It has long been recognized that growth failure encompasses a diverse spectrum of underlying pathophysiological processes, a characteristic that has significantly impacted both the diagnosis and management of growth disorders. This problem is exacerbated by inherent difficulty in distinguishing the borders between the 'normal range' for stature and defined abnormal growth. Evaluation of GH secretion has proven problematic, both diagnostically and prognostically, except in cases of unequivocal GH deficiency. Measurement of serum concentrations of IGF-I, IGFBP-3, and ALS have proven useful in the assessment of GH responsiveness and have contributed to the concept of primary and secondary 'IGF deficiency'. Nevertheless, there is great need for biochemical and/or molecular biomarkers that could: i) predict short- and long-term responsiveness to various therapeutic modalities, such as GH and IGF-I, and ii) predict potential risk for adverse effects of therapy. Candidate proteins and genes identified to date, and worthy of further evaluation, include IGF-I, IGF-I receptor, GH receptor and its variants (such as exon 3-deleted GHR), STAT5b and short stature homeobox. Proteomic analysis of serum samples pre- and post-treatment and correlation with clinical responsiveness should provide additional candidate biomarkers. Molecular studies to consider include: i) sequencing and mutation analysis of known genetic components of the GH-IGF axis; ii) evaluation of single nucleotide polymorphisms of candidate genes; and iii) identification of new candidate genes. It is proposed that the major target population to study is that of children currently labeled as idiopathic short stature (ISS). These children can be divided into those with: i) primary IGFD, where the focus should be on genes related to GHR, GHR signaling, and IGF-I gene expression, or ii) no IGFD (i.e. 'true ISS'), where the focus should be on genes related to IGFR, IGF signaling and epiphyseal growth.
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