[1] Mayo Clin, Gonda Vasc Ctr, Thrombophilia Ctr, Rochester, MN 55905 USA
[2] Mayo Clin, Dept Hlth Sci Res, Div Biomed Stat & Informat, Rochester, MN USA
[3] Ctr Dis Control & Prevent, Div Blood Disorders MGB, Natl Ctr Birth Defects & Dev Disabil, Atlanta, GA USA