National Human Genome Research Institute, National Institutes of Health, Bethesda, MD, USA. hhuang58@jhu.edu.|National Human Genome Research Institute, National Institutes of Health, Bethesda, MD, USA. hhuang58@jhu.edu.|National Human Genome Research Institute, National Institutes of Health, Bethesda, MD, USA. mullikin@mail.nih.gov.|National Human Genome Research Institute, National Institutes of Health, Bethesda, MD, USA. nhansen@mail.nih.gov.