Novel HESX1 mutations associated with a life-threatening neonatal phenotype, pituitary aplasia, but normally located posterior pituitary and no optic nerve abnormalities

Common and uncommon mouse models of growth hormone deficiency

Mouse models of growth hormone deficiency (GHD) have provided important tools for uncovering the various actions of GH. Nearly 100 years of research using these mouse lines has greatly enhanced our knowledge of the GH/IGF-1 axis. Some of the shared phenotypes of the five "common" mouse models of GHD include reduced body size, delayed sexual maturation, decreased fertility, reduced muscle mass, increased adiposity, and enhanced insulin sensitivity. Since these common mouse lines outlive their normal-sized littermates - and have protection from age-associated disease - they have become important fixtures in the aging field. On the other hand, the twelve "uncommon" mouse models of GHD described herein have tremendously divergent health outcomes ranging from beneficial aging phenotypes (similar to those described for the common models) to extremely detrimental features (such as improper development of the CNS, numerous sensory organ defects, and embryonic lethality). Moreover, advancements in next generation sequencing technologies have led to the identification of an expanding array of genes that are recognized as causative agents to numerous rare syndromes with concomitant GHD. Accordingly, this review provides researchers with a comprehensive up-to-date collection of the common and uncommon mouse models of GHD that have been used to study various aspects of physiology and metabolism associated with multiple forms of GHD. For each mouse line presented, the closest comparable human syndromes are discussed providing important parallels to the clinic.

Diagnosis of GH Deficiency Without GH Stimulation Tests

Growth hormone deficiency (GHD) is the most commonly affected pituitary hormone in childhood with a prevalence of 1 in 4000-10000 live births. GH stimulation testing (GHST) is commonly used in the diagnostic workup of GHD. However, GHD can be diagnosed in some clinical conditions without the need of GHST. The diagnosis of GHD in newborns does not require stimulation testing. Likewise infants/children with delayed growth and/or short stature associated with neuroradiological abnormalities and one or more additional pituitary hormone deficiencies may not need GHST. This review summarizes the current evidence on the diagnosis of GHD without stimulation tests.

Advances in differential diagnosis and management of growth hormone deficiency in children

Growth hormone (GH) deficiency (GHD) in children is defined as impaired production of GH by the pituitary gland that results in growth failure. This disease might be congenital or acquired, and occurs in isolation or in the setting of multiple pituitary hormone deficiency. Isolated GHD has an estimated prevalence of 1 patient per 4000-10,000 live births and can be due to multiple causes, some of which are yet to be determined. Establishing the correct diagnosis remains key in children with short stature, as initiating treatment with recombinant human GH can help them attain their genetically determined adult height. During the past two decades, our understanding of the benefits of continuing GH therapy throughout the transition period from childhood to adulthood has increased. Improvements in transitional care will help alleviate the consequent physical and psychological problems that can arise from adult GHD, although the consequences of a lack of hormone replacement are less severe in adults than in children. In this Review, we discuss the differential diagnosis in children with GHD, including details of clinical presentation, neuroimaging and genetic testing. Furthermore, we highlight advances and issues in the management of GHD, including details of transitional care.

Pituitary stalk interruption syndrome

Pituitary stalk interruption syndrome (PSIS) is a distinct developmental defect of the pituitary gland identified by magnetic resonance imaging and characterized by a thin, interrupted, attenuated or absent pituitary stalk, hypoplasia or aplasia of the adenohypophysis, and an ectopic posterior pituitary. The precise etiology of PSIS still remains elusive or incompletely confirmed in most cases. Adverse perinatal events, including breech delivery and hypoxia, were initially proposed as the underlying mechanism affecting the hypothalamic-pituitary axis. Nevertheless, recent findings have uncovered a wide variety of PSIS-associated molecular defects in genes involved in pituitary development, holoprosencephaly (HPE), neural development, and other important cellular processes such as cilia function. The application of whole exome sequencing (WES) in relatively large cohorts has identified an expanded pool of potential candidate genes, mostly related to the Wnt, Notch, and sonic hedgehog signaling pathways that regulate pituitary growth and development during embryogenesis. Importantly, WES has revealed coexisting pathogenic variants in a significant number of patients; therefore, pointing to a multigenic origin and inheritance pattern of PSIS. The disorder is characterized by inter- and intrafamilial variability and incomplete or variable penetrance. Overall, PSIS is currently viewed as a mild form of an expanded HPE spectrum. The wide and complex clinical manifestations include evolving pituitary hormone deficiencies (with variable timing of onset and progression) and extrapituitary malformations. Severe and life-threatening symptomatology is observed in a subset of patients with complete pituitary hormone deficiency during the neonatal period. Nevertheless, most patients are referred later in childhood for growth retardation. Prompt and appropriate hormone substitution therapy constitutes the cornerstone of treatment. Further studies are needed to uncover the etiopathogenesis of PSIS.

Analysis of gene variants in the GASH/Sal model of epilepsy

Epilepsy is a complex neurological disorder characterized by sudden and recurrent seizures, which are caused by various factors, including genetic abnormalities. Several animal models of epilepsy mimic the different symptoms of this disorder. In particular, the genetic audiogenic seizure hamster from Salamanca (GASH/Sal) animals exhibit sound-induced seizures similar to the generalized tonic seizures observed in epileptic patients. However, the genetic alterations underlying the audiogenic seizure susceptibility of the GASH/Sal model remain unknown. In addition, gene variations in the GASH/Sal might have a close resemblance with those described in humans with epilepsy, which is a prerequisite for any new preclinical studies that target genetic abnormalities. Here, we performed whole exome sequencing (WES) in GASH/Sal animals and their corresponding controls to identify and characterize the mutational landscape of the GASH/Sal strain. After filtering the results, moderate- and high-impact variants were validated by Sanger sequencing, assessing the possible impact of the mutations by “in silico” reconstruction of the encoded proteins and analyzing their corresponding biological pathways. Lastly, we quantified gene expression levels by RT-qPCR. In the GASH/Sal model, WES showed the presence of 342 variations, in which 21 were classified as high-impact mutations. After a full bioinformatics analysis to highlight the high quality and reliable variants, the presence of 3 high-impact and 15 moderate-impact variants were identified. Gene expression analysis of the high-impact variants of Asb14 (ankyrin repeat and SOCS Box Containing 14), Msh3 (MutS Homolog 3) and Arhgef38 (Rho Guanine Nucleotide Exchange Factor 38) genes showed a higher expression in the GASH/Sal than in control hamsters. In silico analysis of the functional consequences indicated that those mutations in the three encoded proteins would have severe functional alterations. By functional analysis of the variants, we detected 44 significantly enriched pathways, including the glutamatergic synapse pathway. The data show three high-impact mutations with a major impact on the function of the proteins encoded by these genes, although no mutation in these three genes has been associated with some type of epilepsy until now. Furthermore, GASH/Sal animals also showed gene variants associated with different types of epilepsy that has been extensively documented, as well as mutations in other genes that encode proteins with functions related to neuronal excitability, which could be implied in the phenotype of the GASH/Sal. Our findings provide valuable genetic and biological pathway data associated to the genetic burden of the audiogenic seizure susceptibility and reinforce the need to validate the role of each key mutation in the phenotype of the GASH/Sal model.

Development of the Pituitary Gland

The development of the anterior pituitary gland occurs in distinct sequential developmental steps, leading to the formation of a complex organ containing five different cell types secreting six different hormones. During this process, the temporal and spatial expression of a cascade of signaling molecules and transcription factors plays a crucial role in organ commitment, cell proliferation, patterning, and terminal differentiation. The morphogenesis of the gland and the emergence of distinct cell types from a common primordium are governed by complex regulatory networks involving transcription factors and signaling molecules that may be either intrinsic to the developing pituitary or extrinsic, originating from the ventral diencephalon, the oral ectoderm, and the surrounding mesenchyme. Endocrine cells of the pituitary gland are organized into structural and functional networks that contribute to the coordinated response of endocrine cells to stimuli; these cellular networks are formed during embryonic development and are maintained or may be modified in adulthood, contributing to the plasticity of the gland. Abnormalities in any of the steps of pituitary development may lead to congenital hypopituitarism that includes a spectrum of disorders from isolated to combined hormone deficiencies including syndromic disorders such as septo-optic dysplasia. Over the past decade, the acceleration of next-generation sequencing has allowed for rapid analysis of the patient genome to identify novel mutations and novel candidate genes associated with hypothalmo-pituitary development. Subsequent functional analysis using patient fibroblast cells, and the generation of stem cells derived from patient cells, is fast replacing the need for animal models while providing a more physiologically relevant characterization of novel mutations. Furthermore, CRISPR-Cas9 as the method for gene editing is replacing previous laborious and time-consuming gene editing methods that were commonly used, thus yielding knockout cell lines in a fraction of the time. © 2020 American Physiological Society. Compr Physiol 10:389-413, 2020.

Combined Pituitary Hormone Deficiency Caused by a Synonymous HESX1 Gene Mutation

CONTEXT

Mutations in the HESX1 gene can give rise to complex phenotypes that involve variable pituitary hormone deficiencies and other developmental defects.

CASE DESCRIPTION

A 14-year-old boy presented with short stature and delayed puberty and received a diagnosis of GH deficiency, central hypothyroidism, hypogonadotropic hypogonadism, and secondary adrenal insufficiency. He had anterior pituitary hypoplasia, ectopic posterior pituitary, and an interrupted pituitary stalk. Genetic studies uncovered a heterozygous variant in exon 2 of the HESX1 gene (c.219C>T; p.Ser73Ser). This single base change was predicted to be synonymous at the translational level but was shown to cause skipping of exon 2 in the RNA transcript.

CONCLUSIONS

This study of a patient with combined pituitary hormone deficiency revealed an unusual synonymous mutation of the HESX1 gene leading to abnormal RNA processing and indicates the importance of investigating silent variants that at first glance appear to be benign.

First estimate of the scale of canonical 5' splice site GT>GC variants capable of generating wild-type transcripts

It has long been known that canonical 5' splice site (5'SS) GT>GC variants may be compatible with normal splicing. However, to date, the actual scale of canonical 5'SSs capable of generating wild-type transcripts in the case of GT>GC substitutions remains unknown. Herein, combining data derived from a meta-analysis of 45 human disease-causing 5'SS GT>GC variants and a cell culture-based full-length gene splicing assay of 103 5'SS GT>GC substitutions, we estimate that ~15-18% of canonical GT 5'SSs retain their capacity to generate between 1% and 84% normal transcripts when GT is substituted by GC. We further demonstrate that the canonical 5'SSs in which substitution of GT by GC-generated normal transcripts exhibit stronger complementarity to the 5' end of U1 snRNA than those sites whose substitutions of GT by GC did not lead to the generation of normal transcripts. We also observed a correlation between the generation of wild-type transcripts and a milder than expected clinical phenotype but found that none of the available splicing prediction tools were capable of reliably distinguishing 5'SS GT>GC variants that generated wild-type transcripts from those that did not. Our findings imply that 5'SS GT>GC variants in human disease genes may not invariably be pathogenic.

Translating genomics to the clinical diagnosis of disorders/differences of sex development

The medical and psychosocial challenges faced by patients living with Disorders/Differences of Sex Development (DSD) and their families can be alleviated by a rapid and accurate diagnostic process. Clinical diagnosis of DSD is limited by a lack of standardization of anatomical and endocrine phenotyping and genetic testing, as well as poor genotype/phenotype correlation. Historically, DSD genes have been identified through positional cloning of disease-associated variants segregating in families and validation of candidates in animal and in vitro modeling of variant pathogenicity. Owing to the complexity of conditions grouped under DSD, genome-wide scanning methods are better suited for identifying disease causing gene variant(s) and providing a clinical diagnosis. Here, we review a number of established genomic tools (karyotyping, chromosomal microarrays and exome sequencing) used in clinic for DSD diagnosis, as well as emerging genomic technologies such as whole-genome (short-read) sequencing, long-read sequencing, and optical mapping used for novel DSD gene discovery. These, together with gene expression and epigenetic studies can potentiate the clinical diagnosis of DSD diagnostic rates and enhance the outcomes for patients and families.

Pituitary Transcription Factor Mutations Leading to Hypopituitarism

Congenital pituitary hormone deficiency is a disabling condition. It is part of a spectrum of disorders including craniofacial midline developmental defects ranging from holoprosencephaly through septo-optic dysplasia to combined and isolated pituitary hormone deficiency. The first genes discovered in the human disease were based on mouse models of dwarfism due to mutations in transcription factor genes. High-throughput DNA sequencing technologies enabled clinicians and researchers to find novel genetic causes of hypopituitarism for the more than three quarters of patients without a known genetic diagnosis to date. Transcription factor (TF) genes are at the forefront of the functional analysis of novel variants of unknown significance due to the relative ease in in vitro testing in a research lab. Genetic testing in hypopituitarism is of high importance to the individual and their family to predict phenotype composition, disease progression and to avoid life-threatening complications such as secondary adrenal insufficiency.This chapter aims to highlight our current understanding about (1) the contribution of TF genes to pituitary development (2) the diversity of inheritance and phenotype features in combined and select isolated pituitary hormone deficiency and (3) provide an initial assessment on how to approach variants of unknown significance in human hypopituitarism. Our better understanding on how transcription factor gene variants lead to hypopituitarism is a meaningful step to plan advanced therapies to specific genetic changes in the future.

The origins of the circumventricular organs

The circumventricular organs (CVOs) are specialised neuroepithelial structures found in the midline of the brain, grouped around the third and fourth ventricles. They mediate the communication between the brain and the periphery by performing sensory and secretory roles, facilitated by increased vascularisation and the absence of a blood-brain barrier. Surprisingly little is known about the origins of the CVOs (both developmental and evolutionary), but their functional and organisational similarities raise the question of the extent of their relationship. Here, I review our current knowledge of the embryonic development of the seven major CVOs (area postrema, median eminence, neurohypophysis, organum vasculosum of the lamina terminalis, pineal organ, subcommissural organ, subfornical organ) in embryos of different vertebrate species. Although there are conspicuous similarities between subsets of CVOs, no unifying feature characteristic of their development has been identified. Cross-species comparisons suggest that CVOs also display a high degree of evolutionary flexibility. Thus, the term 'CVO' is merely a functional definition, and features shared by multiple CVOs may be the result of homoplasy rather than ontogenetic or phylogenetic relationships.

Transcriptome analysis reveals determinant stages controlling human embryonic stem cell commitment to neuronal cells

Proper neural commitment is essential for ensuring the appropriate development of the human brain and for preventing neurodevelopmental diseases such as autism spectrum disorders, schizophrenia, and intellectual disorders. However, the molecular mechanisms underlying the neural commitment in humans remain elusive. Here, we report the establishment of a neural differentiation system based on human embryonic stem cells (hESCs) and on comprehensive RNA sequencing analysis of transcriptome dynamics during early hESC differentiation. Using weighted gene co-expression network analysis, we reveal that the hESC neurodevelopmental trajectory has five stages: pluripotency (day 0); differentiation initiation (days 2, 4, and 6); neural commitment (days 8-10); neural progenitor cell proliferation (days 12, 14, and 16); and neuronal differentiation (days 18, 20, and 22). These stages were characterized by unique module genes, which may recapitulate the early human cortical development. Moreover, a comparison of our RNA-sequencing data with several other transcriptome profiling datasets from mice and humans indicated that Module 3 associated with the day 8-10 stage is a critical window of fate switch from the pluripotency to the neural lineage. Interestingly, at this stage, no key extrinsic signals were activated. In contrast, using CRISPR/Cas9-mediated gene knockouts, we also found that intrinsic hub transcription factors, including the schizophrenia-associated SIX3 gene and septo-optic dysplasia-related HESX1 gene, are required to program hESC neural determination. Our results improve the understanding of the mechanism of neural commitment in the human brain and may help elucidate the etiology of human mental disorders and advance therapies for managing these conditions.

A newborn with combined pituitary hormone deficiency developing shock and sludge

A male neonate was born at 41 weeks of gestation with a birth weight of 3320 g. Artificial respiratory management was required due to respiratory disturbance 1 h after birth, and subsequently catecholamine-refractory low cardiac output-induced shock occurred. Severe combined pituitary hormone deficiency (CPHD) was considered based on the presence of his respiratory disturbance, hypoglycemia and micropenis. After hydrocortisone (HDC) administration, circulatory dynamics rapidly improved. Brain magnetic resonance imaging (MRI) showed aplasia of the anterior pituitary gland and ectopic posterior gland. γ-Glutamyltranspeptidase (γ-GTP) increased from day 10 after birth and direct bilirubin increased from day 18. On ultrasonography, sludge filling the common bile duct and gall bladder was observed. After initiating treatment with both ursodeoxycholic acid and recombinant human growth hormone (rhGH), cholestasis improved and the sludge disappeared at 3 months after birth. In newborns with CPHD, severe central adrenal insufficiency might induce cardiogenic shock after birth. Early diagnosis and intervention are necessary.

Classical and non-classical causes of GH deficiency in the paediatric age

Growth hormone deficiency (GHD) may result from a failure of hypothalamic GHRH production or release, from congenital disorders of pituitary development, or from central nervous system insults including tumors, surgery, trauma, radiation or infiltration from inflammatory diseases. Idiopathic, isolated GHD is the most common sporadic form of hypopituitarism. GHD may also occur in combination with other pituitary hormone deficiencies, and is often referred to as hypopituitarism, combined pituitary hormone deficiency (CPHD), multiple pituitary hormone deficiency (MPHD) or panhypopituitarism. Children without any identifiable cause of their GHD are commonly labeled as having idiopathic hypopituitarism. MRI imaging is the technique of choice in the diagnosis of children with hypopituitarism. Marked differences in MRI pituitary gland morphology suggest different etiologies of GHD and different prognoses. Pituitary stalk agenesis and ectopic posterior pituitary (EPP) are specific markers of permanent GHD, and patients with these MRI findings show a different clinical and endocrine outcome compared to those with normal pituitary anatomy or hypoplastic pituitary alone. Furthermore, the classic triad of ectopic posterior pituitary gland, pituitary stalk hypoplasia/agenesis, and anterior pituitary gland hypoplasia is generally associated with permanent GHD. T2 DRIVE images aid in the identification of pituitary stalk without the use of contrast medium administration. Future developments in imaging techniques will undoubtedly reveal additional insights. Mutations in a number of genes encoding transcription factors - such as HESX1, SOX2, SOX3, LHX3, LHX4, PROP1, POU1F1, PITX, GLI3, GLI2, OTX2, ARNT2, IGSF1, FGF8, FGFR1, PROKR2, PROK2, CHD7, WDR11, NFKB2, PAX6, TCF7L1, IFT72, GPR161 and CDON - have been associated with pituitary dysfunction and abnormal pituitary gland development; the correlation of genetic mutations to endocrine and MRI phenotypes has improved our knowledge of pituitary development and management of patients with hypopituitarism, both in terms of possible genetic counseling, and of early diagnosis of evolving anterior pituitary hormone deficiencies.

Genetics of Combined Pituitary Hormone Deficiency: Roadmap into the Genome Era

The genetic basis for combined pituitary hormone deficiency (CPHD) is complex, involving 30 genes in a variety of syndromic and nonsyndromic presentations. Molecular diagnosis of this disorder is valuable for predicting disease progression, avoiding unnecessary surgery, and family planning. We expect that the application of high throughput sequencing will uncover additional contributing genes and eventually become a valuable tool for molecular diagnosis. For example, in the last 3 years, six new genes have been implicated in CPHD using whole-exome sequencing. In this review, we present a historical perspective on gene discovery for CPHD and predict approaches that may facilitate future gene identification projects conducted by clinicians and basic scientists. Guidelines for systematic reporting of genetic variants and assigning causality are emerging. We apply these guidelines retrospectively to reports of the genetic basis of CPHD and summarize modes of inheritance and penetrance for each of the known genes. In recent years, there have been great improvements in databases of genetic information for diverse populations. Some issues remain that make molecular diagnosis challenging in some cases. These include the inherent genetic complexity of this disorder, technical challenges like uneven coverage, differing results from variant calling and interpretation pipelines, the number of tolerated genetic alterations, and imperfect methods for predicting pathogenicity. We discuss approaches for future research in the genetics of CPHD.

HESX1 mutations in patients with congenital hypopituitarism: variable phenotypes with the same genotype

INTRODUCTION

Mutations in the transcription factor HESX1 can cause isolated growth hormone deficiency (IGHD) or combined pituitary hormone deficiency (CPHD) with or without septo-optic dysplasia (SOD). So far there is no clear genotype-phenotype correlation.

PATIENTS AND RESULTS

We report four different recessive loss-of-function mutations in three unrelated families with CPHD and no midline defects or SOD. A homozygous p.R160C mutation was found by Sanger sequencing in two siblings from a consanguineous family. These patients presented with ACTH, TSH and GH deficiencies, severe anterior pituitary hypoplasia (APH) or pituitary aplasia (PA) and normal posterior pituitary. The p.R160C mutation was previously reported in a case with SOD, CPHD and ectopic posterior pituitary (EPP). Using exome sequencing, a homozygous p.I26T mutation was found in a Brazilian patient born to consanguineous parents. This patient had evolving CPHD, normal ACTH, APH and normal posterior pituitary (NPP). A previously reported patient homozygous for p.I26T had evolving CPHD and EPP. Finally, we identified compound heterozygous mutations in HESX1, p.[R159W];[R160H], in a patient with PA and CPHD. We showed that both of these mutations abrogate the ability of HESX1 to repress PROP1-mediated transcriptional activation. A patient homozygous for p.R160H was previously reported in a patient with CPHD, EPP, APH.

CONCLUSION

These three examples demonstrate that HESX1 mutations cause variable clinical features in patients, which suggests an influence of modifier genes or environmental factors on the phenotype.

Novel Mutations in HESX1 and PROP1 Genes in Combined Pituitary Hormone Deficiency

BACKGROUND/AIMS

The HESX1 gene is essential in forebrain development and pituitary organogenesis, and its mutations are the most commonly identified genetic cause of septo-optic dysplasia (SOD). The PROP1 gene is involved in anterior pituitary cell lineage specification and is commonly implicated in non-syndromic combined pituitary hormone deficiency (CPHD). We aimed to assess the involvement of HESX1 and PROP1 mutations in a cohort of patients with SOD and CPHD.

METHODS

Six patients with sporadic SOD and 16 patients with CPHD from 14 pedigrees were screened for mutations in HESX1 and PROP1 genes by exon sequencing. Half of the CPHD patients had variable associated clinical characteristics, such as hearing loss, orofacial cleft, kidney disorder or developmental delay. Novel variants were evaluated in silico and verified in SNP databases.

RESULTS

A novel heterozygous p.Glu102Gly mutation in the HESX1 gene and a novel homozygous p.Arg121Thr mutation in the PROP1 gene were detected in 2 pedigrees with CPHD. A small previously reported deletion in PROP1 c.301_302delAG was detected in a separate patient with CPHD, in heterozygous state. No mutations were identified in patients with SOD.

CONCLUSIONS

Our results expand the spectrum of mutations implicated in CPHD. The frequency of 15% of the PROP1 mutations in CPHD was low, likely due to the clinical heterogeneity of the cohort.

Combined pituitary hormone deficiency: current and future status

Over the last two decades, the understanding of the mechanisms involved in pituitary ontogenesis has largely increased. Since the first description of POU1F1 human mutations responsible for a well-defined phenotype without extra-pituitary malformation, several other genetic defects of transcription factors have been reported with variable degrees of phenotype-genotype correlations. However, to date, despite the identification of an increased number of genetic causes of isolated or multiple pituitary deficiencies, the etiology of most (80-90 %) congenital cases of hypopituitarism remains unsolved. Identifying new etiologies is of importance as a post-natal diagnosis to better diagnose and treat the patients (delayed pituitary deficiencies, differential diagnosis of a pituitary mass on MRI, etc.), and as a prenatal diagnosis to decrease the risk of early death (undiagnosed corticotroph deficiency for instance). The aim of this review is to summarize the main etiologies and phenotypes of combined pituitary hormone deficiencies, associated or not with extra-pituitary anomalies, and to suggest how the identification of such etiologies could be improved in the near future.

Identification of HESX1 mutations in Kallmann syndrome

OBJECTIVE

To determine whether HESX1 mutations are present in patients with idiopathic hypogonadotropic hypogonadism (IHH)/Kallmann syndrome (KS).

DESIGN

Polymerase chain reaction-based DNA sequencing was performed on 217 well-characterized IHH/KS patients. Putative missense mutations were analyzed by sorting intolerant from tolerant (SIFT) and Clustal Ω.

SETTING

Academic medical center.

PATIENT(S)

Two hundred seventeen patients with IHH/KS and 192 controls.

INTERVENTION(S)

Deoxyribonucleic acid was extracted from patients and controls; genotype/phenotype comparisons were made.

MAIN OUTCOME MEASURE(S)

Deoxyribonucleic acid sequence of HESX1, SIFT analysis, and ortholog alignment.

RESULT(S)

Two novel heterozygous missense mutations (p.H42Y and p.V75L) and previously reported heterozygous missense mutation p.Q6H in HESX1 were identified in 3 of 217 patients (1.4%). All were males with KS. Both p.Q6H and p.H42Y were predicted to be deleterious by SIFT, whereas p.V75L was conserved in 8 of 9 species. No other IHH/KS gene mutations were present.

CONCLUSION(S)

HESX1 mutations may cause KS in addition to more severe phenotypes. Our findings expand the phenotypic spectrum of HESX1 mutations in humans, thereby broadening its role in development.

Unilateral agenesis of internal carotid artery associated with congenital combined pituitary hormone deficiency and pituitary stalk interruption without HESX1, LHX4 or OTX2 mutation: a case report

Agenesis of internal carotid artery (ICA) is an unusual finding in subjects with congenital Combined Pituitary hormone deficiency (CPHD) with only nine cases being reported to date but to our best knowledge none of them was genetically investigated. A 10-years old girl presented with severe growth failure (height 103 cm) with substantial bone age delay (3 years). She had no history of perinatal insults or familial CPHD. There was no evidence of mental retardation or craniofacial dysmorphism or ophtalmological abnormalities. She was first diagnosed with GH and TSH deficiency. Cerebral magnetic resonance imaging (MRI) showed hypoplastic anterior pituitary, flat sella turcica, absent pituitary stalk with ectopic posterior pituitary as well as agenesis of the left ICA and the left carotid canal. Genomic analysis of pituitary transcription factor HESX1, LHX4 and OTX2 showed no mutations. Treatment with GH and thyroxine was started. The patient remained free of neurovascular symptoms for 5 years but she presented at the age of 15 years with delayed puberty related to an evolving gonadotropin deficiency. ICA agenesis associated with CPHD is unusual and is often asymptomatic in children. Since the CPHD with pituitary stalk interruption cannot be due to HESX1, LHX4 or OTX2 mutation in our case, other pathogenetic mechanisms may be responsible for CPHD associated with unilateral ICA agenesis.

Three unrelated patients with congenital anterior pituitary aplasia and a characteristic physical and neuropsychological phenotype: a new syndrome?

Anterior pituitary aplasia (APA) is a very rare cause of congenital-onset multiple pituitary hormone deficiency (CO-MPHD). We report on molecular analysis and clinical follow-up of three previously reported cases of APA [Scommegna et al., 2004], who share a characteristic physical and neuropsychological profile. Mutation analysis of genes encoding transcription factors involved in pituitary development (PROP1, POUF1, HESX1, LHX3, and LHX4) did not demonstrate a any mutation. In order to identify the genetic cause underlying the phenotypes we performed an array-based comparative genomic hybridization (array-CGH), which showed a cryptic interstitial deletion of 9p (200 kb), including the TEK and MOBKL2B, in one patient. Although an apparently identical deletion was carried by the clinically normal father, we assumed that the patient's phenotype might be due to a recessive mutation in the other allele. However, sequence analysis of exons and splice junctions of these genes did not detect pathogenic or predisposing variants in the three patients. We suggest that the constellation of clinical signs in these patients constitutes a previously undescribed syndrome, whose genetic cause has yet to be identified.

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.

Panhypopituitarism presenting as life-threatening heart failure caused by an inherited microdeletion in 1q25 including LHX4

Clinical presentation of hypopituitarism in the neonate may be variable, ranging from absent to severe nonspecific symptoms and may be life-threatening in patients with adrenocorticotropic hormone deficiency. The LIM homeobox gene 4 (LHX4) transcription factor regulates early embryonic development of the anterior pituitary gland. Autosomal dominant mutations in LHX4 cause congenital hypopituitarism with variable combined pituitary hormone deficiency (CPHD). We report on a neonate with unexplained heart failure and minor physical anomalies, suggesting a midline defect. She was diagnosed with complete CPHD. Cardiac function was rescued by replacement with hydrocortisone and thyroxine; hypoglycaemia stopped under growth hormone therapy. Magnetic resonance imaging revealed a dysgenetic pituitary gland suggesting an early developmental defect. Array comparative genomic hybridization showed a maternally inherited 1.5-megabase microdeletion in 1q25.2q25.3, including the LHX4 gene. Haploinsufficiency of LHX4 likely explains the predominant pituitary phenotype in the proposita and we suggest variable intrafamilial penetrance of the inherited microdeletion. To the best of our knowledge, we are the first to report on heart failure as a rare nonspecific symptom of treatable CPHD in the newborn. Variably penetrant pituitary insufficiency, including this severe and atypical presentation, can be correlated with LHX4 insufficiency and highlights the role of LHX4 for pituitary development.

Aged PROP1 deficient dwarf mice maintain ACTH production

Humans with PROP1 mutations have multiple pituitary hormone deficiencies (MPHD) that typically advance from growth insufficiency diagnosed in infancy to include more severe growth hormone (GH) deficiency and progressive reduction in other anterior pituitary hormones, eventually including adrenocorticotropic hormone (ACTH) deficiency and hypocortisolism. Congenital deficiencies of GH, prolactin, and thyroid stimulating hormone have been reported in the Prop1^null (Prop1^-/-) and the Ames dwarf (Prop1^df/df) mouse models, but corticotroph and pituitary adrenal axis function have not been thoroughly investigated. Here we report that the C57BL6 background sensitizes mutants to a wasting phenotype that causes approximately one third to die precipitously between weaning and adulthood, while remaining homozygotes live with no signs of illness. The wasting phenotype is associated with severe hypoglycemia. Circulating ACTH and corticosterone levels are elevated in juvenile and aged Prop1 mutants, indicating activation of the pituitary-adrenal axis. Despite this, young adult Prop1 deficient mice are capable of responding to restraint stress with further elevation of ACTH and corticosterone. Low blood glucose, an expected side effect of GH deficiency, is likely responsible for the elevated corticosterone level. These studies suggest that the mouse model differs from the human patients who display progressive hormone loss and hypocortisolism.

The role of homeodomain transcription factors in heritable pituitary disease

The anterior pituitary gland secretes hormones that regulate developmental and physiological processes, including growth, the stress response, metabolic status, reproduction and lactation. During embryogenesis, cellular determination and differentiation events establish specialized hormone-secreting cell types within the anterior pituitary gland. These developmental decisions are mediated in part by the actions of a cascade of transcription factors, many of which belong to the homeodomain class of DNA-binding proteins. The discovery of some of these regulatory proteins has facilitated genetic analyses of patients with hormone deficiencies. The findings of these studies reveal that congenital defects-ranging from isolated hormone deficiencies to combined pituitary hormone deficiency syndromes-are sometimes associated with mutations in the genes encoding pituitary-acting developmental transcription factors. The phenotypes of affected individuals and animal models have together provided useful insights into the biology of these transcription factors and have suggested new hypotheses for testing in the basic science laboratory. Here, we summarize the gene regulatory pathways that control anterior pituitary development, with emphasis on the role of the homeodomain transcription factors in normal pituitary organogenesis and heritable pituitary disease.

Three Japanese patients with congenital pituitary hormone deficiency and ophthalmological anomalies

The clinical phenotype of congenital pituitary hormone deficiency is variable and can be associated with a number of structural abnormalities of the central nervous system. We report three Japanese patients with congenital pituitary hormone deficiency and ophthalmological anomalies. Two of the patients initially showed strabismus and unilateral optic nerve hypoplasia. Thereafter, growth failure became evident, leading to the diagnosis of pituitary hormone deficiency. The other patient had severe congenital hypopituitarism with respiratory distress and hypoglycemia from the first day of life. In addition, he had prolonged jaundice and impaired liver function with bilateral optic nerve hypoplasia. Neuroimaging of the pituitary region in all three patients demonstrated a small anterior pituitary lobe and no pituitary stalk. Our findings indicate that clinical variability of congenital hypopituitarism must be considered. In a patient with ophthalmological symptoms, endocrine evaluation and neuroimaging of the CNS including the pituitary region should be considered.

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

OBJECTIVE

Mutations in HESX1 represent a rare cause of GH deficiency (GHD) associated with a broad spectrum of other anomalies. We searched for causative mutations in a cohort of 244 Italian patients affected by combined and isolated GHD (IGHD).

METHODS

The HESX1 gene-coding region and exon-intron boundaries were screened by denaturing HPLC scanning.

RESULTS

A novel mutation adjacent to the invariant donor splice site of intron 2 (c.357+3G>A) was identified at the heterozygous state in an IGHD patient. The in vitro and in vivo mRNA analysis of the wild-type HESX1 allele revealed the presence of the whole cDNA and two isoforms lacking exon 2 and exons 2-3 respectively. The mutant HESX1 allele yielded only two splicing products, the whole cDNA and the cDNA missing exons 2-3, whereas the mRNA lacking exon 2 was absent. An in vitro assay demonstrated that the exon 2-deleted mRNA, predicting a prematurely truncated protein, is subjected to nonsense-mediated mRNA decay (NMD).

CONCLUSIONS

The c.357+3G>A mutation prevents the generation of one of the alternative isoforms normally produced by the wild-type allele, predicting a truncated HESX1 protein. The mutation is likely to cause IGHD in the heterozygous patient by interfering with the downregulation of HESX1 expression mediated by alternative splicing and NMD. Our results open new insight into the mechanism of HESX1 regulation suggesting that the coupling of alternative splicing and NMD might play a fundamental role in directing the HESX1 expression, and that the alteration of this process might lead to severe consequences.

Septo-optic dysplasia and other midline defects: the role of transcription factors: HESX1 and beyond

Septo-optic dysplasia (SOD) is a highly heterogeneous condition comprising variable phenotypes including midline and forebrain abnormalities, optic nerve and pituitary hypoplasia. Most instances of SOD are sporadic and several aetiologies including drug and alcohol abuse have been suggested to account for the pathogenesis of the condition. However, a number of familial cases have been described with an increasing number of mutations in developmental transcription factors including HESX1, SOX2, SOX3 and OTX2 being implicated in its aetiology. These factors are essential for normal forebrain/pituitary development, and disruptions to these genes could account for the features observed in SOD and other midline disorders. The variable phenotypes observed within the condition are most likely due to the varying contributions of genetic and environmental factors. This review will discuss the current knowledge about SOD. Further study of these and other novel factors may shed light on the complex aetiology of this condition.

A novel homozygous HESX1 mutation causes panhypopituitarism without midline defects and optic nerve anomalies

OBJECTIVE

There are many genes reported to have been associated with combined pituitary hormone deficiencies, but mutations in HESX1 strongly correlate with septo-optic dysplasia. Our aim was to determine the cause of panhypopituitarism in our patient.

PATIENTS AND METHODS

We studied an 8-month-old child having panhypopituitarism. The coding exons of PIT1, PROP1, LHX3, and HESX1 genes were amplified. Direct sequencing was done after denaturing HLPC.

RESULTS

We identified a novel homozygous mutation (R160H) within the homeodomain of HESX1, which, to our knowledge, is the first to be described in humans. Neuroimaging studies revealed anterior pituitary aplasia, a normal posterior pituitary gland, and a thin pituitary stalk but no midline abnormalities. Optic nerve studies showed no pathology. This mutation is also carried in the parents of the affected child in a heterozygous pattern, suggesting an autosomal recessive inheritance.

CONCLUSION

These data demonstrate that homozygous HESX1 mutation causing an R160H substitution can result in panhypopituitarism without midline defects.

Septo-optic dysplasia

This review summarises the key clinical features of septo-optic dysplasia (SOD), the significant inroads that progress in genetics has made into our understanding of the aetiology of the condition over the last decade, and the pitfalls and challenges that we face in the management of these phenotypically variable patients.

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.

The molecular basis of hypopituitarism

Hypopituitarism is defined as the deficiency of one or more of the hormones secreted by the pituitary gland. Several developmental factors necessary for pituitary embryogenesis and hormone secretion have been described, and mutations of these genes in humans provide a molecular understanding of hypopituitarism. Genetic studies of affected patients and their families provide insights into possible mechanisms of abnormal pituitary development; however, mutations are rare. This review characterizes several of these developmental proteins and their role in the pathogenesis of hypopituitarism. Continuing research is required to better understand the complexities and interplay between these pituitary factors and to make improvements in genetic diagnosis that can lead to early detection and provide a future cure.

A novel SNP of the Hesx1 gene in bovine and its associations with average daily gain

As an essential repressor, the homeobox gene Hesx1/HESX1 is required within the anterior neural plate for normal forebrain development. Mutations within the Hesx1 gene have been associated with GH deficiency or combined pituitary hormone deficiency. We detected the polymorphism of Hesx1 gene by PCR-SSCP and DNA sequencing methods in 702 individuals from four Chinese cattle breeds. A novel single nucleotide polymorphism (SNP) (IVS1 + 382T > C) was detected. The frequencies of genotype TC in four breeds were 0.000-0.222. Polymorphism of the Hesx1 gene was shown to be associated with growth in the Nanyang breed. Individuals with genotype TC was significantly lower average daily gain than TT at 18 months (P < 0.05).

Effects of genetic variability of the caprine homeobox transcription factor HESX1 gene on performance traits

HESX1 plays a key role in the development of the forebrain and pituitary gland and produces potential effects on performance traits. The objective of this study was to detect and assess the associations of the possible polymorphisms of six loci within HESX1 gene with performance traits in Chinese 1,119 goats. Only one novel SNP (NM_001494116:g.307049A > G) locating on IVS1 + 348A > G was identified and detected by HaeIII forced-RFLP-PCR. The frequencies of allele "G" varied from 0.025 to 0.245 in analyzed populations with the Hardy-Weinberg equilibrium (P > 0.05). Genotypic and allelic frequencies were found to be significantly different in four breeds (chi(2) = 147.674, df = 6, P < 0.001; chi(2) = 157.250, df = 3, P < 0.001, respectively), implying that the distribution of genotypic and allelic frequencies of goat HESX1 gene was significantly associated with different goat utilities (cashmere, meat and dairy). Association analysis results revealed no significant effects of caprine HESX1 gene on body sizes in XNSN population (P > 0.05) and cashmere traits in IMWC population (P > 0.05). Significant statistical of HESX1 gene with body weight was found (*P < 0.05). The genotype AA showed significantly higher body weight than those of AG in 2-year-old age (*P < 0.05), while the AA genotype was senior to AG genotype in 4-year-old body weight trait (*P < 0.05). These suggestions indicated that the HESX1 gene has significant effect on goat body weight depending on ages, which is accordance with the function repressor of the HESX1.

[Congenital hypogonadotropic hypogonadism]

Congenital hypogonadotropic hypogonadism is defined by reduced steroid hormone synthesis and secretion due to low LH and FSH secretion. It is a rare disease with an unknown prevalence (about 1/5000). It results from a fetal defect in GnRH neuron migration, a defect of pituitary development or from a functional defect of the hypothalamopituitary axis between GnRH neurons and gonadotropic cells. The diagnosis should be considered at birth in males with micropenis, during adolescence in case of delayed puberty or absent puberty, and during adulthood in case of infertility. It may be restricted to the gonadotropic axis, combined with other endocrine system defects or be part of a complex syndrome. Several gene defects have now been described. Molecular studies should be performed to confirm the diagnosis and to help provide appropriate genetic counseling. Treatment to induce puberty should be provided at adolescence, followed by hormonal substitution treatment during adulthood. Specific infertility treatment may also be proposed but patients with the dominant form of gonadotropic deficiency should be informed of the risk of transmission.

Analysis of mouse models carrying the I26T and R160C substitutions in the transcriptional repressor HESX1 as models for septo-optic dysplasia and hypopituitarism

A homozygous substitution of the highly conserved isoleucine at position 26 by threonine (I26T) in the transcriptional repressor HESX1 has been associated with anterior pituitary hypoplasia in a human patient, with no forebrain or eye defects. Two individuals carrying a homozygous substitution of the conserved arginine at position 160 by cysteine (R160C) manifest septo-optic dysplasia (SOD), a condition characterised by pituitary abnormalities associated with midline telencephalic structure defects and optic nerve hypoplasia. We have generated two knock-in mouse models containing either the I26T or R160C substitution in the genomic locus. Hesx1(I26T/I26T) embryos show pituitary defects comparable with Hesx1(-/-) mouse mutants, with frequent occurrence of ocular abnormalities, although the telencephalon develops normally. Hesx1(R160C/R160C) mutants display forebrain and pituitary defects that are identical to those observed in Hesx1(-/-) null mice. We also show that the expression pattern of HESX1 during early human development is very similar to that described in the mouse, suggesting that the function of HESX1 is conserved between the two species. Together, these results suggest that the I26T mutation yields a hypomorphic allele, whereas R160C produces a null allele and, consequently, a more severe phenotype in both mice and humans.

A novel dominant negative mutation of OTX2 associated with combined pituitary hormone deficiency

CONTEXT

Combined pituitary hormone deficiency (CPHD) is characterized by deficiencies in more than one anterior pituitary hormone. Mutations in developmental factors responsible for pituitary cell specification and gene expression have been found in CPHD patients. OTX2, a bicoid class homeodomain protein, is necessary for both forebrain development and transactivation of the HESX1 promoter, but as of yet, has not been associated with CPHD.

OBJECTIVE

The goal of this study was to identify and characterize novel mutations in pituitary specific transcription factors from CPHD patients.

DESIGN

Genomic DNA was isolated from patients with hypopituitarism to amplify and sequence eight pituitary specific transcription factors (HESX1, LHX3, LHX4, OTX2, PITX2, POU1F1, PROP1, and SIX6). Characterization of novel mutations is based on structural and functional studies.

RESULTS

We describe two unrelated children with CPHD who presented with neonatal hypoglycemia, and deficiencies of GH, TSH, LH, FSH, and ACTH. Magnetic resonance imaging revealed anterior pituitary hypoplasia with an ectopic posterior pituitary. A novel heterozygous OTX2 mutation (N233S) was identified. Wild-type and mutant OTX2 proteins bind equivalently to bicoid binding sites, whereas mutant OTX2 revealed decreased transactivation.

CONCLUSIONS

A novel mutation in OTX2 binds normally to target genes and acts as a dominant negative inhibitor of HESX1 gene expression. This suggests that the expression of HESX1, required for spaciotemporal development of anterior pituitary cell types, when disrupted, results in an absent or underdeveloped anterior pituitary with diminished hormonal expression. These results demonstrate a novel mechanism for CPHD and extend our knowledge of the spectrum of gene mutations causing CPHD.

Molecular analysis of PROP1, PIT1, HESX1, LHX3, and LHX4 shows high frequency of PROP1 mutations in patients with familial forms of combined pituitary hormone deficiency

Combined Pituitary Hormone Deficiency (CPHD) is a prevalent disease in Neuroendocrinology services. The genetic form of CPHD may originate from mutations in pituitary transcription factor (PTF) genes and the pituitary image in these cases may give a clue of what PTF is most probably mutated: defects in LHX4 are usually associated with ectopic posterior pituitary (EPP); defects in LHX3, PIT1, and PROP1, with normally placed posterior pituitary (NPPP); HESX1 mutations are associated with both.

OBJECTIVE

To identify mutations in PTF genes in patients with idiopathic hypopituitarism followed in our service, based on the presence or absence of EPP on sellar MRI.

METHODS

Forty patients with idiopathic hypopituitarism (36 families, 9 consanguineous), followed in the Neuroendocrinology Outpatient Clinic of UNIFESP, Brazil, were submitted to sequencing analyses of PTF genes as follows: LHX3, HESX1, PIT1, and PROP1 were sequenced in patients with NPPP (26/40) and HESX1 and LHX4 in patients with EPP (14/40).

RESULTS

We identified only PROP1 mutations in 9 out of 26 patients with CPHD and NPPP (35%). Since eight of them came from 4 consanguineous families, the prevalence of PROP1 mutations was higher when only consanguineous families were considered (44%, 4/9). At the end of the study, we decided to sequence PROP1 in patients with EPP, just to confirm that they were not candidates for PROP1 mutations. No patients with EPP had PROP1 or other PTF mutations.

CONCLUSIONS

Patients with idiopathic CPHD and NPPP, born from consanguineous parents, are the strong candidates for PROP1 mutations. Other developmental gene(s) may be involved in the genesis of idiopathic hypopituitarism associated with EPP.

Unusual phenotypic features in a patient with a novel splice mutation in the GHRHR gene

Isolated growth hormone deficiency (IGHD) may be of genetic origin. One of the few genes involved in that condition encodes the growth hormone releasing hormone receptor (GHRHR) that, through its ligand (GHRH), plays a pivotal role in the GH synthesis and secretion by the pituitary. Our objective is to describe the phenotype of two siblings born to a consanguineous union presenting with short stature (IGHD) and Magnetic Resonance Imaging (MRI) abnormalities, and to identify the molecular basis of this condition. Our main outcome measures were clinical and endocrinological investigations, MRI of the pituitary region, study of the GHRHR gene sequence and transcripts. In both patients, the severe growth retardation (-5SD) was combined with anterior pituitary hypoplasia. In addition to these classical phenotypic features for IGHD, one of the patients had a Chiari I malformation, an arachnoid cyst, and a dysmorphic anterior pituitary. A homozygous sequence variation in the consensus donor splice site of intron 1 (IVS1 + 2T > G) of the GHRHR gene was identified in both patients. Using in vitro transcription assay, we showed that this mutation results in abnormal splicing of GHRHR transcripts. In this report, which broadens the phenotype associated with GHRHR defects, we discuss the possible role of the GHRHR in the proper development of extrapituitary structures, through a mechanism that could be direct or secondary to severe GH deficiency.

Heterozygous mutation of HESX1 causing hypopituitarism and multiple anatomical malformations without features of septo-optic dysplasia

Isolated GH deficiency or combined pituitary hormone deficiencies have been associated with mutations in transcription factors encoding genes that control organogenesis or cell differentiation. Among these factors, Hesx1 is essential for the development of the optic nerve and regulates some of the earliest stages in pituitary development and is intimately involved in orchestrating the expression of other factors involved in pituitary organogenesis. Mutations in HESX1 are reported in patients with hypopituitarism either with typical septo-optic dysplasia (SOD) or with neuromorphological abnormalities not included in classical SOD. The present report describes clinical features, biochemical parameters, and characterization of a missense mutation (Gln6His) in exon1 of HESX1 in a pre-pubertal child who progressively developed multiple hypopituitarism, firstly GH and, afterwards, TSH and ACTH deficiencies, in a pluri-malformative syndrome characterized by short stature and anatomical malformations not associated with a classical SOD phenotype. This finding further supports the necessity to stay alert in evaluating a gene that plays a minor role in the pathogenesis of sporadic hypopituitarism, such as HESX1 gene even when the phenotype does not fit in with a classical SOD syndrome.

[Clinical and genetic aspects of combined pituitary hormone deficiencies]

DEFINITION

Congenital hypopituitarism is characterized by multiple pituitary hormone deficiency, including somatotroph, thyrotroph, lactotroph, corticotroph or gonadotroph deficiencies, due to mutations of pituitary transcription factors involved in pituitary ontogenesis.

INCIDENCE

Congenital hypopituitarism is rare compared with the high incidence of hypopituitarism induced by pituitary adenomas, transsphenoidal surgery or radiotherapy. The incidence of congenital hypopituitarism is estimated to be between 1:3000 and 1:4000 births.

CLINICAL SIGNS

Clinical presentation is variable, depending on the type and severity of deficiencies and on the age at diagnosis. If untreated, main symptoms include short stature, cognitive alterations or delayed puberty.

DIAGNOSIS

A diagnosis of combined pituitary hormone deficiency (CPHD) must be suspected when evident causes of hypopituitarism (sellar tumor, postsurgical or radioinduced hypopituitarism...) have been ruled out. Clinical, biological and radiological work-up is very important to better determine which transcription factor should be screened. Confirmation is provided by direct sequencing of the transcription factor genes.

AETIOLOGY

Congenital hypopituitarism is due to mutations of several genes encoding pituitary transcription factors. Phenotype varies with the factor involved: PROP1 (somatolactotroph, thyrotroph, gonadotroph and sometimes corticotroph deficiencies; pituitary hyper and hypoplasia), POU1F1 (somatolactotroph and thyrotroph deficiencies, pituitary hypoplasia), HESX1 (variable pituitary deficiencies, septo-optic dysplasia), and less frequently LHX3 (somatolactotroph, thyrotroph and gonadotroph deficiencies, limited head and neck rotation) and LHX4 (variable pituitary deficiencies, ectopic neurohypophysis, cerebral abnormalities).

MANAGEMENT

An appropriate replacement of hormone deficiencies is required. Strict follow-up is necessary because patients develop new deficiencies (for example late onset corticotroph deficiency in patients with PROP1 mutations). GENETIC COUNSELLING: Type of transmission varies with the factor and the mutation involved (recessive transmission for PROP1 and LHX3, dominant for LHX4, autosomal or recessive for POU1F1 and HESX1).

PROGNOSIS

It is equivalent to patients without pituitary deficiencies if treatment is started immediately when diagnosis is confirmed, and if a specialized follow-up is performed.

Septo-optic dysplasia - novel insights into the aetiology

Septo-optic dysplasia (SOD) is a highly heterogeneous condition comprising a variable phenotype of optic nerve hypoplasia, midline brain abnormalities and pituitary hypoplasia with consequent endocrine deficits. The majority of cases are sporadic and several aetiologies have been suggested to account for the pathogenesis of the condition. However, a number of familial cases have been described and the identification of mutations in key developmental genes including HESX1, SOX2 and SOX3 in patients with SOD and associated phenotypes suggests that a genetic causation is likely in the more common sporadic cases of the condition. The precise aetiology of SOD is most likely multifactorial involving contributions from environmental factors in addition to an important role for crucial developmental genes. The variability of the penetrance and phenotypes within a single SOD pedigree may also suggest a complex interaction between genetics and the environment, and at present, the understanding of these interactions is rudimentary. Further study of these critical factors may shed light on the aetiology of this complex disorder. We have reviewed recent literature selecting relevant references based on the keywords HESX1, SOX2, SOX3, Septo-optic dysplasia, genetics and pituitary development.

Developmental disorders of the hypothalamus and pituitary gland associated with congenital hypopituitarism

The pituitary gland is a complex organ secreting six hormones from five different cell types. It is the end product of a carefully orchestrated pattern of expression of signalling molecules and transcription factors. Naturally occurring and transgenic murine models have demonstrated a role for many of these molecules in the aetiology of congenital hypopituitarism. These include the transcription factors HESX1, PROP1, POU1F1, LHX3, LHX4, PITX1, PITX2, SOX2 and SOX3. The expression pattern of these transcription factors dictates the phenotype that results when the gene encoding the relevant transcription factor is mutated. The highly variable phenotype may consist of isolated hypopituitarism or more complex disorders such as septo-optic dysplasia and holoprosencephaly. However, the overall incidence of mutations in known transcription factors in patients with hypopituitarism is low, indicating that many genes remain to be identified; characterization of these will further elucidate the pathogenesis of this complex condition and also shed light on normal pituitary development and function.

Hypopituitarism oddities: congenital causes

BACKGROUND

The last 15 years have witnessed an explosion in our knowledge of hypothalamo-pituitary development, acquired mainly from naturally-occurring and transgenic animal models. A complex genetic cascade dictates organ commitment, cell differentiation and cell proliferation within the anterior pituitary. Mutations in genes encoding both signalling molecules and transcription factors have been implicated in the aetiology of hypopituitarism, with or without other syndromic features, in mice and humans. These include HESX1, LHX3, LHX4, PROP1, POU1F1 and, more recently, SOX3 and SOX2. Phenotypes associated with mutations in genes encoding these factors and their inheritance may be highly variable.

PHENOTYPIC PROFILE

Mutations in genes implicated in early pituitary development may be associated with extrapituitary phenotypes, which in turn may be highly variable. For example, dominant and recessive mutations in HESX1 may be associated with septo-optic dysplasia, combined pituitary hormone deficiency (CPHD) and isolated growth hormone (GH) deficiency. Duplications and polyalanine expansions within the transcription factor SOX3 have recently been described in association with infundibular hypoplasia, hypopituitarism and variable mental retardation, whilst mutations in SOX2 are associated with variable hypopituitarism in association with learning difficulties, oesophageal atresia and anophthalmia. Mutations within the LIM domain gene LHX3 are associated with a recessive phenotype characterised by deficiencies in GH, thyroid-stimulating hormone (TSH), luteinising hormone (LH) and follicle-stimulating hormone (FSH) with sparing of the corticotrophs, in association with a short stiff neck with limited rotation. A single mutation has been described within the LHX4 gene, and is dominantly inherited and associated with GH, TSH and adrenocorticotrophic hormone (ACTH) deficiency. The mutation is associated with a hypoplastic anterior pituitary, an undescended posterior pituitary and pointed cerebellar tonsils. PROP1 and POU1F: Recessive mutations within the pituitary-specific transcription factor Prophet of Pit1, or PROP1, are associated with CPHD (GH, prolactin [PRL] and TSH deficiency with additional LH and FSH deficiency). An enlarged sella turcica with appearances suggestive of a pituitary tumour is occasionally observed in association with PROP1 mutations. ACTH deficiency can evolve in a number of patients, reflecting the need for constant review of the phenotype. Mutations within POU1F1 are associated with GH, TSH and PRL deficiencies, with the TSH deficiency being highly variable. Magnetic resonance imaging reveals either a normal or hypoplastic anterior pituitary. Mutations may be either dominantly or recessively inherited, and the R271W mutation, which is believed to act as a dominant negative mutation, represents a mutational 'hot spot'.

CONCLUSIONS

In the future, genetic analysis together with functional analysis of the mutations at the protein level will have a greater role to play in understanding the mechanisms leading to particular hypopituitary phenotypes and in predicting the evolution of these disorders. However, there is no substitute for careful delineation of the clinical, biochemical and neuroradiological phenotype prior to undertaking genetic studies.

DNMT1 interacts with the developmental transcriptional repressor HESX1

Hesx1 is a highly conserved homeobox gene present in vertebrates, but absent from invertebrates. Gene targeting experiments in mice have shown that this transcriptional repressor is required for normal forebrain and pituitary development. In humans, mutations in HESX1 impairing either its repressing activity or DNA binding properties lead to a comparable phenotype to that observed in Hesx1 deficient mice. In an attempt to gain insights into the molecular function of HESX1, we have performed a yeast two-hybrid screen and identified DNA methyltransferase 1 (DNMT1) as a HESX1 binding protein. We show that Dnmt1 is co-expressed with Hesx1 within the anterior forebrain and in the developing Rathke's pouch. Mapping of the interacting regions indicates that the entire HESX1 protein is required to establish binding to a portion of the N-terminus of DNMT1 and its catalytic domain in the C-terminus. The HESX1–DNMT1 complexes can be immunoprecipitated in cells and co-localise in the nucleus. These results establish a link between HESX1 and DNMT1 and suggest a novel mechanism for the repressing properties of HESX1.

A novel missense mutation (P366T) of the LHX4 gene causes severe combined pituitary hormone deficiency with pituitary hypoplasia, ectopic posterior lobe and a poorly developed sella turcica

LIM homeodomain transcription factors regulate many aspects of development in multicellular organisms. LHX4/Lhx4 is a protein that is essential for pituitary development and motor neuron specification in mammals. In human, a heterozygous splicing mutation of the LHX4 gene was reported in a family with combined pituitary hormone deficiencies (CPHD). In addition to CPHD, these patients were characterized by small sella turcica and chiari malformation. Here we report a Japanese patient with CPHD (GH, PRL, TSH, LH, FSH, and ACTH deficiency) due to a novel missense mutation (P366T) of the LHX 4 gene. She showed severe respiratory disease and hypoglycemia soon after birth. Brain MRI demonstrated hypoplastic anterior pituitary, ectopic posterior lobe, a poorly developed sella turcica, and chiari malformation. Sequence analysis of the LHX 4 gene identified a heterozygous missense mutation (P366T) in exon 6, which was present in LIM4 specific domain. Neither of the patient's parents harbored this mutation, indicating de novo mutation.

Hypothalamic and pituitary development: novel insights into the aetiology

The anterior pituitary gland is a central regulator of growth, reproduction and homeostasis, and is the end-product of a carefully orchestrated pattern of expression of signalling molecules and transcription factors leading to the development of this complex organ secreting six hormones from five different cell types. Naturally occurring and transgenic murine models have demonstrated a role for many of these molecules in the aetiology of combined pituitary hormone deficiency (CPHD). These include the transcription factors HESX1, PROP1, POU1F1, LHX3, LHX4, TBX19, SOX2 and SOX3. The expression pattern of these transcription factors dictates the phenotype that results when the gene encoding the relevant transcription factor is mutated. The highly variable phenotype may consist of isolated hypopituitarism, or more complex disorders such as septo-optic dysplasia and holoprosencephaly. Since mutations in any one transcription factor are uncommon, and since the overall incidence of mutations in known transcription factors is low in patients with CPHD, it is clear that many genes remain to be identified, and the characterization of these will further elucidate the pathogenesis of these complex conditions and also shed light on normal pituitary development.

Lack of the murine homeobox gene Hesx1 leads to a posterior transformation of the anterior forebrain

The homeobox gene Hesx1 is an essential repressor that is required within the anterior neural plate for normal forebrain development in mouse and humans. Combining genetic cell labelling and marker analyses, we demonstrate that the absence of Hesx1 leads to a posterior transformation of the anterior forebrain (AFB) during mouse development. Our data suggest that the mechanism underlying this transformation is the ectopic activation of Wnt/beta-catenin signalling within the Hesx1 expression domain in the AFB. When ectopically expressed in the developing mouse embryo, Hesx1 alone cannot alter the normal fate of posterior neural tissue. However, conditional expression of Hesx1 within the AFB can rescue the forebrain defects observed in the Hesx1 mutants. The results presented here provide new insights into the function of Hesx1 in forebrain formation.

HESX1 mutations are an uncommon cause of septooptic dysplasia and hypopituitarism

CONTEXT

Mutations in the transcription factor HESX1 have previously been described in association with septooptic dysplasia (SOD) as well as isolated defects of the hypothalamic-pituitary axis.

OBJECTIVE

Given that previous screening was carried out by SSCP detection alone and limited to coding regions, we performed an in-depth genetic analysis of HESX1 to establish the true contribution of HESX1 genetic defects to the etiology of hypopituitarism.

DESIGN

Nonfamilial patients (724) with either SOD (n = 314) or isolated pituitary dysfunction, optic nerve hypoplasia, or midline neurological abnormalities (n = 410) originally screened by SSCP were rescreened by heteroduplex detection for mutations in the coding and regulatory regions of HESX1. In addition, direct sequencing of HESX1 was performed in 126 patients with familial hypopituitarism from 66 unrelated families and in 11 patients born to consanguineous parents.

PATIENTS

All patients studied had at least one of the three classical features associated with SOD (optic nerve hypoplasia, hypopituitarism, midline forebrain defects).

RESULTS

Novel sequence changes identified included a functionally significant heterozygous mutation at a highly conserved residue (E149K) in a patient with isolated GH deficiency and digital abnormalities. The overall incidence of coding region mutations within the cohort was less than 1%.

CONCLUSIONS

Mutations within HESX1 are a rare cause of SOD and hypopituitarism. However, the large number of familial patients with SOD in whom no mutations were identified is suggestive of an etiological role for other genetic factors. Furthermore, we have found that within our cohort SOD is associated with a reduced maternal age compared with isolated defects of the hypothalamopituitary axis.