Identification and functional analysis of the novel S179R POU1F1 mutation associated with combined pituitary hormone deficiency

POU1F1/Pou1f1 c.143-83A > G Variant Disrupts the Branch Site in Pre-mRNA and Leads to Dwarfism

POU Class 1 Homeobox1 (POU1F1/Pou1f1) is a well-established pituitary-specific transcription factor, and causes, when mutated, combined pituitary hormone deficiency in humans and mice. POU1F1/Pou1f1 has 2 isoforms: the alpha and beta isoforms. Recently, pathogenic variants in the unique coding region of the beta isoform (beta domain) and the intron near the exon-intron boundary for the beta domain were reported, although their functional consequences remain obscure. In this study, we generated mice carrying the Pou1f1 c.143-83A>G substitution that recapitulates the human intronic variant near the exon-intron boundary for the beta domain. Homozygous mice showed postnatal growth failure, with an average body weight that was 35% of wild-type littermates at 12 weeks, which was accompanied by anterior pituitary hypoplasia and deficiency of circulating insulin-like growth factor 1 and thyroxine. The results of RNA-seq analysis of the pituitary gland were consistent with reduction of somatotrophs, and this was confirmed immunohistochemically. Reverse transcription polymerase chain reaction of pituitary Pou1f1 mRNA showed abnormal splicing in homozygous mice, with a decrease in the alpha isoform, an increase in the beta isoform, and the emergence of the exon-skipped transcript. We further characterized artificial variants in or near the beta domain, which were candidate positions of the branch site in pre-mRNA, using cultured cell-basis analysis and found that only c.143-83A>G produced transcripts similar to the mice model. Our report is the first to show that the c.143-83A>G variant leads to splicing disruption and causes morphological and functional abnormalities in the pituitary gland. Furthermore, our mice will contribute understanding the role of POU1F1/Pou1f1 transcripts in pituitary development.

Congenital hypopituitarism due to novel compound heterozygous POU1F1 gene mutation: A case report and review of the literature

Failure to thrive is one of the most common complaints in the endocrinology and genetics clinic. An 8-month-old girl with presentation of motor developmental delay, failure to thrive, and midline facial defects, with history of hypoglycemia at birth and central congenital hypothyroidism (CCH), was brought to our genetic clinic. Hormone test demonstrated combined pituitary hormone deficiency with growth hormone deficiency (GHD), central hypothyroidism, and hypoprolactinemia. Brain magnetic resonance imaging (MRI) showed anterior pituitary hypoplasia (APH), abnormal pituitary stalk, and preserved posterior pituitary lobe. Whole exome sequence (WES) identified a compound heterozygous mutation of the POU1F1 gene: c.649C>T (p.Arg217Ter) and c.662T>C (p.Ile221Thr), which are de novo mutation and inherited from mother, respectively. The patient's phenotype was consistent clinically with congenital hypopituitarism due to the POU1F1 gene mutation. Based on our literature review, this is the first report of the c.662T>C mutation, to the best of our knowledge. Our study demonstrates the power of WES for early diagnosis of congenital hypopituitarism with its relative phenotype for improving prognosis and preventing irreversible deficit.

Heterozygous LHX3 mutations may lead to a mild phenotype of combined pituitary hormone deficiency

LHX3 is an LIM domain transcription factor involved in the early steps of pituitary ontogenesis. We report here functional studies of three allelic variants, including the first heterozygous variant of LHX3 NM_178138.5(LHX3):c.587T>C (p.(Leu196Pro)) that may be responsible for a milder phenotype of hypopituitarism. Our functional studies showed that NM_178138.5(LHX3):c.587T>C (p.(Leu196Pro)) was not able to activate target promoters in vitro, as it did not bind DNA, and likely affected LHX3 function via a mechanism of haplo-insufficiency. Our study demonstrates the possibility that patients with a heterozygous variant of LHX3 may have pituitary deficiencies, with a milder phenotype than patients with homozygous variants. It is thus of vital to propose an optimal follow-up of such patients, who, until now, were considered as not being at risk of presenting pituitary deficiency. The second variant NM_178138.5(LHX3):c.622C>G (p.(Arg208Gly)), present in a homozygous state, displayed decreased transactivating ability without loss of binding capacity in vitro, concordant with in silico analysis; it should thus be considered to affect LHX3 function. In contrast, the NM_178138.5(LHX3):c.929G>C (p.(Arg310Pro)) variant, in a heterozygous state, also predicted as deleterious in silico, proved functionally active in vitro, and should thus still be classified as a variant of unknown significance. Our study emphasizes the need for functional studies due to the limits of software-based predictions of new variants, and the possible association of a pituitary phenotype to heterozygous LHX3 variants.

Rare diseases in clinical endocrinology: a taxonomic classification system

PURPOSE

Rare endocrine-metabolic diseases (REMD) represent an important area in the field of medicine and pharmacology. The rare diseases of interest to endocrinologists involve all fields of endocrinology, including rare diseases of the pituitary, thyroid and adrenal glands, paraganglia, ovary and testis, disorders of bone and mineral metabolism, energy and lipid metabolism, water metabolism, and syndromes with possible involvement of multiple endocrine glands, and neuroendocrine tumors. Taking advantage of the constitution of a study group on REMD within the Italian Society of Endocrinology, consisting of basic and clinical scientists, a document on the taxonomy of REMD has been produced.

METHODS AND RESULTS

This document has been designed to include mainly REMD manifesting or persisting into adulthood. The taxonomy of REMD of the adult comprises a total of 166 main disorders, 338 including all variants and subtypes, described into 11 tables.

CONCLUSIONS

This report provides a complete taxonomy to classify REMD of the adult. In the future, the creation of registries of rare endocrine diseases to collect data on cohorts of patients and the development of common and standardized diagnostic and therapeutic pathways for each rare endocrine disease is advisable. This will help planning and performing intervention studies in larger groups of patients to prove the efficacy, effectiveness, and safety of a specific treatment.

Two novel mutations in the POU1F1 gene generate null alleles through different mechanisms leading to combined pituitary hormone deficiency

BACKGROUND

  Mutations in the POU1F1 gene severely affect the development and function of the anterior pituitary gland and lead to combined pituitary hormone deficiency (CPHD).

OBJECTIVE

  The clinical and genetic analysis of a patient presenting with CPHD and functional characterization of identified mutations.

PATIENT

  We describe a male patient with extreme short stature, learning difficulties, anterior pituitary hypoplasia, secondary hypothyroidism and undetectable prolactin, growth hormone (GH) and insulin-like growth factor 1 (IGF1), with normal random cortisol.

DESIGN

  The POU1F1 coding region was amplified by PCR and sequenced; the functional consequence of the mutations was analysed by cell transfection and in vitro assays.

RESULTS

  Genetic analysis revealed compound heterozygosity for two novel putative loss of function mutations in POU1F1: a transition at position +3 of intron 1 [IVS1+3nt(A>G)] and a point mutation in exon 6 resulting in a substitution of arginine by tryptophan (R265W). Functional analysis revealed that IVS1+3nt(A>G) results in a reduction in the correctly spliced POU1F1 mRNA, which could be corrected by mutations of the +4, +5 and +6 nucleotides. Analysis of POU1F1(R265W) revealed complete loss of function resulting from severely reduced protein stability.

CONCLUSIONS

  Combined pituitary hormone deficiency in this patient is caused by loss of POU1F1 function by two novel mechanisms, namely aberrant splicing (IVS1+3nt (A>G) and protein instability (R265W). Identification of the genetic basis of CPHD enabled the cessation of hydrocortisone therapy without the need for further assessment for evolving endocrinopathy.

The use of neuroimaging for assessing disorders of pituitary development

Magnetic resonance imaging (MRI) is the radiological examination method of choice for evaluating hypothalamo-pituitary-related endocrine disease and is considered essential in the assessment of patients with suspected hypothalamo-pituitary pathology. Physicians involved in the care of such patients have, in MRI, a valuable tool that can aid them in determining the pathogenesis of their patients' underlying pituitary conditions. Indeed, the use of MRI has led to an enormous increase in our knowledge of pituitary morphology, improving, in particular, the differential diagnosis of hypopituitarism. Specifically, MRI allows detailed and precise anatomical study of the pituitary gland by differentiating between the anterior and posterior pituitary lobes. MRI recognition of pituitary hyperintensity in the posterior part of the sella, now considered a marker of neurohypophyseal functional integrity, has been the most striking finding in the diagnosis and understanding of certain forms of 'idiopathic' and permanent growth hormone deficiency (GHD). Published data show a number of correlations between pituitary abnormalities as observed on MRI and a patient's endocrine profile. Indeed, several trends have emerged and have been confirmed: (i) a normal MRI or anterior pituitary hypoplasia generally indicates isolated growth hormone deficiency that is mostly transient and resolves upon adult height achievement; (ii) patients with multiple pituitary hormone deficiencies (MPHD) seldom show a normal pituitary gland; and (iii) the classic triad of ectopic posterior pituitary, pituitary stalk hypoplasia/agenesis and anterior pituitary hypoplasia is more frequently reported in MPHD patients and is generally associated with permanent GHD. Pituitary abnormalities have also been reported in patients with hypopituitarism carrying mutations in several genes encoding transcription factors. Establishing endocrine and MRI phenotypes is extremely useful for the selection and management of patients with hypopituitarism, both in terms of possible genetic counselling and in the early diagnosis of evolving anterior pituitary hormone deficiencies. Going forward, neuroimaging techniques are expected to progressively expand and improve our knowledge and understanding of pituitary diseases.

Pituitary transcription factors in the aetiology of combined pituitary hormone deficiency

The somatotropic axis is the central postnatal regulator of longitudinal growth. One of its major components--growth hormone--is produced by the anterior lobe of the pituitary, which also expresses and secretes five additional hormones (prolactin, thyroid stimulating hormone, follicle stimulating hormone, luteinizing hormone, adrenocorticotropic hormone). Proper development of the pituitary assures the regulation of critical processes such as metabolic control, puberty and reproduction, stress response and lactation. Ontogeny of the adenohypophysis is orchestrated by inputs from neighbouring tissues, cellular signalling molecules and transcription factors. Perturbation of expression or function of these factors has been implicated in the aetiology of combined pituitary hormone deficiency (CPHD). Mutations within the genes encoding for the transcription factors LHX3, LHX4, PROP1, and POU1F1 (PIT1) that act at different stages of pituitary development result in unique patterns of hormonal deficiencies reflecting their differential expression during organogenesis. In the case of LHX3 and LHX4 the phenotype may include extra-pituitary manifestations due to the function of these genes/proteins outside the pituitary gland. The remarkable variability in the clinical presentation of affected patients indicates the influence of the genetic background, environmental factors and possibly stochastic events. However, in the majority of CPHD cases the aetiology of this heterogeneous disease remains unexplained, which further suggests the involvement of additional genes. Identification of these factors might also help to close the gaps in our understanding of pituitary development, maintenance and function.

Genetic regulation of pituitary gland development in human and mouse

Normal hypothalamopituitary development is closely related to that of the forebrain and is dependent upon a complex genetic cascade of transcription factors and signaling molecules that may be either intrinsic or extrinsic to the developing Rathke's pouch. These factors dictate organ commitment, cell differentiation, and cell proliferation within the anterior pituitary. Abnormalities in these processes are associated with congenital hypopituitarism, a spectrum of disorders that includes syndromic disorders such as septo-optic dysplasia, combined pituitary hormone deficiencies, and isolated hormone deficiencies, of which the commonest is GH deficiency. The highly variable clinical phenotypes can now in part be explained due to research performed over the last 20 yr, based mainly on naturally occurring and transgenic animal models. Mutations in genes encoding both signaling molecules and transcription factors have been implicated in the etiology of hypopituitarism, with or without other syndromic features, in mice and humans. To date, mutations in known genes account for a small proportion of cases of hypopituitarism in humans. However, these mutations have led to a greater understanding of the genetic interactions that lead to normal pituitary development. This review attempts to describe the complexity of pituitary development in the rodent, with particular emphasis on those factors that, when mutated, are associated with hypopituitarism in humans.

Basic science and clinical research advances in the pituitary transcription factors: Pit-1 and Prop-1

PURPOSE OF REVIEW

The pituitary-specific transcription factors, Pit-1 (also called Pou1f1) and prophet of Pit-1 (Prop-1), are critical for normal pituitary development and function. The aim of the present review is to highlight the recent basic science and clinical research advances in these transcription factors, as they relate to signaling pathway interactions, gene regulation, and mutations in human diseases.

RECENT FINDINGS

A number of important basic research discoveries have been made in the area of the pituitary-specific transcription factors, Pit-1 and Prop-1. Among these findings include: the effects of the Pit-1 coactivators, GATA-2 and TRAP-220, on the transcriptional regulation of the TSHbeta gene and thyrotropin expression, characterization of a novel pituitary regulator of Pit-1 expression, Atbf1, elucidation of the roles of Wnt and Notch signaling on Prop-1-mediated specification of the Pit-1 cell lineage and gonadotropes, and the identification of regulatory regions of the Prop-1 gene. Advances in clinical research include: the identification of novel mutations in the human POU1F1 and PROP-1 genes, and screening guidelines for patients with combined pituitary hormone deficiencies and possible mutations in these transcription factors.

SUMMARY

Research into the complex interplay of signaling pathways and transcription factors that regulate the pituitary gland are important areas of developmental biology and normal physiology. Clinically, such research has important implications for human diseases by identifying inheritable transcription factor mutations that may cause pituitary hormonal deficiencies.