Successful allogeneic hematopoietic stem cell transplantation in a boy with X-linked inhibitor of apoptosis deficiency presenting with hemophagocytic lymphohistiocytosis: A case report

X-linked inhibitor of apoptosis (XIAP) deficiency, also known as X-linked lymphoproliferative syndrome type 2 (XLP2), is a rare inherited primary immunodeficiency resulting from the XIAP (also known as BIRC4) mutation. XIAP deficiency is mainly associated with familial hemophagocytic lymphohistiocytosis (HLH) phenotypes, and genetic testing is crucial in diagnosing this syndrome. Allogeneic hematopoietic stem cell transplantation (HSCT) is currently the only successful strategy for the treatment of this disease; however, a limited number of studies has been published concerning the outcomes of allogeneic HSCT in patients with XIAP deficiency. The present study reported a successful allogeneic HSCT performed to treat XIAP deficiency in a Chinese boy presenting with HLH. Polymerase chain reaction and DNA sequencing were performed to confirm the diagnosis of XIAP deficiency, and allogeneic HSCT was performed. Genetic tests revealed a two-nucleotide deletion (c.1021_1022delAA) in the patient, which was inherited from his mother, and resulted in frameshift mutation and premature stop codon (p.N341fsX348); this is considered to be a disease-causing mutation. The XIAP deficiency patient underwent allogeneic HSCT, receiving busulfan-containing reduced intensity myeloablative conditioning regimen, with a good intermediate follow-up result obtained. Therefore, genetic testing is essential to confirm the diagnosis of XIAP deficiency and detect the carrier of mutation. The present case study may promote the investigation of allogeneic HSCT in patients with XIAP deficiency.