Clinical features of 32 new Japanese cases with autoimmune haemorrha‐philia due to anti‐factor XIII antibodies

Introduction Autoimmune haemophilia‐like disease (or haemorrha‐philia) due to anti‐factor XIII (FXIII; F13 to avoid confusion with FVIII or FXII) antibodies (termed AH13) is a severe bleeding disorder. Although AH13 is thought to be rare, ‘the number of its diagnosed patients’ has recently increased in Japan. However, its prevalence remains unknown. Aim To improve understanding of this disease, we examined and diagnosed 32 ‘new’ Japanese patients with AH13. Methods The presence of antibodies against F13‐A subunit and/or F13‐B subunit was confirmed by using a dot blot test and enzyme‐linked immunosorbent assays. Results Most of our patients had autoantibodies against the F13‐A subunit (88%). A predominance of men (59%) was observed. The mean age and residual F13 activity of our AH13 cohort were 71.7 years and 10.5% of normal, respectively, and 53% of cases were idiopathic. Autoimmune disorders and malignancies were the leading underlying disease (both 16%). Intramuscular and subcutaneous bleeding were the leading symptoms (both 72%). Most of our patients were treated with F13 concentrates (72%) to arrest bleeding and with prednisolone (81%) to eradicate anti‐F13 autoantibodies. Cyclophosphamide and rituximab (both 25%) were also administered. The mortality of AH13 was high (22%), and haemorrhage was the major cause of death (71%). Moreover, 13% of our AH13 patients were diagnosed after haemorrhagic death. Conclusion Physicians/haematologists must raise the awareness of AH13 as a life‐threatening disease. This report represents the only experience of a nationwide survey, and may contribute to a diagnosis on potentially overlooked non‐Japanese AH13 patients in other countries in the world.