Yasutomi Nizhizuka was born in Seido Village, Muko–gun (now City of Ashiya), Hyogo–Prefecture, on 12 July 1932, as the second son of Yasunobu and Nobuko Nishizuka. His elder brother, Yasuaki (1922–95, pathologist, President of Aichi Cancer Center), was 10 years old, his eldest sister, Hiroko, was aged 8, his elder sister, Fumiko, was 5, and he was a heterozygotic twin with his sister Junko. His mother, Nobuko, was from the Ijichi family, a huge landlord, which traced its roots back to a powerful family of the Heian Era (eleventh century). When Yasutomi was an infant, he was so weak that his parents were not sure that he would survive to adulthood. He had intussusception (ileus) when he was six months old. He barely survived after emergency surgery at Daido Hospital in Osaka. Since then, he frequently suffered from diseases associated with stomach ache. He was always weak and ailing.