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Growth hormone secretion and serum insulin-like growth factor-I concentration in X-linked hypophosphatemic rickets
1Department of Pediatrics, Royal Hospital, Muscat, Oman.
Insights
Children with X-linked hypophosphatemic rickets (HPR) show normal growth hormone (GH) secretion but low insulin-like growth factor-I (IGF-I). Treatment improved linear growth and significantly increased IGF-I levels.
Area of Science:
- Pediatric Endocrinology
- Metabolic Bone Diseases
- Genetics
Background:
- X-linked hypophosphatemic rickets (HPR) is a genetic disorder causing skeletal abnormalities and growth retardation.
- The precise mechanisms underlying growth failure in HPR remain incompletely understood.
- Growth hormone (GH) and insulin-like growth factor-I (IGF-I) axis function is a key determinant of linear growth.
Purpose of the Study:
- To investigate the role of the GH/IGF-I axis in growth retardation associated with HPR.
- To evaluate the impact of standard HPR treatment on GH/IGF-I parameters and linear growth.
- To compare growth and GH/IGF-I dynamics in HPR patients with normal variant short stature (NVSS).
Main Methods:
- Studied seven children with HPR before and after 1+ year of treatment with 1,25-dihydroxyvitaminD3 and phosphate.
- Assessed GH secretion via clonidine provocation test and measured serum IGF-I levels.
- Compared growth velocity (GV) and height standard deviation score (HtSDS) with 20 age-matched NVSS children.
Main Results:
- Children with HPR exhibited normal GH secretion but significantly lower IGF-I levels compared to NVSS controls before treatment.
- HPR treatment led to significant improvements in HtSDS (from -3.9 to -3.05) and GV (from 4.1 to 8.9 cm/year).
- Serum IGF-I concentrations increased significantly from 76.7 ng/ml to 99.6 ng/ml post-treatment in HPR patients.
Conclusions:
- HPR is not characterized by impaired GH secretion.
- Therapeutic intervention in HPR significantly enhances linear growth.
- The improvement in linear growth during HPR treatment is closely associated with a rise in circulating IGF-I levels.
Abstract:
The aetiology of growth retardation in children with X-linked hypophosphatemic rickets (HPR) has not been totally defined. We evaluated growth hormone (GH)/insulin-like growth factor-I (IGF-I) changes in relation to linear growth and biochemical parameters in seven children with X-linked hypophosphatemic rickets before and after treatment with 1,25-dihydroxyvitaminD3 and phosphate therapy for a year or more. Moreover, we compared patients' growth data and GH/IGF-I changes with those for 20 age-matched children with normal variant short stature (NVSS)[with normal GH secretion and height standard deviation score (HtSDS) before -2]. Before treatment, all children with HPR secreted normal GH in response to clonidine provocation (> 10 microgram/l) and their IGF-I concentration was significantly lower than those with NVSS. The HtSDS and growth velocity (GV) of children with HPR improved significantly after (-3.05, 8.9 cm/year, respectively) v. before (-3.9 and 4.1 cm/year, respectively) therapy. Their serum IGF-I concentration increased significantly from 76.7 ng/ml before to 99.6 ng/ml after treatment. In summary children with HPR had no abnormality of GH secretion but improvement of their linear growth was associated with significant increase of circulating IGF-I concentration after treatment.