Gene-editing treatment Casgevy extended to UK children aged five

Children in the UK as young as five with severe sickle cell disease or transfusion-dependent beta-thalassaemia can now be considered for Casgevy, the CRISPR gene-editing treatment. The MHRA announced the extension on 30 October 2026; the licence change was granted the day before. The treatment was previously licensed only for people aged 12 and over.

NICE updated both of its Casgevy appraisals the same day, so eligible children aged 5 to 11 in England can be treated through the existing managed access arrangements, under the same criteria as older patients.

The move follows the US, where the FDA extended Casgevy to children aged 2 and over in July 2026. The evidence in children is small, based on about two dozen patients aged 5 to 11, but the early results mirror those seen in adults and teenagers.

What the MHRA approved

According to the MHRA:

Julian Beach, MHRA Executive Director Operations, said: "This approval means this innovative gene-editing treatment can now be used in eligible children from the age of five, extending this treatment option to younger patients."

How Casgevy works

Both conditions are caused by faults in the genes for haemoglobin, the protein red blood cells use to carry oxygen.

• In sickle cell disease, red cells can become rigid and sickle-shaped, causing attacks of severe pain known as vaso-occlusive crises, serious infections, anaemia and organ damage.
• In beta-thalassaemia, the body makes too little working haemoglobin. People with the transfusion-dependent form often need blood transfusions every three to five weeks for life.

Casgevy edits a person's own blood stem cells so they produce more fetal haemoglobin, a form normally switched off after birth. Fetal haemoglobin works in both conditions: it stops red cells sickling and makes up for the missing adult haemoglobin.

The process takes months:

1. Stem cells are collected from the patient's blood.
2. They are edited in a laboratory using CRISPR/Cas9.
3. The patient receives high-dose chemotherapy, called conditioning, to clear space in the bone marrow.
4. The edited cells are infused back as a one-off treatment.
5. The patient stays in hospital while the new cells settle in and start making blood.

The evidence in children

The paediatric data come from two ongoing phase 3 trials, CLIMB THAL-141 in thalassaemia and CLIMB SCD-151 in sickle cell disease. Results were published in the New England Journal of Medicine in June 2026.

The FDA's July summary, using a slightly different data cut, reported that eight of nine assessable children with thalassaemia achieved at least 12 months in a row without transfusions, with a median of 20.1 months free of them.

These are single-arm trials with no comparison group. That is usual for one-off treatments in rare, serious conditions, where a placebo arm would mean putting children through stem cell collection for nothing. But it means the numbers are small and follow-up is short.

How the results compare with older patients

The NEJM authors note that in the earlier phase 3 studies, in people aged 12 to 35, exa-cel eliminated vaso-occlusive crises and the need for red-cell transfusions in most patients. The children's results so far point the same way. The question regulators had to answer was whether the benefit and the conditioning risks balance out similarly in younger children. The MHRA concluded that they do.

Safety

The main risks come from the conditioning chemotherapy, which uses busulfan. It wipes out the existing bone marrow and leaves people vulnerable to infection and bleeding for weeks. It can also affect fertility, which is a particular concern for children and their families.

The MHRA lists nausea, fatigue, fever and an increased risk of infection among the side effects. The FDA reported mucositis (painful inflammation of the mouth and gut lining) and fever with low white cell counts as the most common reactions in children.

In the NEJM report, every child had at least one grade 3 or 4 adverse event. Two children with thalassaemia developed severe veno-occlusive disease, a liver complication, which was assessed as related to busulfan conditioning. One of them died.

Families need to weigh these risks carefully. Specialist teams usually discuss fertility preservation before conditioning.

Who is eligible in England

NICE's sickle cell guidance (TA1044) covers people with severe disease who have recurrent vaso-occlusive crises, certain genotypes, are suitable for a stem cell transplant and do not have a matched related donor. The thalassaemia guidance (TA1003) covers transfusion-dependent disease. Both now apply from age five.

Both appraisals are under managed access. That means the NHS funds the treatment while more evidence is collected, after which NICE will decide whether to recommend it for routine use. The price paid by the NHS is confidential, set out in a commercial access agreement.

Treatment is given in a small number of specialist centres. Families interested should ask their child's haematology team for a referral.

Why treat younger children

The FDA's paediatric reviewer argued that earlier treatment may reduce the risk of lasting organ damage. Sickle cell disease can damage the brain, lungs, kidneys and other organs from early childhood, and frequent transfusions in thalassaemia lead to iron overload.

The counterargument is uncertainty. The long-term effects of gene editing, and of conditioning chemotherapy given in early childhood, will only become clear with years of follow-up. Vertex and regulators are collecting long-term data.

How many people could benefit

The MHRA says about 15,000 people in the UK have sickle cell disorder. Only a fraction would meet the criteria for Casgevy, and fewer still are children aged 5 to 11. Treatment capacity, the need for long hospital stays and the conditioning risks will also limit numbers.

Families should talk to their specialist team about whether their child qualifies.

This article explains published research and isn't medical advice. Talk to your own doctor or specialist team before changing any treatment.