The growth hormone (GH) secretagogue receptor (GHSR) was cloned as the target of a family of synthetic molecules endowed with GH release properties. As shown recently through in vitro means, this receptor displays a constitutive activity whose clinical relevance is unknown. Although pharmacological studies have demonstrated that its endogenous ligand -ghrelin -stimulates, through the GHSR, GH secretion and appetite, the physiological importance of the GHSR-dependent pathways remains an open question that gives rise to much controversy. We report the identification of a GHSR missense mutation that segregates with short stature within 2 unrelated families. This mutation, which results in decreased cell-surface expression of the receptor, selectively impairs the constitutive activity of the GHSR, while preserving its ability to respond to ghrelin. This first description, to our knowledge, of a functionally significant GHSR mutation, which unveils the critical importance of the GHSR-associated constitutive activity, discloses an unusual pathogenic mechanism of growth failure in humans.

These data, which describe the first case of recessive partial isolated GH deficiency due to GHSR mutations and emphasize the physiological importance of the GHSR in somatic growth, are discussed in light of the dominantly expressed p.A204E mutation.

The pathophysiology of combined pituitary hormone deficiency is just beginning to be elucidated. None of the genes known to be necessary for pituitary development has so far been involved in pituitary gland aplasia in humans. Among these, Hesx1/HESX1, which encodes a homeobox transcription factor, has been shown to be essential for normal forebrain development in mice, and HESX1 mutations in humans have been associated with various pituitary hormone deficiencies usually combined with optic nerve anomalies. Here we have investigated a consanguineous family in which two siblings displayed a complete absence of the anterior pituitary revealed by a deficit in all anterior pituitary hormones. One patient, who also has retinal coloboma, carries a HESX1 defect in the homozygous state: an Alu insertion in exon 3, a sequence that encodes the major part of the homeodomain. The Alu-containing HESX1 allele generates a major transcript lacking this exon, and a minor one in which exons 2 and 3 are skipped, predicting severely truncated proteins. This observation, which combines pituitary aplasia and retinal coloboma, further illustrates the heterogeneity of HESX1-associated disease phenotypes. Anterior pituitary aplasia is a new example of a human disease caused by a germline retrotransposition event involving an Alu sequence.

This study of the first nonconsanguineous patient with LHX3 mutations demonstrates the pleiotropic roles of LHX3 during development and its full involvement in the complex disease phenotype. Isolated limitation of head rotation may exist in heterozygous carriers and would result from a dominant-negative effect. These data allowed the first prenatal diagnoses of this severe condition to be performed.