Alu-element insertion in the homeodomain ofHESX1and aplasia of the anterior pituitary

Abstract

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.

A novel HESX1 splice mutation causes isolated GH deficiency by interfering with mRNA processing

“…Referring to the presence of alternative mRNA in normal subjects, a possible explanation to the discordant findings between our data and those obtained by the other authors (19,20) might be the different sources of the RNA used for the RT-PCR. We extracted the mRNA from peripheral blood of the control subjects, whereas Sobrier et al (19,20) extracted the mRNA from Epstein-Barr virus (EBV)-transformed lymphocytes of healthy donor individuals.…”

“…Two HESX1 mutations have previously been reported that interfered with the mRNA processing: an Alu insertion in exon 3 causing the skipping of this exon (19) and the point mutation at position C2 of intron 2 (c.357C2TOC) within the almost invariant dinucleotide of the donor splice site (20) generating two isoforms lacking exon 3 and exons 2-3. Both the mutations abolished the synthesis of the full-length wild-type mRNA in the homozygous patients.…”

“…We extracted the mRNA from peripheral blood of the control subjects, whereas Sobrier et al (19,20) extracted the mRNA from Epstein-Barr virus (EBV)-transformed lymphocytes of healthy donor individuals. It is plausible that the ectopic transcription in the lymphocytes of healthy individuals better reflects the scenario of the healthy developing pituitary gland with respect to the transcription in EBV-transformed lymphocytes.…”

“…To date, 13 mutations in the HESX1 gene have been reported in a broad spectrum of phenotypes ranging from IGHD to CPHD associated in some cases with anomalies such as SOD, pituitary malformations, like ectopy of the neurohypophysis or pituitary aplasia (16)(17)(18)(19)(20)(21)(22). Mutations in HESX1 may be present both at the homozygous (nZ3) and at the heterozygous states (nZ10).…”

Hypothalamic and pituitary development: novel insights into the aetiology

“…The parents were heterozygous for the mutation and phenotypically normal, consistent with an autosomal recessive mode of inheritance. Four additional homozygous mutations have subsequently been identified (Table 1), with phenotypes ranging from evolving hypopituitarism in the absence of midline and eye defects through SOD and pituitary aplasia (27,28). To date, reports of screening patients with sporadic SOD have yielded eight novel heterozygous mutations within HESX1 (Table 2).…”