北海道大学
Niikawa obtained his medical degree in 1967 from Hokkaido University School of Medicine. After residency in Pediatrics at Hokkaido University Hospital, he worked as a pediatrician in Japan for several years. From 1972 to 1975, Niikawa served as a research associate in the embryology and cytogenetics laboratory at the Department of Gynaecology and Obstetrics in the Cantonal Hospital, Geneva University.