[3] In 2006, his research group identified a single nucleotide polymorphism (SNP) in the ABCC11 gene is the determinant of human earwax type.
[5] 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.
From 1984 to 2007, Niikawa was Professor and Chairman of the Department of Human Genetics at Nagasaki University School of Medicine.
After retiring from the position in Nagasaki and becoming Professor Emeritus in 2007, he became Professor and Director at the Research Institute of Personalized Health Sciences, Health Sciences University of Hokkaido, where he served as President of the university from 2010 to 2016.