[1] Univ Groningen, Univ Med Ctr Groningen, Dept Pediat, Groningen, Netherlands
[2] Univ Groningen, Univ Med Ctr Groningen, Dept Endocrinol, Groningen, Netherlands
[3] Univ Groningen, Univ Med Ctr Groningen, Dept Nephrol, Groningen, Netherlands
[4] Karolinska Inst, Div Clin Chem, Dept Lab Med, Stockholm, Sweden
[5] Karolinska Univ Hosp, Karolinska Univ Lab, Clin Chem, Stockholm, Sweden