1. a Department of Biostatistics , St. Jude Children's Research Hospital , Memphis, Tennessee, USA
2. b Department of Human Genetics , University of California , Los Angeles, California, USA
3. d Amgen, Inc. , Thousand Oaks, California
4. e Novartis Pharmaceutical Corporation , East Hanover, New Jersey, USA
5. c Department of Biostatistics , University of California , Los Angeles, California, USA