Group 1 - Sanofi's investigational BTK inhibitor, rilzabrutinib, received orphan drug designation from the European Medicines Agency (EMA) for treating IgG4-related disease (IgG4-RD) [1][7] - IgG4-RD is a chronic, immune-mediated rare condition that can affect multiple organs, leading to inflammation, swelling, and fibrosis [1] - Rilzabrutinib is currently undergoing a phase II study for IgG4-RD, showing a reduction in disease flare and glucocorticoid sparing over 52 weeks [2][7] Group 2 - Rilzabrutinib is also being developed for immune thrombocytopenia (ITP) and has orphan drug designation for this indication in the United States, EU, and Japan [3] - A regulatory application for rilzabrutinib's approval for ITP is under review in the U.S., with a decision expected by August 29, 2025 [4] - The FDA has granted orphan drug designation to rilzabrutinib for warm autoimmune hemolytic anemia (wAIHA) and sickle cell disease (SCD) [5] Group 3 - Upon potential approval, rilzabrutinib may face competition from existing therapies, such as Rigel Pharmaceuticals' Tavalisse, which recorded $68.5 million in sales in the first half of 2025, a 44% increase year-over-year [6] - Amgen's Uplizna became the first FDA-approved drug for IgG4-RD in April 2025, following its acquisition of Horizon Therapeutics [8]