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Martin O Savage, Cecilia Camacho-Hübner, Alessia David, Louise A Metherell, Vivian Hwa, Ron G Rosenfeld and Adrian J L Clark

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.

Open access

Roberto Salvatori, Serban Radian, Yoan Diekmann, Donato Iacovazzo, Alessia David, Plamena Gabrovska, Giorgia Grassi, Anna-Marie Bussell, Karen Stals, Astrid Weber, Richard Quinton, Elizabeth C Crowne, Valentina Corazzini, Lou Metherell, Tara Kearney, Daniel Du Plessis, Ajay Kumar Sinha, Atik Baborie, Anne-Lise Lecoq, Philippe Chanson, Olaf Ansorge, Sian Ellard, Peter J Trainer, David Balding, Mark G Thomas and Márta Korbonits

Objective

Mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene are associated with pituitary adenoma, acromegaly and gigantism. Identical alleles in unrelated pedigrees could be inherited from a common ancestor or result from recurrent mutation events.

Design and methods

Observational, inferential and experimental study, including: AIP mutation testing; reconstruction of 14 AIP-region (8.3 Mbp) haplotypes; coalescent-based approximate Bayesian estimation of the time to most recent common ancestor (tMRCA) of the derived allele; forward population simulations to estimate current number of allele carriers; proposal of mutation mechanism; protein structure predictions; co-immunoprecipitation and cycloheximide chase experiments.

Results

Nine European-origin, unrelated c.805_825dup-positive pedigrees (four familial, five sporadic from the UK, USA and France) included 16 affected (nine gigantism/four acromegaly/two non-functioning pituitary adenoma patients and one prospectively diagnosed acromegaly patient) and nine unaffected carriers. All pedigrees shared a 2.79 Mbp haploblock around AIP with additional haploblocks privately shared between subsets of the pedigrees, indicating the existence of an evolutionarily recent common ancestor, the ‘English founder’, with an estimated median tMRCA of 47 generations (corresponding to 1175 years) with a confidence interval (9–113 generations, equivalent to 225–2825 years). The mutation occurred in a small tandem repeat region predisposed to slipped strand mispairing. The resulting seven amino-acid duplication disrupts interaction with HSP90 and leads to a marked reduction in protein stability.

Conclusions

The c.805_825dup allele, originating from a common ancestor, associates with a severe clinical phenotype and a high frequency of gigantism. The mutation is likely to be the result of slipped strand mispairing and affects protein–protein interactions and AIP protein stability.