Core Insights - The FDA has granted orphan drug designation to rilzabrutinib for two rare diseases, warm autoimmune hemolytic anemia (wAIHA) and IgG4-related disease (IgG4-RD), which currently have no approved treatments [1][2] - Rilzabrutinib is also under regulatory review for immune thrombocytopenia (ITP) in the US, EU, and China, with a target action date for FDA decision set for August 29, 2025 [2][8] Rilzabrutinib Overview - Rilzabrutinib is an investigational, oral, reversible Bruton's tyrosine kinase (BTK) inhibitor, showing potential as a first- and best-in-class treatment for several immune-mediated diseases [5] - The drug utilizes Sanofi's TAILORED COVALENCY® technology to selectively inhibit BTK, potentially minimizing off-target side effects [5] Clinical Data - A phase 2b study on wAIHA indicated that rilzabrutinib treatment resulted in clinically meaningful outcomes regarding response rates and disease markers [3] - In a phase 2a study for IgG4-RD, rilzabrutinib treatment over 52 weeks led to a reduction in disease flare and other disease markers, along with glucocorticoid sparing [4] Disease Background - wAIHA affects 1 to 3 individuals per 100,000 in the US annually and is characterized by the premature destruction of red blood cells, leading to severe fatigue and other symptoms [6] - IgG4-RD affects approximately 8 out of 100,000 adult patients in the US each year and is a chronic condition that can cause organ damage and dysfunction [7]