Spruce Biosciences Sees 1,600% Surge in Stock After FDA Grants Breakthrough Designation for Rare Disease Drug

Spruce Biosciences' stock surged over 1,600% after the FDA granted its rare disease drug a breakthrough designation for Sanfilippo syndrome type B. This designation provides regulatory guidance and allows the use of a key biomarker to determine clinical benefit. The FDA also confirmed the use of improvements in the biomarker as a basis for accelerated approval.

Spruce Biosciences' stock surged by over 1,600% following the U.S. Food and Drug Administration (FDA) granting a breakthrough therapy designation to its rare disease drug, Tralesinidase Alfa enzyme replacement therapy (TA-ERT), for the treatment of Sanfilippo syndrome type B (MPS IIIB). This designation, which aims to expedite the development and regulatory review of promising therapies for serious or life-threatening conditions, comes with significant implications for the company and the affected patient population.

The FDA's decision is based on integrated long-term clinical data demonstrating normalization in cerebral spinal fluid heparan sulfate non-reducing end (CSF HS-NRE), a key biomarker. The agency confirmed that CSF HS-NRE is a surrogate biomarker reasonably likely to predict clinical benefit and could serve as a basis for accelerated approval. This designation facilitates more intensive FDA guidance, cross-disciplinary collaboration, and eligibility for rolling submission and priority review.

Sanfilippo syndrome type B is an ultra-rare, serious, and fatal genetic disease characterized by a deficiency in N-acetyl-alpha-glycosaminidase (NAGLU), an enzyme required for the catabolism of heparan sulfate (HS) in lysosomes. The accumulation of toxic levels of cerebral spinal fluid heparan sulfate in the brain is the underlying pathophysiology of MPS IIIB. The disease affects fewer than 1:200,000 people in the United States, with no FDA-approved therapies currently available. Management of the disease consists of limited palliative care to improve quality of life.

Tralesinidase Alfa Enzyme Replacement Therapy (TA-ERT) is a fusion protein comprised of recombinant human alpha-N-acetylglucosaminidase (rhNAGLU). The therapy is intended as an enzyme replacement therapy for the treatment of patients with MPS IIIB who lack rhNAGLU enzyme activity. TA-ERT is expected to restore rhNAGLU enzyme activity in the central nervous system following intracerebroventricular injection. The fusion protein enhances its therapeutic potential by binding to the cation-independent mannose-6-phosphate on cell surfaces, enabling the enzyme to be internalized and delivered to the lysosome.

Spruce Biosciences, a late-stage biopharmaceutical company focused on developing and commercializing novel therapies for neurological disorders with significant unmet medical need, is preparing to submit the Biologics License Application of TA-ERT for the treatment of MPS IIIB in the first quarter of 2026. The company's CEO, Javier Szwarcberg, M.D., M.P.H., expressed satisfaction with the designation, highlighting TA-ERT's potential to transform the treatment landscape for MPS IIIB.

The breakthrough therapy designation provides a significant boost to Spruce Biosciences' stock, with investors anticipating the potential of TA-ERT to preserve neuronal cell health and potentially halt or slow neurological decline in affected patients. The designation also highlights the company's commitment to developing innovative therapies for rare neurological disorders.