[1] MRC, Mammalian Genet Unit, Didcot OX11 0RD, Oxon, England
[2] Thomas Jefferson Univ, Jefferson Med Coll, Jefferson Canc Ctr, Dept Microbiol & Immunol, Philadelphia, PA 19107 USA
[3] Univ Nebraska, Dept Anim Sci, Lincoln, NE 68583 USA
[4] Jackson Lab, Bar Harbor, ME 04609 USA
[5] Mt Sinai Hosp, Samuel Lunenfeld Res Inst, Toronto, ON M5G 1X5, Canada
[6] Univ Edinburgh, Western Gen Hosp, Mol Med Ctr, Human Genet Unit, Edinburgh EH4 2XU, Midlothian, Scotland