Three fascinating advances in rare diseases

New treatments are beginning to reach people with conditions that once had few, if any, options 

More than 300 million people worldwide live with a rare disease. Therefore, the name can be misleading. Whilst each condition affects a relatively small number of people, together it represents a major health challenge. Many begin in childhood and, for most, there is still no approved treatment. 

However, recent progress offers genuine cause for optimism. Gene therapies are now reaching patients, while researchers have developed a treatment tailored to the genetic mutation of one child. Rare disease development remains difficult, but these advances point to new treatment options for conditions once considered untreatable. 

A CRISPR treatment made for one child 

In 2025, a team at Children’s Hospital of Philadelphia and Penn Medicine treated an infant known as KJ, who was born with severe CPS1 deficiency. His liver could not process ammonia properly, allowing toxic levels to build in his blood and putting him at risk of brain damage, coma and death. 

The team designed a base-editing treatment for KJ’s genetic variant. Base editing is a form of CRISPR that changes a single letter of DNA without cutting both strands. The treatment was carried to his liver in lipid nanoparticles, a delivery system also used in some messenger RNA medicines. 

KJ tolerated the treatment and was later able to eat more protein and rely on less medication. It is an extraordinary result, but it comes from one patient, and the follow-up remains limited. Of course, we do not yet know whether this approach can be repeated safely or produced at a cost that health systems can support. Even so, researchers and regulators now have a real case to learn from.

Treating MLD before symptoms take hold 

Metachromatic leukodystrophy (MLD) is an inherited neurological condition. A faulty ARSA gene means the body cannot make enough of an important enzyme, so harmful fatty substances build up in the brain and nervous system. Children can lose the ability to walk, talk and swallow, sometimes very quickly once symptoms appear. 

In March 2024, the FDA approved Lenmeldy for certain children with early-onset MLD. Doctors collect the child’s blood stem cells and add a working copy of the ARSA gene in a laboratory. The modified cells are then returned to the child through an infusion. 

Lenmeldy is given once and is designed to tackle the cause of MLD. However, it needs to be used before the disease has caused too much damage. For families, this makes an early diagnosis just as important as the treatment itself. Wider genetic testing and newborn screening could determine whether an eligible child receives treatment in time. 

Using a patient’s own skin to heal chronic wounds 

Recessive dystrophic epidermolysis bullosa causes extremely fragile skin. Everyday friction can lead to blisters and tears, while wounds may remain open for years. The condition is caused by changes in the COL7A1 gene, which the body needs to make the collagen that holds layers of skin together. 

Zevaskyn, approved by the FDA in April 2025, uses a patient’s own cells to treat these wounds. Doctors take a small skin sample, add working copies of COL7A1 and grow the corrected cells into sheets. These sheets are then grafted onto the areas that need treatment. 

Because every sheet is made for an individual patient, the manufacturing process matters enormously. The cells must be collected, corrected, grown, transported and returned for surgery without losing their quality. In this case, manufacturing is not a separate step behind the science. It is part of the treatment. 

Getting treatment to the people who need it 

These treatments show why rare disease development is difficult. Patients can spend years waiting for a diagnosis. Trials must be recruited from small populations spread across different countries. Some products are made from living cells or developed for one person, which place unusual demands on laboratories, hospitals and supply chains. Health systems must then decide how to fund a treatment with a high upfront cost and benefits that may last for years. 

Companies working in rare disease need leaders who understand these practical constraints. Clinical teams must be comfortable with real-worldInsights data and small trials. Regulatory and manufacturing specialists need to work closely from an early stage, while market access leaders should be speaking to payers well before approval. Patient organisations belong in those conversations too. They understand the effect of delayed diagnosis and can explain which outcomes make the greatest difference to daily life. 

Lenmeldy, Zevaskyn and KJ’s treatment address very different conditions, but each begins with a detailed understanding of the underlying biology. The opportunity now is to turn that scientific precision into treatments that can be made reliably, delivered safely and accessed by more of the people who need them. 

If you work in the rare diseases sector and are looking to expand a C-suite or executive team, reach out directly to the Mx team. They will be in touch to get the process started or answer any questions. Or, learn more about Mx here.