The terms idiopathic short stature (ISS) and small for gestational age (SGA) were first used in the 1970s and 1980s. ISS described non-syndromic short children with undefined aetiology who did not have growth hormone (GH) deficiency, chromosomal defects, chronic illness, dysmorphic features or low birth weight. Despite originating in the pre-molecular era, ISS is still used as a diagnostic label today. The term SGA was adopted by paediatric endocrinologists to describe children born with low birth weight and/or length, some of whom may experience lack of catch-up growth and present with short stature. GH treatment was approved by the FDA for short children born SGA in 2001, and by the EMA in 2003, and for the treatment of ISS in the US, but not Europe, in 2003. These approvals strengthened the terms SGA and ISS as clinical entities. While clinical and hormonal diagnostic techniques remain important, it is the emergence of genetic investigations that have led to numerous molecular discoveries in both ISS and SGA subjects. The primary message of this article is that the labels ISS and SGA are not definitive diagnoses. We propose that the three disciplines of clinical evaluation, hormonal investigation and genetic sequencing should have equal status in the hierarchy of short stature assessments and should complement each other to identify the true pathogenesis in poorly growing patients.
Robert Rapaport, Jan M Wit, and Martin O Savage
Werner F Blum, Abdullah Alherbish, Afaf Alsagheir, Ahmed El Awwa, Walid Kaplan, Ekaterina Koledova, and Martin O Savage
The growth hormone (GH)–insulin-like growth factor (IGF)-I axis is a key endocrine mechanism regulating linear growth in children. While paediatricians have a good knowledge of GH secretion and assessment, understanding and use of measurements of the components of the IGF system are less current in clinical practice. The physiological function of this axis is to increase the anabolic cellular processes of protein synthesis and mitosis, and reduction of apoptosis, with each being regulated in the appropriate target tissue. Measurement of serum IGF-I and IGF-binding protein (IGFBP)-3 concentrations can complement assessment of GH status in the investigation of short stature and contribute to prediction of growth response during GH therapy. IGF-I monitoring during GH therapy also informs the clinician about adherence and provides a safety reference to avoid over-dosing during long-term management.
Sumana Chatterjee, Emily Cottrell, Stephen J Rose, Talat Mushtaq, Avinaash V Maharaj, Jack Williams, Martin O Savage, Louise A Metherell, and Helen L Storr
The homozygous GH receptor (GHR) pseudoexon (6Ψ) mutation leads to growth hormone insensitivity (GHI) with clinical and biochemical heterogeneity. We investigated whether transcript heterogeneity (6Ψ-GHR to WT-GHR transcript ratio) and/or concurrent defects in other short stature (SS) genes contribute to this.
6Ψ-GHR and WT-GHR mRNA transcripts of four 6Ψ patients (height SDS −4.2 to −3.1) and one control fibroblast were investigated by RT-PCR. Transcripts were quantified by qRT-PCR and delta delta CT analysis and compared using ANOVA with Bonferroni correction. In eleven 6Ψ patients, 40 genes known to cause GHI/SS were analysed by targeted next generation sequencing.
RT-PCR confirmed 6Ψ-GHR transcript in the 6Ψ patients but not in the control. 6Ψ-GHR transcript levels were comparable in patients 1 and 3 but significantly different among all other patients. The mean 6Ψ:WT transcript ratios ranged from 29–71:1 for patients 1–4 and correlated negatively with height SDS (R = −0.85; P < 0.001). Eight deleterious variants in six genes were detected, but the number of gene hits did not correlate with the degree of SS in individual 6Ψ patients.
Variable amounts of 6Ψ- and WT-GHR transcripts were identified in 6Ψ patients but no 6Ψ transcript was present in the control. Higher 6Ψ:WT-GHR transcript ratio correlated with SS severity and may explain the phenotypic variability. Analysis of known SS genes suggested that phenotypic variation is independent of the genetic background. This is the first report of transcript heterogeneity producing a spectrum of clinical phenotypes in different individuals harbouring an identical homozygous genetic mutation.