1. Department of Biostatistics and Center for Statistical Genetics, University of Michigan, Ann Arbor, MI 48109, USA.
2. Department of Genetics, University of North Carolina, Chapel Hill, NC 27599, USA.
3. Genome Technology Branch, National Human Genome Research Institute, Bethesda, MD 20892, USA.
4. Department of Mathematics and Statistics, Calvin College, Grand Rapids, MI 49546, USA.
5. Center for Inherited Disease Research (CIDR), Institute of Genetic Medicine, Johns Hopkins School of Medicine, Baltimore, MD 21224, USA.