Hemophilia B in a female with intellectual disability caused by a deletion of Xq26.3q28 encompassing the F9

BACKGROUND: Hemophilia B is an X‐linked recessive disorder caused by mutations in the F9 on Xq27.1. Mainly males are affected but about 20% of female carriers have clotting factor IX activity below 0.40 IU/ml and bleeding problems. Fragile‐X syndrome (FMR1) and FRAXE syndrome (AFF2) are well‐known causes of X‐linked recessive intellectual disability. Simultaneous deletion of both FMR1 and AFF2 in males results in severe intellectual disability. In females the phenotype is more variable. We report a 19‐year‐old female with severe intellectual disability and a long‐standing bleeding history. METHODS: A SNP array analysis (Illumina Human Cyto 12‐SNP genotyping array) and sequencing of F9 were performed. Laboratory tests were performed to evaluate the bleeding diathesis. RESULTS: Our patient was diagnosed with mild hemophilia B after finding an 11 Mb deletion of Xq26.3q28 that included the following genes among others IDS,SOX3,FMR1,AFF2, and F9. CONCLUSION: The case history demonstrates that a severe bleeding tendency suggestive of a hemostasis defect in patients with intellectual disability warrants careful hematological and genetic work‐up even in the absence of a positive family history.