The U.S. Food and Drug Administration (FDA) has granted accelerated approval to Kebilidi (eladocagene exuparvovec), a gene therapy developed by PTC Therapeutics, for the treatment of aromatic L-amino acid decarboxylase (AADC) deficiency. This marks a significant milestone as the first FDA-approved gene therapy administered directly into the brain.
AADC deficiency is an ultra-rare genetic disorder resulting from mutations in the DDC gene, which impairs the production of neurotransmitters like dopamine. This deficiency leads to severe motor and developmental delays, particularly in infants. Kebilidi aims to address this by delivering a functional copy of the DDC gene directly into the putamen, a brain region crucial for motor control and learning.
Clinical Efficacy
The FDA's approval was based on an open-label study involving 13 pediatric patients aged 16 months to 10 years with severe AADC deficiency, all of whom lacked gross motor function. Compared to the natural history of untreated patients, Kebilidi demonstrated notable efficacy. At 48 weeks post-treatment, eight out of 12 patients showed improvements in gross motor function. Specifically, three patients achieved full head control, and two could sit with or without assistance. Notably, earlier intervention appeared to yield better outcomes, with the two patients who could walk backwards at week 48 having been treated before the age of 2.
Mechanism of Action and Administration
Kebilidi is a gene replacement therapy that utilizes an adeno-associated virus (AAV) to deliver a functional DDC gene to replace the mutated gene. The therapy is administered via a single surgical procedure involving four infusions into the putamen. This approach aims to restore the expression of the deficient enzyme, thereby increasing dopamine production in the brain.
Regulatory and Commercial Context
Kebilidi received European approvals in 2022 for patients 18 months and older and has since been approved in Israel, Brazil, and Taiwan. The FDA's decision is an accelerated approval, contingent on confirmatory evidence from long-term follow-up studies. According to William Blair analyst Sami Corwin, the effects of Kebilidi have shown durability for up to 10 years post-treatment.
Market Impact and Future Prospects
Given the rarity of AADC deficiency (fewer than 350 reported cases), William Blair projects peak revenue of $266.3 million for Kebilidi in 2026. Furthermore, the approval grants PTC Therapeutics a priority review voucher, which can be used to expedite the regulatory review of another rare disease drug candidate. Such vouchers are often sold to larger pharmaceutical companies, as demonstrated by Acadia Pharmaceuticals' recent $150 million sale of their voucher for a Rett syndrome drug.
