Hemophagocytic lymphohistiocytosis in a female patient due to a heterozygous XIAP mutation and skewed X chromosome inactivation.

Genetic forms of hemophagocytic lymphohistiocytosis (HLH) are caused by mutations in autosomal recessive genes affecting perforin-dependent cytotoxic function and two X-linked genes affecting distinct cell signaling pathways: SH2D1A and XIAP. HLH caused by mutations in X-linked genes is typically found only in males. Here we report the occurrence of HLH in a female caused by a heterozygous mutation in XIAP. Flow cytometric studies confirmed the absence of XIAP protein expression, while an X chromosome inactivation assay revealed an extreme skewing ratio of 99:1. This finding demonstrates that females are susceptible to X-linked forms of HLH through skewed X chromosome inactivation.