Cystic fibrosis
Tsui became internationally acclaimed in 1989 when he and his team identified the defective gene, namely Cystic fibrosis transmembrane conductance regulator (CFTR), that causes cystic fibrosis, which is a major breakthrough in human genetics. He has also made significant contributions to the study of the human genome, especially the characterization of chromosome 7, and, identification of additional disease genes.