Clinical and Genetic Aspects of Behçet's Disease in Japan

Patients with Behçet's disease (BD) suffer from episodic ocular and mucocutaneous attacks, resulting in a reduced quality of life. The phenotype of Japanese BD has been changing over the past 20 years, and the rate of human leukocyte antigen (HLA)-B*51-positive complete type is decreasing while that of intestinal type is increasing. This phenotypical evolution may be related to changes in as-yet-unknown environmental factors, as the immigration influx in Japan is low. Mechanisms discovered by genome-wide association studies include ERAP1-mediated HLA class I antigen bounding pathway, autoinflammation, Th17 cells, natural killer cells, and polarized macrophages, a similar genetic architecture to Crohn's disease, ankylosing spondylitis, and psoriasis. As for treatments, management guidelines have been implemented, and the development of tumor necrosis factor (TNF) inhibitors is markedly improving the outcome of BD, but evidence supporting treatment for special-type BD is limited. The classification of BD into distinct clusters based on clinical manifestations and genetic factors is crucial to the development of optimized medicine.