[1] Univ Bern, CH-3001 Bern, Switzerland
[2] Harvard Univ, Broad Inst, Cambridge, MA 02142 USA
[3] MIT, Cambridge, MA 02142 USA
[4] Inst Biomed, Helsinki 00014, Finland
[5] Univ Helsinki, FIN-00014 Helsinki, Finland
[6] Uppsala Univ, S-75124 Uppsala, Sweden