Can exaggerated response to a GH provocative test identify patients with partial GH insensitivity syndrome?

OBJECTIVES: In the majority of children with short stature, the etiology is unknown. Mutations of the GH receptor (GHR) have been reported in a few children with apparent idiopathic short stature (ISS). These patients had low IGF-I, IGF-binding protein-3 (IGFBP-3) and GH-binding protein (GHBP), but a normal or exaggerated GH response to provocative stimuli, suggestive of partial GH insensitivity (GHI). We attempted to identify children with partial GHI syndrome, based on their response to GH provocative stimuli and other parameters of the GH-IGF-I axis.

SUBJECTS AND METHODS: One hundred and sixty-four pre-pubertal children (97 boys, 67 girls) aged 7.2 (0.5-16.75) years were studied. All had short stature with height <3rd centile. The weight, bone age (BA) and body mass index (BMI) of the subjects, as well as the parents' heights and mid parental height (MPH) were assessed. Basal blood samples were taken for IGF-I, IGFBP-3 and GHBP. All subjects underwent a GH provocative test with either clonidine, arginine or insulin. The subjects were divided into three groups: (A) patients with peak GH concentration <18 mIU/l in two different provocative tests (GH deficiency - GHD, n=33); (B) patients with peak GH between 18.2 and 39.8 mIU/l (normal response, n=78); (C) patients with peak GH >40 mIU/l (exaggerated GH response, n=53).

RESULTS: No significant differences were found in age, height (standard deviation score (SDS)), parental height (SDS) and the difference between chronological age and bone age (DeltaBA) between the groups. Patients with GHD were heavier (P=0.039) and had significantly higher BMI (SDS) (P=0.001) than the other groups. MPH (SDS) was lower in the group of exaggerated responders (P=0.04) compared with the other groups. No significant differences were found between the groups for the biochemical parameters when expressed nominally or in SDS, except for IGFBP-3 (SDS), which was lower in the GHD group (P=0.005). The GHBP levels were not lower in the group of exaggerated GH response to provocative stimuli. Height (SDS) correlated negatively with basal GH values in pooled data of all the subjects (r=-0.358, P<0.0001), in normal responders (r=-0.45, P<0.0001) and in the exaggerated responders (r=-0.341, P<0.0001), but not in the GHD group.

CONCLUSION: Exaggerated GH response to provocative tests alone does not appear to be useful in identifying children with GHI.