Craniofacial growth in growth hormone-deficient rats

Although supplementation with growth hormone (GH) is an accepted treatment for children who are GH-deficient or very small in stature, its effect on the craniofacial skeleton has been little studied. The goal of this study was to compare the absolute and relative growth of the craniofacial skeleton in GH-deficient dwarf rats to that in wild-type rats of the same strain, using a mixed-longitudinal radiographic design. Lateral and dorsoventral X-rays of the head and hindlimb were obtained weekly in dwarf and wild-type female Lewis rats from 4 to 9 weeks of age (n = 14 for each time interval). The X-rays were scanned, 27 cephalometric points were digitized, and selected linear distances were measured between points. Multilevel statistical procedures were used to model growth changes in different regions of the head. Among craniofacial measures, growth curves of the two groups differed greatly in the magnitude of initial size differences and the effect of GH deficiency on growth velocity. Considerable variation (65-97%) also existed among craniofacial measures with regard to relative maturity (i.e., the percentage of growth completed between the first and last time intervals). The deficiency effect (a quantitative estimate of the extent to which growth velocity was affected by GH) was negatively correlated (r = -0.52, P < 0.01) with relative maturity of a particular measure. The dependence of the GH effect on relative maturity suggests that different craniofacial morphologies may result depending on the timing of GH supplementation therapy.