TAK and GCA are two types of vasculitis characterized by inflammation of the large vessels.
Histologically, both demonstrate granulomatous vasculitis with giant cells. Fewer patients with GCA have been reported in the Japanese literature than in the European and North American literatures. In contrast, more patients with TAK have been reported in Japan than in Europe or the USA [4
]. The point prevalence of GCA in Japan was 690 patients in 1997 (95 % confidence interval [CI] 400–980) [5
]. The prevalence of patients ≥50 years of age was 1.47 cases (95 % CI 0.86–2.10) per 10 million people in Japan compared with 200 and 60 cases per 10 million people in the USA and Spain, respectively [6
The reason for the low incidence of GCA in Japan remains unclear; however, genetic factors affecting the incidence of these diseases are unique and important. The HLA
haplotypes are predominantly (60 %) detected in patients with GCA in America. These haplotypes were less frequently detected in 493 Japanese healthy controls (2.9 and 0.7 %, respectively) than in 60 American healthy controls (15.9 and 3.2 %, respectively) [5
]. This explains why the incidence and/or prevalence of GCA is not high in Japan. Moreover, our study found no significant differences in the clinical features of GCA between Japan and other countries, although GCA cases are less common in Japan than in the USA or Europe [8
TAK, which predominantly affects young females in Japan, affects the aortic arch (Type I), as determined by angiography. The incidence of HLA-B52 (56 %) and HLA-B39 (17 %) was significantly higher in patients with TAK than in healthy controls (25 and 6 %, respectively) in a Japanese study. However, several patients with TAK in India and other East Asian countries are reportedly middle-aged males who express HLA-B39 and exhibit abdominal aorta involvement (Type III).