XIAP and Immunodeficiency: In addition, it is necessary to distinguish fHLH from a variety of similar diseases, including congenital immune system deficiencies (such as SH2D1A and XIAP-related lymphoproliferative disorders), combined immune deficiencies (RAG1 and IL27RA), hereditary inflammasome deficiencies (NLRC4 and NLRP3, classically presenting as neonatal-onset multisystem inflammatory disease [NOMID/CINCA]) (Goldbach-Mansky et al., 2006; Wm et al., 2007), and metabolic disorders (SLC7A7, GBA, and LIPA), as well as malignant processes such as congenital leukemia (Brown et al., 2019; Brown, 2021).