Objective C-type natriuretic peptide (CNP) and thyroid hormone (TH) are essential for normal skeletal growth. Plasma CNP peptides correlate with growth velocity, but the relationship between thyroid status and CNP production is unknown. This study examined the impact of restoring normal TH levels on CNP and height velocity (HV) in children with acquired hypo- and hyperthyroidism.
Design We performed a prospective, observational study in prepubertal children with acquired hypothyroidism (n = 15) and hyperthyroidism (n = 12).
Measurements Blood levels of CNP, amino-terminal proCNP (NTproCNP), bone-specific alkaline phosphatase (BSAP), IGF-I and TH levels were measured before and during the first 6 months of standard treatment for hypo- and hyperthyroidism, and correlations were determined.
Results At baseline, HV, CNP, NTproCNP and BSAP were significantly higher in hyper- than in hypothyroid subjects. Changes in TH after treatment were closely coupled to change in CNP and NTproCNP in hyperthyroid, but not in hypothyroid, children. In addition, a positive association of HV with CNP peptides was found during treatment of hyperthyroidism. Normalizing TH did not correlate with changes in BSAP or IGF-I in either group.
Conclusions Plasma CNP peptides are higher in children with hyperthyroidism than in those with hypothyroidism at diagnosis and, in hyperthyroid children, change concordantly with TH and HV during treatment. Differential responses of CNP in the two groups suggest CNP production is dependent on growth plate activity and not a direct effect of TH on CNP gene expression. Our findings suggest novel mechanisms underlying changes in skeletal response during treatment in children with acquired thyroid disease.