Comment on: 'Metagenome-wide association study of gut microbiome revealed novel aetiology of rheumatoid arthritis in the Japanese population' by Kishikawa et al. Issue 5 (29th May 2020) - Kitamura, Kaori; Shionoya, Hiroshi; Terato, Kuniaki; Suzuki, Suguru; Fukai, Richio; Uda, Shinichi; Abe, Chiyuki; Takemori, Hiromitsu; Nishimura, Keita; Baba, Hisashi; Waritani, Takaki; Katayama, Kou