia and has been free of symptoms ever since.

Equitable Care and the Access Problem 

While gene therapy could potentially cure existing cases of SCD, the price of the treatment excludes the majority of patients from accessing it. Casgevy lists for $2.2 million, while Lyfgenia lists for $3.1 million, a price range that is out of reach for many living with SCD. 

Despite the historic approvals, uptake of both treatments has been slow. In the first quarter of 2025, Vertex reported that eight patients had completed the treatment, whereas Bluebird Bio reported four. 

For the first time in history, we have the science to potentially cure Sickle Cell Disease, but there is still much work to be done before gene editing therapy is available to everyone. 

Patient in a hospital bed, Source: Freepik

The post How Gene Therapy Could End Sickle Cell Disease appeared first on UrbanGeekz.