Ultragenyx (NASDAQ:RARE), a biopharmaceutical company focused on the development and commercialisation of novel therapies for rare and ultra-rare genetic diseases, announced that the UK Medicines and Healthcare products Regulatory Agency (MHRA) accepted on 28^th October 2026 the Company’s Marketing Authorisation Application (MAA) for rebisufligene etisparvovec (also known as rebi-vec or UX111), an investigational gene therapy for the treatment of mucopolysaccharidosis Type IIIA (MPS IIIA), also known as Sanfilippo syndrome Type A.

Sanfilippo syndrome Type A is a rare, progressive, inherited disorder associated with severe neurological impairment and significant unmet medical need. Currently, treatment options remain limited for affected children and their families.

MHRA acceptance confirms that the application is sufficiently complete for the Agency to begin its formal scientific review of UX111, which remains investigational in the UK. There can be no assurance that marketing authorisation will ultimately be granted.

“The acceptance of our application by the MHRA marks an important regulatory milestone in the ongoing review process for this investigational therapy,” said Jane Cooper, Senior Vice President and Region Head for Europe, Middle East and Africa at Ultragenyx. “We recognise the profound unmet need within the Sanfilippo syndrome Type A community and are working with urgency to advance our regulatory strategy. To enable sustainable access on the NHS for eligible children, we have agreed to schedule the NICE evaluation to align with the Marketing Authorisation Application review with the ambition to receive a NICE decision as close as possible to a potential regulatory approval”.

Ultragenyx also announced last month the start of the European Medicines Agency (EMA) Marketing Authorisation Application review.

The MHRA is responsible for assessing the product’s quality, safety and efficacy for regulatory authorisation. The National Institute for Health and Care Excellence (NICE) is responsible for appraising the clinical and cost-effectiveness to inform NHS funding decisions in England. The NICE Prioritisation Board previously routed the treatment to the Highly Specialised Technology programme (HST) after agreeing that it meets all four of the criteria of the HST framework, including that it is an innovation to treat an ultra-rare and debilitating condition.