An orphan G-protein-coupled receptor causes human gigantism and/or acromegaly: Molecular biology and clinical correlations

X-linked acrogigantism (X-LAG) is a recently described form of familial or sporadic pituitary gigantism characterized by very early onset GH and IGF-1 excess, accelerated growth velocity, gigantism and/or acromegaloid features. Germline or somatic microduplications of the Xq26.3 chromosomal region, invariably involving the GPR101 gene, constitute the genetic defect leading to X-LAG. GPR101 encodes a class A G protein-coupled receptor that activates the 3′,5′-cyclic adenosine monophosphate signaling pathway. Highly expressed in the central nervous system, the main physiological function and ligand of GPR101 remain unknown, but it seems to play a role in the normal development of the GHRH-GH axis. Early recognition of X-LAG cases is imperative because these patients require clinical management that differs from that of other patients with acromegaly or gigantism. Medical treatment with pegvisomant seems to be the best approach, since X-LAG tumors are resistant to the treatment with somatostatin analogues and dopamine agonists; surgical cure requires near-total hypophysectomy. Currently, the efforts of our research focus on the identification of GPR101 ligands; in addition, the long-term follow-up of X-LAG patients is of extreme interest as this is expected to lead to better understanding of GPR101 effects on human pathophysiology.