Takada H, Nomura A, Ishimura M, Ichiyama M, Ohga S, Hara T. NEMO mutation as a cause of familial occurrence of Behçetʼs disease in female patients.Behçetʼs disease is a chronic, relapsing, multisystem inflammatory disease of unknown etiology. Nuclear factor κB (NF-κB) essential modulator (NEMO) that is required for the activation of NF-κB plays an important role in inflammation. To investigate the role of NEMO in the pathogenesis of Behçetʼs disease, we analyzed NEMO gene and its expression pattern in tissues in a family with Behçetʼs disease. We found a heterozygous mutation (1217A> T, D406V) in a 6-year-old girl and her mother. Skewed X-chromosome inactivation was not observed in the peripheral blood mononuclear cells as well as in oral and intestinal mucosa of the patients. Accordingly, there was a significant proportion of peripheral blood monocytes that did not produce sufficient intracellular tumor necrosis factor-α with the stimulation of lipopolysaccharide. Heterozygous NEMO mutation is a cause of familial occurrence of Behçetʼs disease in female patients.