Novel FGF8 mutations associated with recessive holoprosencephaly, craniofacial defects, and hypothalamo-pituitary dysfunction

Appetite- and Weight-Regulating Neuroendocrine Circuitry in Hypothalamic Obesity

Since hypothalamic obesity (HyOb) was first described over 120 years ago by Joseph Babinski and Alfred Fröhlich, advances in molecular genetic laboratory techniques have allowed us to elucidate various components of the intricate neurocircuitry governing appetite and weight regulation connecting the hypothalamus, pituitary gland, brainstem, adipose tissue, pancreas, and gastrointestinal tract. On a background of an increasing prevalence of population-level common obesity, the number of survivors of congenital (eg, septo-optic dysplasia, Prader-Willi syndrome) and acquired (eg, central nervous system tumors) hypothalamic disorders is increasing, thanks to earlier diagnosis and management as well as better oncological therapies. Although to date the discovery of several appetite-regulating peptides has led to the development of a range of targeted molecular therapies for monogenic obesity syndromes, outside of these disorders these discoveries have not translated into the development of efficacious treatments for other forms of HyOb. This review aims to summarize our current understanding of the neuroendocrine physiology of appetite and weight regulation, and explore our current understanding of the pathophysiology of HyOb.

Whole-genome sequencing analysis in fetal structural anomalies: novel phenotype-genotype discoveries

OBJECTIVES

The identification of structural variants and single-nucleotide variants is essential in finding molecular etiologies of monogenic genetic disorders. Whole-genome sequencing (WGS) is becoming more widespread in genetic disease diagnosis. However, data on its clinical utility remain limited in prenatal practice. We aimed to expand our understanding of implementing WGS in the genetic diagnosis of fetal structural anomalies.

METHODS

We employed trio WGS with a minimum coverage of 40× on the MGI DNBSEQ-T7 platform in a cohort of 17 fetuses presenting with aberrations detected by ultrasound, but uninformative findings of standard chromosomal microarray analysis (CMA) and exome sequencing (ES).

RESULTS

Causative genetic variants were identified in two families, with an increased diagnostic yield of 11.8% (2/17). Both were exon-level copy-number variants of small size (3.03 kb and 5.16 kb) and beyond the detection thresholds of CMA and ES. Moreover, to the best of our knowledge, we have described the first prenatal instance of the association of FGF8 with holoprosencephaly and facial deformities.

CONCLUSIONS

Our analysis demonstrates the clinical value of WGS in the diagnosis of the underlying etiology of fetuses with structural abnormalities, when routine genetic tests have failed to provide a diagnosis. Additionally, the novel variants and new fetal manifestations have expanded the mutational and phenotypic spectrums of BBS9 and FGF8. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.

Identification of genetic variants and phenotypic characterization of a large cohort of patients with congenital hypopituitarism and related disorders

PURPOSE

Congenital hypopituitarism (CH) disorders are phenotypically variable. Variants in multiple genes are associated with these disorders, with variable penetrance and inheritance.

METHODS

We screened a large cohort (N = 1765) of patients with or at risk of CH using Sanger sequencing, selected according to phenotype, and conducted next-generation sequencing (NGS) in 51 families within our cohort. We report the clinical, hormonal, and neuroradiological phenotypes of patients with variants in known genes associated with CH.

RESULTS

We identified variants in 178 patients: GH1/GHRHR (51 patients of 414 screened), PROP1 (17 of 253), POU1F1 (15 of 139), SOX2 (13 of 59), GLI2 (7 of 106), LHX3/LHX4 (8 of 110), HESX1 (8 of 724), SOX3 (9 of 354), OTX2 (5 of 59), SHH (2 of 64), and TCF7L1, KAL1, FGFR1, and FGF8 (2 of 585, respectively). NGS identified 26 novel variants in 35 patients (from 24 families). Magnetic resonance imaging showed prevalent hypothalamo-pituitary abnormalities, present in all patients with PROP1, GLI2, SOX3, HESX1, OTX2, LHX3, and LHX4 variants. Normal hypothalamo-pituitary anatomy was reported in 24 of 121, predominantly those with GH1, GHRHR, POU1F1, and SOX2 variants.

CONCLUSION

We identified variants in 10% (178 of 1765) of our CH cohort. NGS has revolutionized variant identification, and careful phenotypic patient characterization has improved our understanding of CH. We have constructed a flow chart to guide genetic analysis in these patients, which will evolve upon novel gene discoveries.

The hidden hedgehog of the pituitary: hedgehog signaling in development, adulthood and disease of the hypothalamic-pituitary axis

Hedgehog signaling plays pivotal roles in embryonic development, adult homeostasis and tumorigenesis. However, its engagement in the pituitary gland has been long underestimated although Hedgehog signaling and pituitary embryogenic development are closely linked. Thus, deregulation of this signaling pathway during pituitary development results in malformation of the gland. Research of the last years further implicates a regulatory role of Hedgehog signaling in the function of the adult pituitary, because its activity is also interlinked with homeostasis, hormone production, and most likely also formation of neoplasms of the gland. The fact that this pathway can be efficiently targeted by validated therapeutic strategies makes it a promising candidate for treating pituitary diseases. We here summarize the current knowledge about the importance of Hedgehog signaling during pituitary development and review recent data that highlight the impact of Hedgehog signaling in the healthy and the diseased adult pituitary gland.

Growth hormone deficiency in a case of septo-optic-dysplasia due to SOX2 mutation: should we re-test patients during the transition period?

Gene mutations encoding transcription factors, including SOX2, have been associated with growth hormone deficiency (GHD) and abnormal pituitary development. Guidelines on GHD management in the transition period state that patients with genetic-based childhood-onset GHD can skip retesting due to a high likelihood of permanent GHD. We describe a case of septo-optic-dysplasia due to SOX2 mutation characterised by childhood-onset GHD, which showed a normal somatotropic function at the transition period. This case raises the opportunity to retest for GHD during the transition period, even in patients with a known genetic cause, in order to avoid inappropriate GH treatment.

Transcriptional Profile of the Developing Subthalamic Nucleus

The subthalamic nucleus (STN) is a small, excitatory nucleus that regulates the output of basal ganglia motor circuits. The functions of the STN and its role in the pathophysiology of Parkinson's disease are now well established. However, some basic characteristics like the developmental origin and molecular phenotype of neuronal subpopulations are still being debated. The classical model of forebrain development attributed the origin of STN within the diencephalon. Recent studies of gene expression patterns exposed shortcomings of the classical model. To accommodate these findings, the prosomeric model was developed. In this concept, STN develops within the hypothalamic primordium, which is no longer a part of the diencephalic primordium. This concept is further supported by the expression patterns of many transcription factors. It is interesting to note that many transcription factors involved in the development of the STN are also involved in the pathogenesis of neurodevelopmental disorders. Thus, the study of neurodevelopmental disorders could provide us with valuable information on the roles of these transcription factors in the development and maintenance of STN phenotype. In this review, we summarize historical theories about the developmental origin of the STN and interpret the gene expression data within the prosomeric conceptual framework. Finally, we discuss the importance of neurodevelopmental disorders for the development of the STN and its potential role in the pathophysiology of neurodevelopmental disorders.

Phosphorylation of β-catenin at Serine552 correlates with invasion and recurrence of non-functioning pituitary neuroendocrine tumours

Non-functioning pituitary tumours (NF-PitNETs) are common intracranial benign neoplasms that can exhibit aggressive behaviour by invading neighbouring structures and, in some cases, have multiple recurrences. Despite resulting in severe co-morbidities, no predictive biomarkers of recurrence have been identified for NF-PitNETs. In this study we have used high-throughput mass spectrometry-based analysis to examine the phosphorylation pattern of different subsets of NF-PitNETs. Based on histopathological, radiological, surgical and clinical features, we have grouped NF-PitNETs into non-invasive, invasive, and recurrent disease groups. Tumour recurrence was determined based on regular clinical and radiological data of patients for a mean follow-up of 10 years (SD ± 5.4 years). Phosphoproteomic analyses identified a unique phosphopeptide enrichment pattern which correlates with disease recurrence. Candidate phosphorylated proteins were validated in a large cohort of NF-PitNET patients by western blot and immunohistochemistry. We identified a cluster of 22 phosphopeptides upregulated in recurrent NF-PitNETs compared to non-invasive and invasive subgroups. We reveal significant phosphorylation of the β-catenin at Ser552 in recurrent and invasive NF-PitNETs, compared to non-invasive/non-recurrent NF-PitNET subgroup. Moreover, β-catenin pSer552 correlates with the recurrence free survival among 200 patients with NF-PitNET. Together, our results suggest that the phosphorylation status of β-catenin at Ser552 could act as potential biomarker of tumour recurrence in NF-PitNETs.

Ca2+ homeostasis maintained by TMCO1 underlies corpus callosum development via ERK signaling

Transmembrane of coiled-coil domains 1 (TMCO1) plays an important role in maintaining homeostasis of calcium (Ca²⁺) stores in the endoplasmic reticulum (ER). TMCO1-defect syndrome shares multiple features with human cerebro-facio-thoracic (CFT) dysplasia, including abnormal corpus callosum (CC). Here, we report that TMCO1 is required for the normal development of CC through sustaining Ca²⁺ homeostasis. Tmco1^-/- mice exhibit severe agenesis of CC with stalled white matter fiber bundles failing to pass across the midline. Mechanistically, the excessive Ca²⁺ signals caused by TMCO1 deficiency result in upregulation of FGFs and over-activation of ERK, leading to an excess of glial cell migration and overpopulated midline glia cells in the indusium griseum which secretes Slit2 to repulse extension of the neural fiber bundles before crossing the midline. Supportingly, using the clinical MEK inhibitors to attenuate the over-activated FGF/ERK signaling can significantly improve the CC formation in Tmco1^-/- brains. Our findings not only unravel the underlying mechanism of abnormal CC in TMCO1 defect syndrome, but also offer an attractive prevention strategy to relieve the related agenesis of CC in patients.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

Whole Exome Sequencing Points towards a Multi-Gene Synergistic Action in the Pathogenesis of Congenital Combined Pituitary Hormone Deficiency

Combined pituitary hormone deficiency (CPHD) is characterized by deficiency of growth hormone and at least one other pituitary hormone. Pathogenic variants in more than 30 genes expressed during the development of the head, hypothalamus, and/or pituitary have been identified so far to cause genetic forms of CPHD. However, the etiology of around 85% of the cases remains unknown. The aim of this study was to unveil the genetic etiology of CPHD due to congenital hypopituitarism employing whole exome sequencing (WES) in two newborn patients, initially tested and found to be negative for PROP1, LHX3, LHX4 and HESX1 pathogenic variants by Sanger sequencing and for copy number variations by MLPA. In this study, the application of WES in these CPHD newborns revealed the presence of three different heterozygous gene variants in each patient. Specifically in patient 1, the variants BMP4; p.Ala42Pro, GNRH1; p.Arg73Ter and SRA1; p.Gln32Glu, and in patient 2, the SOX9; p.Val95Ile, HS6ST1; p.Arg306Gln, and IL17RD; p.Pro566Ser were identified as candidate gene variants. These findings further support the hypothesis that CPHD constitutes an oligogenic rather than a monogenic disease and that there is a genetic overlap between CPHD and congenital hypogonadotropic hypogonadism.

Patterning of the antero-ventral mammalian brain: Lessons from holoprosencephaly comparative biology in man and mouse

Adult form and function are dependent upon the activity of specialized signaling centers that act early in development at the embryonic midline. These centers instruct the surrounding cells to adopt a positional fate and to form the patterned structures of the phylotypic embryo. Abnormalities in these processes have devastating consequences for the individual, as exemplified by holoprosencephaly in which anterior midline development fails, leading to structural defects of the brain and/or face. In the 25 years since the first association between human holoprosencephaly and the sonic hedgehog gene, a combination of human and animal genetic studies have enhanced our understanding of the genetic and embryonic causation of this congenital defect. Comparative biology has extended the holoprosencephaly network via the inclusion of gene mutations from multiple signaling pathways known to be required for anterior midline formation. It has also clarified aspects of holoprosencephaly causation, showing that it arises when a deleterious variant is present within a permissive genome, and that environmental factors, as well as embryonic stochasticity, influence the phenotypic outcome of the variant. More than two decades of research can now be distilled into a framework of embryonic and genetic causation. This framework means we are poised to move beyond our current understanding of variants in signaling pathway molecules. The challenges now at the forefront of holoprosencephaly research include deciphering how the mutation of genes involved in basic cell processes can also cause holoprosencephaly, determining the important constituents of the holoprosencephaly permissive genome, and identifying environmental compounds that promote holoprosencephaly. This article is categorized under: Congenital Diseases > Stem Cells and Development Congenital Diseases > Genetics/Genomics/Epigenetics Congenital Diseases > Molecular and Cellular Physiology Congenital Diseases > Environmental Factors.

The crucial role of model systems in understanding the complexity of cell signaling in human neurocristopathies

Animal models are useful to study the molecular, cellular, and morphogenetic mechanisms underlying normal and pathological development. Cell-based study models have emerged as an alternative approach to study many aspects of human embryonic development and disease. The neural crest (NC) is a transient, multipotent, and migratory embryonic cell population that generates a diverse group of cell types that arises during vertebrate development. The abnormal formation or development of the NC results in neurocristopathies (NCPs), which are characterized by a broad spectrum of functional and morphological alterations. The impaired molecular mechanisms that give rise to these multiphenotypic diseases are not entirely clear yet. This fact, added to the high incidence of these disorders in the newborn population, has led to the development of systematic approaches for their understanding. In this article, we have systematically reviewed the ways in which experimentation with different animal and cell model systems has improved our knowledge of NCPs, and how these advances might contribute to the development of better diagnostic and therapeutic tools for the treatment of these pathologies. This article is categorized under: Congenital Diseases > Genetics/Genomics/Epigenetics Congenital Diseases > Stem Cells and Development Congenital Diseases > Molecular and Cellular Physiology Neurological Diseases > Genetics/Genomics/Epigenetics.

Current concepts surrounding neonatal hormone therapy for boys with congenital hypogonadotropic hypogonadism

INTRODUCTION

Congenital hypogonadotropic hypogonadism (CHH) is a genetic disorder of reproduction and development, characterized by deficient gonadotropin-releasing hormone (GnRH) secretion or action, affecting 1-in-4,000-15,000 males. Micropenis and undescended testes are cardinal features of antenatal GnRH deficiency and could indicate absent minipuberty in the first postnatal months. In this review, we outline the pathophysiology and clinical consequences of absent minipuberty and its implications for optimal approaches to the endocrine management of affected boys.

AREAS COVERED

Deficient GnRH activity during fetal development and neonatal-infancy phase of minipuberty accounts for the diminished mass of Sertoli cells and seminiferous tubules among CHH males, enduring impairment of reproductive function even during gonadotropin replacement in adult life. In overcoming this obstacle, several clinical studies of neonatal gonadotropin replacement have consistently shown positive results in inducing testicular development and correcting cryptorchidism.

EXPERT OPINION

A high index of clinical suspicion, combined with hormonal testing undertaken in the postnatal period of 1-4 months, can reliably confirm or refute the diagnosis of CHH. Timely identification of CHH in affected male infants (having characteristic "red flag' developmental anomalies) opens up the possibility for gonadotropin replacement as a targeted therapy to restore the normal hormonal milieu of minipuberty. Further work is necessary in formulating optimal gonadotropin treatment regimens to be more widely adopted in clinical practice.

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.

New SHH and Known SIX3 Variants in a Series of Latin American Patients with Holoprosencephaly

Holoprosencephaly (HPE) is the failure of the embryonic forebrain to develop into 2 hemispheres promoting midline cerebral and facial defects. The wide phenotypic variability and causal heterogeneity make genetic counseling difficult. Heterozygous variants with incomplete penetrance and variable expressivity in the SHH, SIX3, ZIC2, and TGIF1 genes explain ∼25% of the known causes of nonchromosomal HPE. We studied these 4 genes and clinically described 27 Latin American families presenting with nonchromosomal HPE. Three new SHH variants and a third known SIX3 likely pathogenic variant found by Sanger sequencing explained 15% of our cases. Genotype-phenotype correlation in these 4 families and published families with identical or similar driver gene, mutated domain, conservation of residue in other species, and the type of variant explain the pathogenicity but not the phenotypic variability. Nine patients, including 2 with SHH pathogenic variants, presented benign variants of the SHH, SIX3, ZIC2, and TGIF1 genes with potential alteration of splicing, a causal proposition in need of further studies. Finding more families with the same SIX3 variant may allow further identification of genetic or environmental modifiers explaining its variable phenotypic expression.

Genetics of hypogonadotropic Hypogonadism-Human and mouse genes, inheritance, oligogenicity, and genetic counseling

Hypogonadotropic hypogonadism, which may be normosmic (nHH) or anosmic/hyposmic, known as Kallmann syndrome (KS), is due to gonadotropin-releasing hormone deficiency, which results in absent puberty and infertility. Investigation of the genetic basis of nHH/KS over the past 35 years has yielded a substantial increase in our understanding, as variants in 44 genes in OMIM account for ~50% of cases. The first genes for KS (ANOS1) and nHH (GNRHR) were followed by the discovery that FGFR1 variants may cause either nHH or KS. Associated anomalies include midline facial defects, neurologic deficits, cardiac anomalies, and renal agenesis, among others. Mouse models for all but one gene (ANOS1) generally support findings in humans. About half of the known genes implicated in nHH/KS are inherited as autosomal dominant and half are autosomal recessive, whereas only 7% are X-linked recessive. Digenic and oligogenic inheritance has been reported in 2-20% of patients, most commonly with variants in genes that may result in either nHH or KS inherited in an autosomal dominant fashion. In vitro analyses have only been conducted for both gene variants in eight cases and for one gene variant in 20 cases. Rigorous confirmation that two gene variants in the same individual cause the nHH/KS phenotype is lacking for most. Clinical diagnosis is probably best accomplished by targeted next generation sequencing of the known candidate genes with confirmation by Sanger sequencing. Elucidation of the genetic basis of nHH/KS has resulted in an enhanced understanding of this disorder, as well as normal puberty, which makes genetic diagnosis clinically relevant.

Comprehensive Identification of Pathogenic Gene Variants in Patients With Neuroendocrine Disorders

PURPOSE

Congenital hypopituitarism (CH) can present in isolation or with other birth defects. Mutations in multiple genes can cause CH, and the use of a genetic screening panel could establish the prevalence of mutations in known and candidate genes for this disorder. It could also increase the proportion of patients that receive a genetic diagnosis.

METHODS

We conducted target panel genetic screening using single-molecule molecular inversion probes sequencing to assess the frequency of mutations in known hypopituitarism genes and new candidates in Argentina. We captured genomic deoxyribonucleic acid from 170 pediatric patients with CH, either alone or with other abnormalities. We performed promoter activation assays to test the functional effects of patient variants in LHX3 and LHX4.

RESULTS

We found variants classified as pathogenic, likely pathogenic, or with uncertain significance in 15.3% of cases. These variants were identified in known CH causative genes (LHX3, LHX4, GLI2, OTX2, HESX1), in less frequently reported genes (FOXA2, BMP4, FGFR1, PROKR2, PNPLA6) and in new candidate genes (BMP2, HMGA2, HNF1A, NKX2-1).

CONCLUSION

In this work, we report the prevalence of mutations in known CH genes in Argentina and provide evidence for new candidate genes. We show that CH is a genetically heterogeneous disease with high phenotypic variation and incomplete penetrance, and our results support the need for further gene discovery for CH. Identifying population-specific pathogenic variants will improve the capacity of genetic data to predict eventual clinical outcomes.

Tangential Intrahypothalamic Migration of the Mouse Ventral Premamillary Nucleus and Fgf8 Signaling

The tuberal hypothalamic ventral premamillary nucleus (VPM) described in mammals links olfactory and metabolic cues with mating behavior and is involved in the onset of puberty. We offer here descriptive and experimental evidence on a migratory phase in the development of this structure in mice at E12.5–E13.5. Its cells originate at the retromamillary area (RM) and then migrate tangentially rostralward, eschewing the mamillary body, and crossing the molecularly distinct perimamillary band, until they reach a definitive relatively superficial ventral tuberal location. Corroborating recent transcriptomic studies reporting a variety of adult glutamatergic cell types in the VPM, and different projections in the adult, we found that part of this population heterogeneity emerges already early in development, during tangential migration, in the form of differential gene expression properties of at least 2–3 mixed populations possibly derived from subtly different parts of the RM. These partly distribute differentially in the core and shell parts of the final VPM. Since there is a neighboring acroterminal source of Fgf8, and Fgfr2 is expressed at the early RM, we evaluated a possible influence of Fgf8 signal on VPM development using hypomorphic Fgf8^neo/null embryos. These results suggested a trophic role of Fgf8 on RM and all cells migrating tangentially out of this area (VPM and the subthalamic nucleus), leading in hypomorphs to reduced cellularity after E15.5 without alteration of the migrations proper.

Effect of TO901317 on GF to promote the differentiation of human bone marrow mesenchymal stem cells into dopamine neurons on Parkinson's disease

Background:

Human bone marrow mesenchymal stem cells (hBMSCs) could differentiate into dopamine-producing cells and ameliorate behavioral deficits in Parkinson’s disease (PD) models. Liver X receptors (LXRs) are involved in the maintenance of the normal function of central nervous system myelin. Therefore, the previous work of our team has found the induction of cocktail-induced to dopaminergic (DA) phenotypes from adult rat BMSCs by using sonic hedgehog (SHH), fibroblast growth factor 8 (FGF8), basic fibroblast growth factor (bFGF), and TO901317 (an agonist of LXRs) with 87.42% of efficiency in a 6-day induction period. But we did not verify whether the induced cells had the corresponding neural function.

Methods:

Expressions of LXRα, LXRβ, and tyrosine hydroxylase (TH) were detected by immunofluorescence and western blot. Adenosine triphosphate-binding cassette transporter A1 (ABCA1) was detected by quantitative real-time PCR. The induced cells were transplanted into PD rats to study whether the induced cells are working.

Results:

The induced cells can release the dopamine transmitter; the maximum induction efficiency of differentiation of hBMSCs into DA neurons was 91.67% under conditions of combined use with TO901317 and growth factors (GF). When the induced-cells were transplanted into PD rats, the expression of TH in the striatum increased significantly, and the behavior of PD rats induced by apomorphine was significantly improved.

Conclusion:

The induced cells have the function of DA neurons and have the potential to treat PD. TO901317 promoted differentiation of hBMSCs into DA neurons, which may be related to activation of the LXR-ABCA1 signaling pathway.

Hypothalamic-pituitary organoid generation through the recapitulation of organogenesis

This paper overviews the development and differentiation of the hypothalamus and pituitary gland from embryonic stem (ES) and induced pluripotent stem (iPS) cells. It is important to replicate the developmental process in vivo to create specific cells/organoids from ES/iPS cells. We also introduce the latest findings and discuss future issues for clinical application. Neuroectodermal progenitors are induced from pluripotent stem cells by strictly removing exogenous patterning factors during the early differentiation period. The induced progenitors differentiate into rostral hypothalamic neurons, in particular magnocellular vasopressin⁺  neurons. In three-dimensional cultures, ES/iPS cells differentiate into hypothalamic neuroectoderm and nonneural head ectoderm adjacently. Rathke's pouch-like structures self-organize at the interface between the two layers and generate various endocrine cells, including corticotrophs and somatotrophs. Our next objective is to sophisticate our stepwise methodology to establish a novel transplantation treatment for hypopituitarism and apply it to developmental disease models.

Clinical delineation of an adult female patient with a rare interstitial 10q24.32q25.1 microdeletion

Interstitial deletions encompassing the 10q24.32q25.1 region are rare. Only three patients have been reported in literature to date. We describe a 44-year-old female with a 2.8 Mb microdeletion in 10q24.32q25.1. Clinical findings in this patient are delineated and compared to previously reported patients with (partly) overlapping microdeletions. Based on the few descriptions available in the literature, the major phenotypic features of microdeletion 10q24.32q25.1 seem to be profound developmental delay, severe intellectual disability, short stature, cleft lip and palate, multiple congenital malformations (brain, kidney and cardiac), ophthalmic problems and an increased risk to develop basal cell carcinoma. As far as we are aware, this is the first report of an adult patient with a 10q24.32q25.1 microdeletion in literature. Suggestions are made regarding the medical work-up for newly identified patients with a 10q24.32q25.1 microdeletion as well as for a possible interaction of the compound deletion of SUFU and FGF8 in midline craniofacial abnormalities.

Neurobiology of puberty and its disorders

Puberty, which in humans is considered to include both gonadarche and adrenarche, is the period of becoming capable of reproducing sexually and is recognized by maturation of the gonads and development of secondary sex characteristics. Gonadarche referring to growth and maturation of the gonads is fundamental to puberty since it encompasses increased gonadal steroid secretion and initiation of gametogenesis resulting from enhanced pituitary gonadotropin secretion, triggered in turn by robust pulsatile GnRH release from the hypothalamus. This chapter reviews the development of GnRH pulsatility from before birth until the onset of puberty. In humans, GnRH pulse generation is restrained during childhood and juvenile development. This prepubertal hiatus in hypothalamic activity is considered to result from a neurobiological brake imposed upon the GnRH pulse generator resident in the infundibular nucleus. Reactivation of the GnRH pulse generator initiates pubertal development. Current understanding of the genetics and physiology of the brake will be discussed, as will hypotheses proposed to account for timing the resurgence in pulsatile GnRH and initiation of puberty. The chapter ends with a discussion of disorders associated with precocious or delayed puberty with a focus on those with etiologies attributed to aberrant GnRH neuron anatomy or function. A pediatric approach to patients with pubertal disorders is provided and contemporary treatments for both precocious and delayed puberty outlined.

A nonsense variant in FGFR1: a rare cause of combined pituitary hormone deficiency

OBJECTIVES

Variants in fibroblast growth factor receptor-1 (FGFR1) may either cause isolated hypogonadotropic hypogonadism (IHH) or Kallmann syndrome (KS). Although the relationship of genes classically involved in IHH with combined pituitary hormone deficiency (CPHD) is well established, variants in FGFR1 have been presented as a rare cause of this phenotype recently.

CASE PRESENTATION

Herein, we report an adopted 16-year-old male presented with delayed puberty and micropenis. He had undergone surgery for bilateral undescended testes in childhood. He was normosmic, and the pituitary imaging was normal. However, hypogonadotropic hypogonadism and growth hormone deficiency were detected, associated with a heterozygous nonsense variant (c.1864 C>T, p.R622X) in FGFR1.

CONCLUSIONS

FGFR1 variants are among the causes of IHH and KS, which are inherited in an autosomal dominant manner and can be associated with midline defects. It should also be kept in mind that CPHD may be associated with FGFR1 variants in a subject with normal olfactory function.

Induction of Functional Hypothalamus and Pituitary Tissues From Pluripotent Stem Cells for Regenerative Medicine

The hypothalamus and pituitary have been identified to play essential roles in maintaining homeostasis. Various diseases can disrupt the functions of these systems, which can often result in serious lifelong symptoms. The current treatment for hypopituitarism involves hormone replacement therapy. However, exogenous drug administration cannot mimic the physiological changes that are a result of hormone requirements. Therefore, patients are at a high risk of severe hormone deficiency, including adrenal crisis.

Pluripotent stem cells (PSCs) self-proliferate and differentiate into all types of cells. The generation of endocrine tissues from PSCs has been considered as another new treatment for hypopituitarism. Our colleagues established a 3-dimensional (3D) culture method for embryonic stem cells (ESCs). In this culture, the ESC-derived aggregates exhibit self-organization and spontaneous formation of highly ordered patterning. Recent results have shown that strict removal of exogenous patterning factors during early differentiation efficiently induces rostral hypothalamic progenitors from mouse ESCs. These hypothalamic progenitors generate vasopressinergic neurons, which release neuropeptides upon exogenous stimulation.

Subsequently, we reported adenohypophysis tissue self-formation in 3D cultures of mouse ESCs. The ESCs were found to differentiate into both nonneural oral ectoderm and hypothalamic neuroectoderm in adjacent layers. Interactions between the 2 tissues appear to be critically important for in vitro induction of a Rathke’s pouch-like developing embryo. Various endocrine cells were differentiated from nonneural ectoderm. The induced corticotrophs efficiently secreted adrenocorticotropic hormone when engrafted in vivo, which rescued hypopituitary hosts.

For future regenerative medicine, generation of hypothalamic and pituitary tissues from human PSCs is necessary. We and other groups succeeded in establishing a differentiation method with the use of human PSCs. Researchers could use these methods for models of human diseases to elucidate disease pathology or screen potential therapeutics.

Developmental Genes and Malformations in the Hypothalamus

The hypothalamus is a heterogeneous rostral forebrain region that regulates physiological processes essential for survival, energy metabolism, and reproduction, mainly mediated by the pituitary gland. In the updated prosomeric model, the hypothalamus represents the rostralmost forebrain, composed of two segmental regions (terminal and peduncular hypothalamus), which extend respectively into the non-evaginated preoptic telencephalon and the evaginated pallio-subpallial telencephalon. Complex genetic cascades of transcription factors and signaling molecules rule their development. Alterations of some of these molecular mechanisms acting during forebrain development are associated with more or less severe hypothalamic and pituitary dysfunctions, which may be associated with brain malformations such as holoprosencephaly or septo-optic dysplasia. Studies on transgenic mice with mutated genes encoding critical transcription factors implicated in hypothalamic-pituitary development are contributing to understanding the high clinical complexity of these pathologies. In this review article, we will analyze first the complex molecular genoarchitecture of the hypothalamus resulting from the activity of previous morphogenetic signaling centers and secondly some malformations related to alterations in genes implicated in the development of the hypothalamus.

Disrupted Hypothalamo-Pituitary Axis in Association With Reduced SHH Underlies the Pathogenesis of NOTCH-Deficiency

CONTEXT

In human, Sonic hedgehog (SHH) haploinsufficiency is the predominant cause of holoprosencephaly, a structural malformation of the forebrain midline characterized by phenotypic heterogeneity and incomplete penetrance. The NOTCH signaling pathway has recently been associated with holoprosencephaly in humans, but the precise mechanism involving NOTCH signaling during early brain development remains unknown.

OBJECTIVE

The aim of this study was to evaluate the relationship between SHH and NOTCH signaling to determine the mechanism by which NOTCH dysfunction could cause midline malformations of the forebrain.

DESIGN

In this study, we have used a chemical inhibition approach in the chick model and a genetic approach in the mouse model. We also reported results obtained from the clinical diagnosis of a cohort composed of 141 holoprosencephaly patients.

RESULTS

We demonstrated that inhibition of NOTCH signaling in chick embryos as well as in mouse embryos induced a specific downregulation of SHH in the anterior hypothalamus. Our data in the mouse also revealed that the pituitary gland was the most sensitive tissue to Shh insufficiency and that haploinsufficiency of the SHH and NOTCH signaling pathways synergized to produce a malformed pituitary gland. Analysis of a large holoprosencephaly cohort revealed that some patients possessed multiple heterozygous mutations in several regulators of both pathways.

CONCLUSIONS

These results provided new insights into molecular mechanisms underlying the extreme phenotypic variability observed in human holoprosencephaly. They showed how haploinsufficiency of the SHH and NOTCH activity could contribute to specific congenital hypopituitarism that was associated with a sella turcica defect.

Haploinsufficiency of NKX2-1 in Brain-Lung-Thyroid Syndrome with Additional Multiple Pituitary Dysfunction

INTRODUCTION

Heterozygous mutations or haploinsufficiency of NKX2-1 are associated with the brain-lung-thyroid syndrome incorporating primary hypothyroidism, respiratory distress, and neurological disturbances.

CASE PRESENTATION

We report a patient presenting in the neonatal period with multiple pituitary hormone deficiency including central hypothyroidism and hypoadrenalism, growth hormone deficiency, undetectable gonadotrophins, and a small anterior pituitary on MRI. CGH microarray revealed haploinsufficiency for NKX2.1 and during subsequent follow-up, she has exhibited the classic triad of brain-lung-thyroid syndrome with undetectable tissue on thyroid ultrasonography. Whilst the role of NKX2-1 is well described in murine pituitary development, this report constitutes the first description of multiple pituitary dysfunction in humans associated with the syndrome and haploinsufficiency NKX2-1.

CONCLUSION

The report highlights a potential need for pituitary screening in patients with established brain-lung-thyroid syndrome and implicates NKX2.1 in human pituitary disease.

The Molecular Basis of Congenital Hypopituitarism and Related Disorders

CONTEXT

Congenital hypopituitarism (CH) is characterized by the presence of deficiencies in one or more of the 6 anterior pituitary (AP) hormones secreted from the 5 different specialized cell types of the AP. During human embryogenesis, hypothalamo-pituitary (HP) development is controlled by a complex spatio-temporal genetic cascade of transcription factors and signaling molecules within the hypothalamus and Rathke's pouch, the primordium of the AP.

EVIDENCE ACQUISITION

This mini-review discusses the genes and pathways involved in HP development and how mutations of these give rise to CH. This may present in the neonatal period or later on in childhood and may be associated with craniofacial midline structural abnormalities such as cleft lip/palate, visual impairment due to eye abnormalities such as optic nerve hypoplasia (ONH) and microphthalmia or anophthalmia, or midline forebrain neuroradiological defects including agenesis of the septum pellucidum or corpus callosum or the more severe holoprosencephaly.

EVIDENCE SYNTHESIS

Mutations give rise to an array of highly variable disorders ranging in severity. There are many known causative genes in HP developmental pathways that are routinely screened in CH patients; however, over the last 5 years this list has rapidly increased due to the identification of variants in new genes and pathways of interest by next-generation sequencing.

CONCLUSION

The majority of patients with these disorders do not have an identified molecular basis, often making management challenging. This mini-review aims to guide clinicians in making a genetic diagnosis based on patient phenotype, which in turn may impact on clinical management.

Genetics of congenital hypogonadotropic hypogonadism: peculiarities and phenotype of an oligogenic disease

A genetic basis of congenital isolated hypogonadotropic hypogonadism (CHH) can be defined in almost 50% of cases, albeit not necessarily the complete genetic basis. Next-generation sequencing (NGS) techniques have led to the discovery of a great number of loci, each of which has illuminated our understanding of human gonadotropin-releasing hormone (GnRH) neurons, either in respect of their embryonic development or their neuroendocrine regulation as the "pilot light" of human reproduction. However, because each new gene linked to CHH only seems to underpin another small percentage of total patient cases, we are still far from achieving a comprehensive understanding of the genetic basis of CHH. Patients have generally not benefited from advances in genetics in respect of novel therapies. In most cases, even genetic counselling is limited by issues of apparent variability in expressivity and penetrance that are likely underpinned by oligogenicity in respect of known and unknown genes. Robust genotype-phenotype relationships can generally only be established for individuals who are homozygous, hemizygous or compound heterozygotes for the same gene of variant alleles that are predicted to be deleterious. While certain genes are purely associated with normosmic CHH (nCHH) some purely with the anosmic form (Kallmann syndrome-KS), other genes can be associated with both nCHH and KS-sometimes even within the same kindred. Even though the anticipated genetic overlap between CHH and constitutional delay in growth and puberty (CDGP) has not materialised, previously unanticipated genetic relationships have emerged, comprising conditions of combined (or multiple) pituitary hormone deficiency (CPHD), hypothalamic amenorrhea (HA) and CHARGE syndrome. In this review, we report the current evidence in relation to phenotype and genetic peculiarities regarding 60 genes whose loss-of-function variants can disrupt the central regulation of reproduction at many levels: impairing GnRH neurons migration, differentiation or activation; disrupting neuroendocrine control of GnRH secretion; preventing GnRH neuron migration or function and/or gonadotropin secretion and action.

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.

Altered GLI3 and FGF8 signaling underlies acrocallosal syndrome phenotypes in Kif7 depleted mice

Acrocallosal syndrome (ACLS) is a rare genetic disorder characterized by agenesis or hypoplasia of corpus callosum (CC), polydactyly, craniofacial dysmorphism and severe intellectual deficiency. We previously identified KIF7, a key ciliary component of the Sonic hedgehog (SHH) pathway, as being a causative gene for this syndrome, thus including ACLS in the group of ciliopathies. In both humans and mice, KIF7 depletion leads to abnormal GLI3 processing and over-activation of SHH target genes. To understand the pathological mechanisms involved in CC defects in this syndrome, we took advantage of a previously described Kif7-/- mouse model to demonstrate that in addition to polydactyly and neural tube closure defects, these mice present CC agenesis with characteristic Probst bundles, thus recapitulating major ACLS features. We show that CC agenesis in these mice is associated with specific patterning defects of the cortical septum boundary leading to altered distribution of guidepost cells required to guide the callosal axons through the midline. Furthermore, by crossing Kif7-/- mice with Gli3Δ699 mice exclusively producing the repressive isoform of GLI3 (GLI3R), we demonstrate that decreased GLI3R signaling is fully responsible for the ACLS features in these mice, as all phenotypes are rescued by increasing GLI3R activity. Moreover, we show that increased FGF8 signaling is responsible in part for CC defects associated to KIF7 depletion, as modulating FGF8 signaling rescued CC formation anteriorly in Kif7-/- mice. Taken together our data demonstrate that ACLS features rely on defective GLI3R and FGF8 signaling.

Congenital Hypopituitarism During the Neonatal Period: Epidemiology, Pathogenesis, Therapeutic Options, and Outcome

Introduction: Congenital hypopituitarism (CH) is characterized by a deficiency of one or more pituitary hormones. The pituitary gland is a central regulator of growth, metabolism, and reproduction. The anterior pituitary produces and secretes growth hormone (GH), adrenocorticotropic hormone, thyroid-stimulating hormone, follicle-stimulating hormone, luteinizing hormone, and prolactin. The posterior pituitary hormone secretes antidiuretic hormone and oxytocin. Epidemiology: The incidence is 1 in 4,000-1 in 10,000. The majority of CH cases are sporadic; however, a small number of familial cases have been identified. In the latter, a molecular basis has frequently been identified. Between 80-90% of CH cases remain unsolved in terms of molecular genetics. Pathogenesis: Several transcription factors and signaling molecules are involved in the development of the pituitary gland. Mutations in any of these genes may result in CH including HESX1, PROP1, POU1F1, LHX3, LHX4, SOX2, SOX3, OTX2, PAX6, FGFR1, GLI2, and FGF8. Over the last 5 years, several novel genes have been identified in association with CH, but it is likely that many genes remain to be identified, as the majority of patients with CH do not have an identified mutation. Clinical manifestations: Genotype-phenotype correlations are difficult to establish. There is a high phenotypic variability associated with different genetic mutations. The clinical spectrum includes severe midline developmental disorders, hypopituitarism (in isolation or combined with other congenital abnormalities), and isolated hormone deficiencies. Diagnosis and treatment: Key investigations include MRI and baseline and dynamic pituitary function tests. However, dynamic tests of GH secretion cannot be performed in the neonatal period, and a diagnosis of GH deficiency may be based on auxology, MRI findings, and low growth factor concentrations. Once a hormone deficit is confirmed, hormone replacement should be started. If onset is acute with hypoglycaemia, cortisol deficiency should be excluded, and if identified this should be rapidly treated, as should TSH deficiency. This review aims to give an overview of CH including management of this complex condition.

Update on new GH-IGF axis genetic defects

The somatotropic axis is the main hormonal regulator of growth. Growth hormone (GH), also known as somatotropin, and insulin-like growth factor 1 (IGF-1) are the key components of the somatotropic axis. This axis has been studied for a long time and the knowledge of how some molecules could promote or impair hormones production and action has been growing over the last decade. The enhancement of large-scale sequencing techniques has expanded the spectrum of known genes and several other candidate genes that could affect the GH-IGF1-bone pathway. To date, defects in more than forty genes were associated with an impairment of the somatotropic axis. These defects can affect from the secretion of GH to the bioavailability and action of IGF-1. Affected patients present a large heterogeneous group of conditions associated with growth retardation. In this review, we focus on the description of the GH-IGF axis genetic defects reported in the last decade. Arch Endocrinol Metab. 2019;63(6):608-17.

TET1 regulates fibroblast growth factor 8 transcription in gonadotropin releasing hormone neurons

Fibroblast growth factor 8 (FGF8) is a potent morphogen that regulates the ontogenesis of gonadotropin-releasing hormone (GnRH) neurons, which control the hypothalamus-pituitary-gonadal (HPG) axis, and therefore reproductive success. Indeed, FGF8 and FGFR1 deficiency severely compromises vertebrate reproduction in mice and humans and is associated with Kallmann Syndrome (KS), a congenital disease characterized by hypogonadotropic hypogonadism associated with anosmia. Our laboratory demonstrated that FGF8 signaling through FGFR1, both of which are KS-related genes, is necessary for proper GnRH neuron development in mice and humans. Here, we investigated the possibility that non-genetic factors, such as the epigenome, may contribute to KS onset. For this purpose, we developed an embryonic explant model, utilizing the mouse olfactory placode (OP), the birthplace of GnRH neurons. We show that TET1, which converts 5-methylcytosine residues (5mC) to 5-hydroxymethylated cytosines (5hmC), controls transcription of Fgf8 during GnRH neuron ontogenesis. Through MeDIP and ChIP RT-qPCR we found that TET1 bound to specific CpG islands on the Fgf8 promoter. We found that the temporal expression of Fgf8 correlates with not only TET1 binding, but also with 5hmC enrichment. siRNA knockdown of Tet1 reduced Fgf8 and Fgfr1 mRNA expression. During this time period, Fgf8 also switched histone status, most likely via recruitment of EZH2, a major component of the polycomb repressor complex-2 (PRC2) at E13.5. Together, these studies underscore the significance of epigenetics and chromatin modifications to temporally regulated genes involved in KS.

Septo-optic dysplasia caused by a novel FLNA splice site mutation: a case report

Background

Septo-optic dysplasia (SOD), also known as de-Morsier syndrome, is a rare disorder characterized by any combination of optic nerve hypoplasia, pituitary gland hypoplasia, and midline abnormalities of the brain including absence of the septum pellucidum and corpus callosum dysgenesis. The variable presentation of SOD includes visual, neurologic, and/or hypothalamic-pituitary endocrine defects. The unclear aetiology of a large proportion of SOD cases underscores the importance of identifying novel SOD-associated genes.

Case presentation

To identify the disease-causing gene in a male infant with neonatal hypoglycaemia, dysmorphic features, and hypoplasia of the optic nerve and corpus callosum, we designed a targeted next-generation sequencing panel for brain morphogenesis defects. We identified a novel hemizygous deletion, c.6355 + 4_6355 + 5delAG, in intron 38 of the FLNA gene that the patient had inherited from his mother. cDNA studies showed that this variant results in the production of 3 aberrant FLNA transcripts, the most abundant of which results in retention of intron 38 of FLNA.

Conclusions

We report for the first time a case of early-onset SOD associated with a mutation in the FLNA gene. This finding broadens the spectrum of genetic causes of this rare disorder and expands the phenotypic spectrum of the FLNA gene.

Loss-of-function mutations in FGF8 can be independent risk factors for holoprosencephaly

The utilization of next generation sequencing has been shown to accelerate gene discovery in human disease. However, our confidence in the correct disease-associations of rare variants continues to depend on functional analysis. Here, we employ a sensitive assay of human FGF8 variants in zebrafish to demonstrate that the spectrum of isoforms of FGF8 produced by alternative splicing can provide key insights into the genetic susceptibility to human malformations. In addition, we describe novel mutations in the FGF core structure that have both subtle and profound effects on ligand posttranslational processing and biological activity. Finally, we solve a case of apparent digenic inheritance of novel variants in SHH and FGF8, two genes known to functionally coregulate each other in the developing forebrain, as a simpler case of FGF8 diminished function.

Central adrenal insufficiency in children and adolescents

Central adrenal insufficiency (CAI) is a life-threatening condition caused by either pituitary disease (secondary adrenal insufficiency) or impaired hypothalamic function with inadequate CRH production (tertiary adrenal insufficiency). ACTH deficiency may be isolated or, more frequently, occur in conjunction with other pituitary hormone deficiencies and midline defects. Genetic mutations of the TBX19 causing isolated CAI are rare but a number of genes encoding transcription factors involved in hypothalamic-pituitary gland development, as well as other genes including POMC and PC1, are associated with ACTH deficiency. CAI is frequently identified in congenital, malformative, genetic, and epigenetic syndromes as well as in several acquired conditions of different etiologies. The signs and symptoms vary considerably and depend on the age of onset and the number and severity of associated pituitary defects. They may include hypoglycemia, lethargy, apnea, poor feeding, prolonged cholestatic jaundice, jitteriness, seizures, and sepsis in the neonate, or nonspecific signs such as fatigue, hypotension, vomiting and hyponatremia without hyperkalemia in children. The diagnosis of CAI relies on the measurement of morning cortisol concentrations along with dynamic test for cortisol release with different stimulating agents. Early recognition of CAI and its correct management are mandatory in order to avoid both morbidity and mortality in affected neonates, children and adolescents.

Molecular testing in holoprosencephaly

Holoprosencephaly (HPE) is a structural brain anomaly characterized by failure of the forebrain to separate during early embryogenesis. Both genetic and environmental etiologies of HPE have been discovered over the last three decades. Traditionally, the genetic workup for HPE has been a karyotype, chromosomal microarray, and/or Sanger sequencing of select genes. The recent increased availability of next-generation sequencing has changed the molecular diagnostic landscape for HPE, associating new genes with this disorder such as FGFR1. We conducted a systematic review of the medical literature for the molecular testing of HPE for studies published in the last 20 years. We also queried known commercial diagnostic laboratories and used information on their websites to construct a list of available commercial testing. Our group released its first recommendations in 2010 and this update incorporates the technology shifts and gene discoveries over the last decade. These recommendations provide a guide for genetic diagnosis of HPE, which is paramount for patients and their families for prognosis, treatment, and genetic counseling.

Neurocristopathies: New insights 150 years after the neural crest discovery

The neural crest (NC) is a transient, multipotent and migratory cell population that generates an astonishingly diverse array of cell types during vertebrate development. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others. Neurocristopathies (NCP) are a class of pathologies occurring in vertebrates, especially in humans that result from the abnormal specification, migration, differentiation or death of neural crest cells during embryonic development. Various pigment, skin, thyroid and hearing disorders, craniofacial and heart abnormalities, malfunctions of the digestive tract and tumors can also be considered as neurocristopathies. In this review we revisit the current classification and propose a new way to classify NCP based on the embryonic origin of the affected tissues, on recent findings regarding the molecular mechanisms that drive NC formation, and on the increased complexity of current molecular embryology techniques.

Recent advances in understanding inheritance of holoprosencephaly

Holoprosencephaly (HPE) is a complex genetic disorder of the developing forebrain characterized by high phenotypic and genetic heterogeneity. HPE was initially defined as an autosomal dominant disease, but recent research has shown that its mode of transmission is more complex. The past decade has witnessed rapid development of novel genetic technologies and significant progresses in clinical studies of HPE. In this review, we recapitulate genetic epidemiological studies of the largest European HPE cohort and summarize the novel genetic discoveries of HPE based on recently developed diagnostic methods. Our main purpose is to present different inheritance patterns that exist for HPE with a particular emphasis on oligogenic inheritance and its implications in genetic counseling.

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.

Astroglial-Mediated Remodeling of the Interhemispheric Midline Is Required for the Formation of the Corpus Callosum

The corpus callosum is the major axon tract that connects and integrates neural activity between the two cerebral hemispheres. Although ∼1:4,000 children are born with developmental absence of the corpus callosum, the primary etiology of this condition remains unknown. Here, we demonstrate that midline crossing of callosal axons is dependent upon the prior remodeling and degradation of the intervening interhemispheric fissure. This remodeling event is initiated by astroglia on either side of the interhemispheric fissure, which intercalate with one another and degrade the intervening leptomeninges. Callosal axons then preferentially extend over these specialized astroglial cells to cross the midline. A key regulatory step in interhemispheric remodeling is the differentiation of these astroglia from radial glia, which is initiated by Fgf8 signaling to downstream Nfi transcription factors. Crucially, our findings from human neuroimaging studies reveal that developmental defects in interhemispheric remodeling are likely to be a primary etiology underlying human callosal agenesis.

Canonical WNT Signaling Regulates the Pituitary Organizer and Pituitary Gland Formation

The pituitary organizer is a domain within the ventral diencephalon that expresses Bmp4, Fgf8, and Fgf10, which induce the formation of the pituitary precursor, Rathke's pouch, from the oral ectoderm. The WNT signaling pathway regulates this pituitary organizer such that loss of Wnt5a leads to an expansion of the pituitary organizer and an enlargement of Rathke's pouch. WNT signaling is classified into canonical signaling, which is mediated by β-CATENIN, and noncanonical signaling, which operates independently of β-CATENIN. WNT5A is typically classified as a noncanonical WNT; however, other WNT family members are expressed in the ventral diencephalon and nuclear localized β-CATENIN is observed in the ventral diencephalon. Therefore, we sought to determine whether canonical WNT signaling is necessary for regulation of pituitary organizer function. Using a conditional loss-of-function approach, we deleted β-catenin within the mouse ventral diencephalon. Mutant embryos have a smaller Rathke's pouch, resulting from a reduced pituitary organizer, especially Fgf8. This result suggests that canonical WNT signaling promotes pituitary organizer function, instead of inhibiting it. To test this hypothesis, we stimulated canonical WNT signaling in the ventral diencephalon using an inducible gain-of-function allele of β-catenin and found that stimulating canonical WNT signaling expands the domain of Fgf8 and results in a dysmorphic Rathke's pouch. These results demonstrate that canonical WNT signaling in the ventral diencephalon is necessary for proper expression of pituitary organizer genes and suggests that a balance of both canonical and noncanonical WNT signaling is necessary to ensure proper formation of Rathke's pouch.

Genetics of Diabetes Insipidus

Diabetes insipidus is a disease characterized by polyuria and polydipsia due to inadequate release of arginine vasopressin from the posterior pituitary gland (neurohypophyseal diabetes insipidus) or due to arginine vasopressin insensitivity by the renal distal tubule, leading to a deficiency in tubular water reabsorption (nephrogenic diabetes insipidus). This article reviews the genetics of diabetes insipidus in the context of its diagnosis, clinical presentation, and therapy.

Six3 dosage mediates the pathogenesis of holoprosencephaly

Holoprosencephaly (HPE) is defined as the incomplete separation of the two cerebral hemispheres. The pathology of HPE is variable and, based on the severity of the defect, HPE is divided into alobar, semilobar, and lobar. Using a novel hypomorphic Six3 allele, we demonstrate in mice that variability in Six3 dosage results in different HPE phenotypes. Furthermore, we show that whereas the semilobar phenotype results from severe downregulation of Shh expression in the rostral diencephalon ventral midline, the alobar phenotype is caused by downregulation of Foxg1 expression in the anterior neural ectoderm. Consistent with these results, in vivo activation of the Shh signaling pathway rescued the semilobar phenotype but not the alobar phenotype. Our findings show that variations in Six3 dosage result in different forms of HPE.

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.

Mouse Models of Gonadotrope Development

The pituitary gonadotrope is central to reproductive function. Gonadotropes develop in a systematic process dependent on signaling factors secreted from surrounding tissues and those produced within the pituitary gland itself. These signaling pathways are important for stimulating specific transcription factors that ultimately regulate the expression of genes and define gonadotrope identity. Proper gonadotrope development and ultimately gonadotrope function are essential for normal sexual maturation and fertility. Understanding the mechanisms governing differentiation programs of gonadotropes is important to improve treatment and molecular diagnoses for patients with gonadotrope abnormalities. Much of what is known about gonadotrope development has been elucidated from mouse models in which important factors contributing to gonadotrope development and function have been deleted, ectopically expressed, or modified. This chapter will focus on many of these mouse models and their contribution to our current understanding of gonadotrope development.