The most common indications for HCT included SCID (n = 28) in 76% of children, while the remainder (n = 9, 14%) received HCT for various indications including hemophagocytic lymphohistiocytosis, X-linked chronic granulomatous disease, cytotoxic T-lymphocyte-associated protein-4 (CTLA-4) haploinsufficiency, hyperimmunoglobulin M syndrome, signal transducer and activator of transcription 1 (STAT1) gain-of-function (GOF), and 22q11 deletion syndrome. Here, CTLA4 is linked to hemophagocytic syndrome.