Prof. Kosaki received his clinical and research training in pediatrics at Keio University in Tokyo and in medical genetics at the University of California, San Diego and Baylor College of Medicine in the U.S. He is board certified in clinical genetics by the American Board of Medical Genetics and Genomics. He is the founding director of the Center for Medical Genetics at Keio University. In 2015, he launched Japan's national program for undiagnosed diseases, the Initiative on Rare and Undiagnosed Diseases, and organized the fifth UDNI conference in Tokyo. He has analyzed more than 5000 undiagnosed patients and their families through WES/WGS and discovered ~10 new diseases, including Kosaki Overgrowth Syndrome and Takenouchi-Kosaki Syndrome, CRMP2-related disorder, CTR-related disorder, NSF-related disorder, and DHX9-related disorder. In 2019, he was elected president of the Japan Society of Human Genetics and president of the Japan Teratology Society. He organized the first pan-Asian human genetics conference, Human Genetics Asia 2023, which was attended by more than 3000 geneticists.