[1] Univ Texas, SW Med Sch, Dept Pediat, Dallas, TX 75390 USA
[2] Univ Texas, Dept Biostat, Houston, TX USA
[3] Univ Texas, Dept Internal Med, Houston, TX USA
[4] Indiana Univ, Sch Med, Indianapolis, IN USA
[5] Washington Univ, Dept Pediat, St Louis, MO 63130 USA
[6] Childrens Med Ctr, Cyst Fibrosis Ctr, Dallas, TX 75235 USA
[7] Baylor Coll Med, Dept Pediat, Houston, TX 77030 USA