[1] Univ N Carolina, Labs Reprod Biol, Chapel Hill, NC 27599 USA
[2] Mater Misericordiae Childrens Hosp, Dept Pediat Endocrinol, Brisbane, Qld 4101, Australia
[3] Univ N Carolina, Dept Pediat, Chapel Hill, NC 27599 USA
[4] Univ N Carolina, Dept Biochem & Biophys, Chapel Hill, NC 27599 USA