Dear Sanfilippo Community,

On Rare Disease Day, we are honored to recognize the strength and resilience of the Sanfilippo community. Over the past year, we have taken important steps to advance the tralesinidase alfa enzyme replacement therapy (TA-ERT) program for individuals and families affected by Sanfilippo Syndrome Type B (MPS IIIB). As we move this program forward, we are committed to building a strong partnership with the patient community, listening closely, and reflecting their priorities in how we plan, communicate, and execute.

While Spruce is relatively new to the Sanfilippo community, our team is experienced in rare disease drug development. Our team has spent much of our careers developing new therapies for rare diseases. Personally, I have dedicated nearly 10 years to rare disease drug development and over two decades advancing new medicines to patients, including enzyme replacement therapies. We approach this work with humility and with respect for the community’s knowledge, recognizing that we are strongest when we learn directly from the people most impacted.

That perspective guides our approach to advancing TA-ERT. Our north star is a patient- and family-centered approach grounded in transparent communications, partnership with the community, and a commitment to doing this work the right way.

In that spirit, I’m pleased to share that we’ve recently made significant regulatory progress that brings us closer to our shared goal of providing a much-needed therapy to the families impacted by MPS IIIB.

In recent months, we have completed two successful meetings with the U.S. Food and Drug Administration (FDA) that have provided us greater clarity on the next steps needed to submit our Biologics License Application (BLA), which the FDA will review as it makes decisions on the potential approval of TA-ERT. We also have engaged with leaders in the patient community to ensure that we are integrating what matters most to those living with this condition. Together, these interactions represent important progress for the TA-ERT program and provide a clear path as we prepare our planned BLA submission in the fourth quarter of this year.

Rare Disease Day is an important time to reflect on progress and reaffirm our gratitude and commitment to the Sanfilippo community, especially the patients, families, advocates, and clinicians waiting for new options. It reminds us that behind every clinical research trial is a community that depends on our urgency, scientific rigor, and resolve. Together, we commit to advance science, deliver hope, and turn possibility into therapies that will make a difference.

Thank you for allowing us to join you in this journey. Together, we will keep moving forward.

With warmest regards,

and the entire Spruce Family