Interdisciplinary Program in bioinformatics, Seoul National University, 1 Kwanak-ro Kwanak-gu, Seoul 151-742, Korea, Institute of Human Genetics, University of Bonn, D-53127 Bonn, Germany, Department of Biostatistics, Harvard School of Public Health, 677 Huntington Avenue. Boston, MA 02115, USA, Harvard Medical School, 25 Shattuck St, Boston, MA 02115, USA, Center for Genomic Medicine, Brigham and Womens Hospital, 75 Francis Street, Boston MA 02115, USA, Department of Biostatistics, Harvard School of Public Health, 667 Huntington Ave, Boston, MA 02115, USA, Institute for Genomic Mathematics, University of Bonn, D-53127 Bonn, Germany, German Center for Neurodegenerative Diseases, D-53127 Bonn, Germany, Department of Statistics, Seoul National University 1 Kwanak-ro Kwanak-gu, Seoul 151-742, Korea and Department of Public Health Science, Seoul National University, 1 Kwanak-ro Kwanak-gu, Seoul 151-742, Korea.