The FDA approved Mirum Pharmaceuticals’ zilurgisertib (Atebrioz), the third treatment for an ultra-rare genetic disorder that causes muscle and connective tissue to turn into bone. Zilurgisertib blocks the ALK2 receptor, targeting the pathway driving disease progression. For affected patients and clinicians, the approval adds another mechanism to the treatment menu and may influence long-term management strategies, including mobility, pain control, and functional preservation. As with other ultra-rare therapies, uptake will be shaped by eligibility criteria, payer coverage, and real-world safety monitoring. Regulators’ decision also provides a further signal that ALK2 inhibition remains a validated therapeutic approach in this disease category, supporting continued development of pathway-focused agents.