YEARLY STEPWISE INCREMENTS OF THE GROWTH-HORMONE DOSE RESULTS IN A BETTER GROWTH-RESPONSE AFTER 4 YEARS IN GIRLS WITH TURNER SYNDROME

To optimize the growth promoting effect of growth hormone (GH), 65 pre viously untreated girls with Turner syndrome (TS), chronological age ( CA) 2-11 yr, were randomized into 3 dosage regimen groups: A, B, and C , with a daily recombinant-human GH dose during 4 study years of 4-4-4 -4, 4-6-6-6, and 4-6-8-8 IU/m(2) b.s. The first GH dosage increase in groups B and C resulted in a significantly higher mean height velocity (HV) compared with constant dose group A. During the third year, when the dose was raised again only in group C, mean HV was significantly higher in groups B and C than in group A, and in group C compared with group B. In year 4 only group C mean HV remained significantly higher than group A. The pattern of change in HSDSCA (Dutch-Swedish-Danish T urner references) was identical; however, in year 4 mean Delta HSDSCA in group B also remained significantly higher than group A. After 4 yr GH treatment, the following was determined. 1) The mean Delta HSDSCA was significantly higher for groups B and C compared with group A, but not significantly different between groups B and C. 2) Although signi ficantly higher compared with estimated values for untreated Dutch gir ls with TS, bone maturation of the GH treated girls was not significan tly different between groups. 3) It was positively related with the de gree of bone age (BA) retardation at start of study and negatively wit h baseline CA. 4) Both the modified Index of Potential Height (mIPH(RU S)) and a recently developed Turner-specific final height (FH) predict ion method (PTSRUS), based on regression coefficients for H, CA, and b one age, showed significant increases in mean FH prediction, without s ignificant differences between groups. PTSRUS values were markedly hig her than the mIPH(RUS) values. Dose dependency could be shown for the area under the curve (AUC) for GH, but Delta HSDSCA was not linearly r elated with AUC. Baseline GH binding protein (BP) levels were in 84% o f the cases within the normal age range; the decrease in mean levels a fter 6 months GH was not significant. Mean insulin-like growth factor I (IGF-I) and IGFBP-3 plasma levels increased significantly, without s ignificant differences between groups. Delta HSDSCA during GH was depe ndent on IGF-I plasma levels at baseline and during the study period, beta-0.002 and beta-0.0004. Thus, a stepwise GH-dosing approach reduce d the ''waning'' effect of the growth response after 4 yr treatment wi thout undue bone maturation. FH prediction was not significantly diffe rent between treatment groups. Irrespective of the GH dose used, initi ation of GH treatment at a younger age was beneficial after 4 yr GH wh en expressed as actual cm gained or as gain in FH prediction, but was not statistically significant when expressed as Delta HSDSCA over the study period.