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Idiopathic short stature: will genetics influence the choice between GH and IGF-I therapy?

Endocrinology Centre, William Harvey Research Institute, Queen Mary, University of London, London, EC1M 6BQ UK, ¹ Department of Pediatrics, Oregon Health and Sciences University, Portland, Oregon, 97239-3098 USA and ² Lucile Packard Foundation for Children’s Health, Palo Alto, California, 94304 USA

(Correspondence should be addressed to M O Savage who is now at Department of Endocrinology, John Vane Science Centre, Charterhouse Square, London EC1M 6BQ, UK; Email: m.o.savage{at}qmul.ac.uk)

This paper was presented at the Ipsen symposium, ‘The evolving biology of growth and metabolism’, Lisbon, Portugal, 16–18 March 2007. Ipsen has supported the publication of these proceedings.

Abstract

Background: Idiopathic short stature (ISS) includes a range of conditions. Some are caused by defects in the GH–IGF-I axis. ISS is an approved indication for GH therapy in the USA and a similar approval in Europe may be imminent. Genetic analysis for single-gene defects has made enormous contributions to understanding the physiology of growth regulation. Can this type of investigation help in predicting growth responses to GH or IGF-I therapy?

Methods: The rationale for choice of GH or IGF-I therapy in ISS is reviewed. Many ISS patients have low IGF-I, but most can generate IGF-I levels in response to short-term GH administration. Some GH resistance seems to be present. Mutation analysis in several cohorts of GHIS and ISS patients is reviewed.

Results: Low IGF-I levels suggest either unrecognised GH deficiency or GH resistance. In classical GHIS patients, there was a positive relationship between IGFBP-3 levels and height SDS. No relationship exists between mutations and phenotype. There is a wide variability of phenotype in patients carrying identical mutations. Heterozygous GH receptor (GHR) mutations were present in <5% of ISS patients and their role in causing growth defects is questionable. Exceptions are dominant negative mutations that have been shown to disturb growth.

Conclusions: Analysis for single-gene defects does not give sensitive predictions of phenotype and cannot predict responses to GH or IGF-I therapy. Endocrine abnormalities have closer correlations with phenotype and may thus be a better guide to therapeutic responsiveness.