medwireNews: Researchers report that recombinant human growth hormone (r-hGH) can improve growth in children with hypochondroplasia (HCH).

However, Michel Polak (Hôpital Necker Enfants Malades, Paris, France) and colleagues found a wide variation in response. After 3 years of treatment, increases in height relative to an untreated historical cohort ranged from –0.24 to +2.62 standard deviation score (SDS).

They therefore suggest that clinicians compare the response of their individual patients with the average response seen in this study, “and classify each patient as a good or bad responder, and as such decide on the value of continuing r-hGH therapy.”

The study included 19 children aged an average of 9 years who had HCH and a height of –2 SDS or below. None of the patients were GH deficient.

The children were initially treated with an average daily r-hGH dose of 0.057 mg/kg. After adjustment to manage insulin-like growth factor (IGF)-1 levels, the average dose was 0.053 mg/kg.

The researchers note that they “had difficulty maintaining IGF-1 levels below +2 SDS, with one third of the treated patients having at least one IGF-1 measurement more than +2 SDS.”

In particular, they say that three patients who were younger than 5 years at the study start developed very high IGF-1 levels, necessitating an r-hGH reduction from 0.057 to 0.046 mg/kg per day, which resulted in an average IGF-1 level of +1.76 SDS.

“These high values of IGF-1 levels must be related to high r-hGH doses, as they normalized when we reduced to usual r-hGH doses”, the team writes in Hormone Research in Paediatrics.

During the first 3 years of treatment, the 19 patients achieved an average height increase that was +0.62 SDS above that of the general French population and +1.39 SDS higher than that of historical untreated HCH patients.

Height velocity was 5.1 cm/year at baseline, and the children who had entered puberty had done so without any evidence of a growth spurt, as is typical of HCH patients. In the first year of treatment, height velocity increased to 8.1 cm/year; it reduced to 6.2 cm/year in the second year and was not significantly different from baseline in the third year, at 4.8 cm/year.

Seven children reached their adult height during the study, which ranged from 130 to 157 cm for the girls and 164 to 170 cm for the boys. Their average height was –3 SDS relative to the general population, but +1.78 SDS compared with untreated HCH patients. At baseline, their height relative to untreated patients was +0.39, meaning they gained +1.39 SDS, equating to an additional 7.4 cm, but ranging widely, from –1.8 to 19.0 cm.

Children’s response to therapy was not affected by the presence of mutations in the fibroblast growth factor receptor 3 gene, indicating the most severe form of HCH, or by gender. However, there was a correlation with age, such that children who started treatment earlier tended to benefit the most.

By Eleanor McDermid, Senior medwireNews Reporter

Horm Res Paediatr 2014; Advance online publication

Free abstract