Preliminary validation of a prediction model for the short-term growth response to growth hormone therapy in children with idiopathic short stature

Adult height in short children born small for gestational age treated with growth hormone

BACKGROUND AND OBJECTIVE

Recombinant human growth hormone (rhGH) treatment in small for gestational age (SGA) children has been effective, although there is significant variability in the response. Adult height and the factors that determine the long-term response are evaluated.

PATIENTS AND DESIGN

A retrospective study of 80 patients born SGA with short stature treated with rhGH and followed until adult height (23 males).

RESULTS

The group starting treatment pre-puberty reached a higher Adult height (-1.4±0.6 vs. -1.9±.6 in pubertal children), the highest final height gain was achieved in those treated for at least 2years prepuberty (1.32±.5 SDS). Factors associated with greater adult height gain were: a) less height, weight and BMI at start of treatment, b) lower chronological and bone age with lower IGF-I before treatment, c) greater distance to target height, d) higher growth velocity the first and second year of treatment, and higher height gain before and during puberty. The percentage of patients with good response in the first year ranged from 46.6% to 81.6% depending on the criteria. Growth velocity increase ≥3cm/ first year correlated best with long-term response.

CONCLUSION

rhGH treatment in children born SGA produced a varying increase in adult height that allowed them to reach their adult height. The best results occurred in the prepubertal group and did not depend on pituitary GH response.

Identification of factors associated with good response to growth hormone therapy in children with short stature: results from the ANSWER Program®

OBJECTIVE

To identify factors associated with growth in children on growth hormone (GH) therapy using data from the American Norditropin Studies: Web-enabled Research (ANSWER) Program® registry.

METHODS

GH-naïve children with GH deficiency, multiple pituitary hormone deficiency, idiopathic short stature, Turner syndrome, or a history of small for gestational age were eligible (N = 1,002). Using a longitudinal statistical approach, predictive factors were identified in patients with GHD for change from baseline in height standard deviation score (ΔHSDS) following 2 years of treatment.

RESULTS

Gradual increases in ΔHSDS over time were observed for all diagnostic categories. Significant predictive factors of ΔHSDS, ranked by significance were: height velocity (HV) at 4 months > baseline age > baseline HSDS > baseline body mass index (BMI) SDS > baseline insulin-like growth factor I (IGF-I) SDS; gender was not significant. HV at 4 months and baseline BMI SDS were positively correlated, whereas baseline age, HSDS, and IGF-I SDS were negatively correlated with ΔHSDS.

CONCLUSIONS

These results may help guide GH therapy based on pretreatment characteristics and early growth response.

Validation of a Calibrated Prediction Model for Response to Growth Hormone Treatment in an Independent Cohort

BACKGROUND

Prediction models, e.g. for prediction of response to growth hormone treatment, need validation in appropriate independent cohorts, comparing predicted and observed outcomes. In a previous validation of a model for predicting the first-year response to growth hormone treatment in children with idiopathic growth hormone deficiency, overfitting was observed. We modified the prediction formula and now report validation of this modified model.

PATIENTS AND METHODS

The modified and original prediction models were applied to a group of patients selected from Lilly's GeNeSIS database using the same inclusion and exclusion criteria as for the original model. For both prediction methods, observed first-year height velocity was plotted vs. predicted height velocity in a calibration plot. For a valid prediction, the regression line should correspond to the line of identity (observed outcome is equal to predicted outcome); the regression lines for each prediction model were tested for significant differences from this line of identity.

RESULTS

The number of patients fulfilling the criteria was 226. The regression line in the calibration plot of the modified model was not significantly different from the line of identity (p = 0.43), in contrast to the original model (p < 0.001). For the modified model the mean (SD) prediction error was -0.11 (2.05) cm/year and for the original model 0.28 (2.11) cm/year.

CONCLUSION

The modified prediction method, obtained after calibration of the original model, performs well in an independent patient sample and gives more accurate predictions than the original model.