OTX2 loss of function mutation causes anophthalmia and combined pituitary hormone deficiency with a small anterior and ectopic posterior pituitary

The Genetics of Chiari 1 Malformation

Chiari malformation type 1 (CM1) is a structural defect that involves the herniation of the cerebellar tonsils through the foramen magnum, causing mild to severe neurological symptoms. Little is known about the molecular and developmental mechanisms leading to its pathogenesis, prompting current efforts to elucidate genetic drivers. Inherited genetic disorders are reported in 2-3% of CM1 patients; however, CM1, including familial forms, is predominantly non-syndromic. Recent work has focused on identifying CM1-asscoiated variants through the study of both familial cases and de novo mutations using exome sequencing. This article aims to review the current understanding of the genetics of CM1. We discuss three broad classes of CM1 based on anatomy and link them with genetic lesions, including posterior fossa-linked, macrocephaly-linked, and connective tissue disorder-linked CM1. Although the genetics of CM1 are only beginning to be understood, we anticipate that additional studies with diverse patient populations, tissue types, and profiling technologies will reveal new insights in the coming years.

Perineuronal nets' role in metabolism

Perineuronal nets (PNNs), specialized extracellular matrix (ECM) structures that envelop neurons, have recently been recognized as key players in the regulation of metabolism. This review explores the growing body of knowledge concerning PNNs and their role in metabolic control, drawing insights from recent research and relevant studies. The pivotal role of PNNs in the context of energy balance and whole body blood glucose is examined. This review also highlights novel findings, including the effects of astroglia, microglia, sex and gonadal hormones, nutritional regulation, circadian rhythms, and age on PNNs dynamics. These findings illuminate the complex and multifaceted role of PNNs in metabolic health.

14q22.3 duplication including OTX2 in a girl with medulloblastoma: A case report with literature review

Orthodenticle homeobox 2 (OTX2) is a known oncogenic driver of medulloblastoma. Germline duplication of 14q22.3 including OTX2 is a rare condition reported in patients with combined pituitary hormone deficiency, oculo-auriculo-vertebral spectrum, and hemifacial microsomia. There has been one previously published case of a patient carrying a 14q22.3 duplication that included OTX2 with hemifacial microsomia who also developed medulloblastoma. Here, we present a case of a 6-year-old girl with a history of delayed development who was diagnosed with medulloblastoma. Genetic evaluations revealed that she inherited a germline duplication of 14q22.3, which included OTX2. This genetic alteration was passed down from her mother, who also had a history of delayed development. Results from other genetic testing, including exome sequencing, fragile X syndrome, and mtDNA testing, were negative/normal. This is the second report of a 14q22.3 duplication that included OTX2 in a patient with medulloblastoma. Further studies are necessary to establish a clear association.

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.

OTX Genes in Adult Tissues

OTX homeobox genes have been extensively studied for their role in development, especially in neuroectoderm formation. Recently, their expression has also been reported in adult physiological and pathological tissues, including retina, mammary and pituitary glands, sinonasal mucosa, in several types of cancer, and in response to inflammatory, ischemic, and hypoxic stimuli. Reactivation of OTX genes in adult tissues supports the notion of the evolutionary amplification of functions of genes by varying their temporal expression, with the selection of homeobox genes from the "toolbox" to drive or contribute to different processes at different stages of life. OTX involvement in pathologies points toward these genes as potential diagnostic and/or prognostic markers as well as possible therapeutic targets.

Disease-causing mutations in genes encoding transcription factors critical for photoreceptor development

Photoreceptor development of the vertebrate visual system is controlled by a complex transcription regulatory network. OTX2 is expressed in the mitotic retinal progenitor cells (RPCs) and controls photoreceptor genesis. CRX that is activated by OTX2 is expressed in photoreceptor precursors after cell cycle exit. NEUROD1 is also present in photoreceptor precursors that are ready to specify into rod and cone photoreceptor subtypes. NRL is required for the rod fate and regulates downstream rod-specific genes including the orphan nuclear receptor NR2E3 which further activates rod-specific genes and simultaneously represses cone-specific genes. Cone subtype specification is also regulated by the interplay of several transcription factors such as THRB and RXRG. Mutations in these key transcription factors are responsible for ocular defects at birth such as microphthalmia and inherited photoreceptor diseases such as Leber congenital amaurosis (LCA), retinitis pigmentosa (RP) and allied dystrophies. In particular, many mutations are inherited in an autosomal dominant fashion, including the majority of missense mutations in CRX and NRL. In this review, we describe the spectrum of photoreceptor defects that are associated with mutations in the above-mentioned transcription factors, and summarize the current knowledge of molecular mechanisms underlying the pathogenic mutations. At last, we deliberate the outstanding gaps in our understanding of the genotype-phenotype correlations and outline avenues for future research of the treatment strategies.

Novel OTX2 loss of function variant associated with congenital hypopituitarism without eye abnormalities

OBJECTIVES

The normal development of the pituitary gland requires multiple induction signals and transcription factors encoded by more than 30 genes, including OTX2. OTX2 mutations have been described with eye abnormalities and variable congenital hypopituitarism, but rarely with hypopituitarism without ocular manifestations.

CASE PRESENTATION

We report a girl with hypopituitarism associated with pituitary hypoplasia and pituitary stalk atrophy, without ocular manifestations. NGS revealed a novel heterozygous mutation in OTX2 c.426dupC:p.(Ser143Leufs*2).

CONCLUSIONS

Mutations in the transcription factor OTX2 have been associated with ocular, craniofacial, and pituitary development anomalies. Here we describe a novel mutation in OTX2 associated with hypopituitarism without an ocular phenotype.

Genetic Regulation of Vertebrate Forebrain Development by Homeobox Genes

Forebrain development in vertebrates is regulated by transcription factors encoded by homeobox, bHLH and forkhead gene families throughout the progressive and overlapping stages of neural induction and patterning, regional specification and generation of neurons and glia from central nervous system (CNS) progenitor cells. Moreover, cell fate decisions, differentiation and migration of these committed CNS progenitors are controlled by the gene regulatory networks that are regulated by various homeodomain-containing transcription factors, including but not limited to those of the Pax (paired), Nkx, Otx (orthodenticle), Gsx/Gsh (genetic screened), and Dlx (distal-less) homeobox gene families. This comprehensive review outlines the integral role of key homeobox transcription factors and their target genes on forebrain development, focused primarily on the telencephalon. Furthermore, links of these transcription factors to human diseases, such as neurodevelopmental disorders and brain tumors are provided.

Identification of a novel de novo variant in OTX2 in a patient with congenital microphthalmia using targeted next-generation sequencing followed by prenatal diagnosis

BACKGROUND

Next-generation sequencing has been proven to be a reliable method for the detection of genetic causes in heterogeneous ocular disorders. In this report an NGS-based diagnostic approach was taken to uncover the genetic etiology in a patient with coloboma and microphthalmia, a highly heterogeneous disease with intrafamilial phenotypic variability.

MATERIALS AND METHODS

Next generation sequencing using a targeted panel of 316 genes, was carried out in the proband. Prioritized variants were then identified and confirmed using Sanger sequencing. Prenatal diagnosis of the detected variant was then performed in the family.

RESULTS

A novel de novo frameshift variant c.157_164delTTCACTCG (p.Phe53fs) in OTX2, leading to a truncated protein, was identified. Prenatal diagnosis identified the same variant in the fetus.

CONCLUSIONS

This report demonstrates the importance of genetic counseling and underscores the efficiency and effectiveness of targeted NGS as a means of detecting variants in inherited eye disorders.

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.

The phenotypic spectrum associated with OTX2 mutations in humans

Objective

The transcription factor OTX2 is implicated in ocular, craniofacial, and pituitary development.

Design

We aimed to establish the contribution of OTX2 mutations in congenital hypopituitarism patients with/without eye abnormalities, study functional consequences, and establish OTX2 expression in the human brain, with a view to investigate the mechanism of action.

Methods

We screened patients from the UK (n = 103), international centres (n = 24), and Brazil (n = 282); 145 were within the septo-optic dysplasia spectrum, and 264 had no eye phenotype. Transactivation ability of OTX2 variants was analysed in murine hypothalamic GT1-7 neurons. In situ hybridization was performed on human embryonic brain sections. Genetically engineered mice were generated with a series of C-terminal OTX2 variants.

Results

Two chromosomal deletions and six haploinsufficient mutations were identified in individuals with eye abnormalities; an affected relative of one patient harboured the same mutation without an ocular phenotype. OTX2 truncations led to significant transactivation reduction. A missense variant was identified in another patient without eye abnormalities; however, studies revealed it was most likely not causative. In the mouse, truncations proximal to aa219 caused anophthalmia, while distal truncations and the missense variant were tolerated. During human embryogenesis, OTX2 was expressed in the posterior pituitary, retina, ear, thalamus, choroid plexus, and partially in the hypothalamus, but not in the anterior pituitary.

Conclusions

OTX2 mutations are rarely associated with hypopituitarism in isolation without eye abnormalities, and may be variably penetrant, even within the same pedigree. Our data suggest that the endocrine phenotypes in patients with OTX2 mutations are of hypothalamic origin.

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.

Animal and cellular models of microphthalmia

Microphthalmia is a rare developmental eye disorder affecting 1 in 7000 births. It is defined as a small (axial length ⩾2 standard deviations below the age-adjusted mean) underdeveloped eye, caused by disruption of ocular development through genetic or environmental factors in the first trimester of pregnancy. Clinical phenotypic heterogeneity exists amongst patients with varying levels of severity, and associated ocular and systemic features. Up to 11% of blind children are reported to have microphthalmia, yet currently no treatments are available. By identifying the aetiology of microphthalmia and understanding how the mechanisms of eye development are disrupted, we can gain a better understanding of the pathogenesis. Animal models, mainly mouse, zebrafish and Xenopus, have provided extensive information on the genetic regulation of oculogenesis, and how perturbation of these pathways leads to microphthalmia. However, differences exist between species, hence cellular models, such as patient-derived induced pluripotent stem cell (iPSC) optic vesicles, are now being used to provide greater insights into the human disease process. Progress in 3D cellular modelling techniques has enhanced the ability of researchers to study interactions of different cell types during eye development. Through improved molecular knowledge of microphthalmia, preventative or postnatal therapies may be developed, together with establishing genotype-phenotype correlations in order to provide patients with the appropriate prognosis, multidisciplinary care and informed genetic counselling. This review summarises some key discoveries from animal and cellular models of microphthalmia and discusses how innovative new models can be used to further our understanding in the future.

Plain language summary

Animal and Cellular Models of the Eye Disorder, Microphthalmia (Small Eye) Microphthalmia, meaning a small, underdeveloped eye, is a rare disorder that children are born with. Genetic changes or variations in the environment during the first 3 months of pregnancy can disrupt early development of the eye, resulting in microphthalmia. Up to 11% of blind children have microphthalmia, yet currently no treatments are available. By understanding the genes necessary for eye development, we can determine how disruption by genetic changes or environmental factors can cause this condition. This helps us understand why microphthalmia occurs, and ensure patients are provided with the appropriate clinical care and genetic counselling advice. Additionally, by understanding the causes of microphthalmia, researchers can develop treatments to prevent or reduce the severity of this condition. Animal models, particularly mice, zebrafish and frogs, which can also develop small eyes due to the same genetic/environmental changes, have helped us understand the genes which are important for eye development and can cause birth eye defects when disrupted. Studying a patient's own cells grown in the laboratory can further help researchers understand how changes in genes affect their function. Both animal and cellular models can be used to develop and test new drugs, which could provide treatment options for patients living with microphthalmia. This review summarises the key discoveries from animal and cellular models of microphthalmia and discusses how innovative new models can be used to further our understanding in the future.

Copy Number Variants Contributing to Combined Pituitary Hormone Deficiency

Combined pituitary hormone deficiency represents a disorder with complex etiology. For many patients, causes of the disease remain unexplained, despite usage of advanced genetic testing. Although major and common transcription factors were identified two decades ago, we still struggle with identification of rare inborn factors contributing to pituitary function. In this report, we follow up genomic screening of CPHD patient cohort that were previously tested for changes in a coding sequences of genes with the use of the whole exome. We aimed to find contribution of rare copy number variations (CNVs). As a result, we identified genomic imbalances in 7 regions among 12 CPHD patients. Five out of seven regions showed copy gains whereas two presented losses of genomic fragment. Three regions with detected gains encompassed known CPHD genes namely LHX4, HESX1, and OTX2. Among new CPHD loci, the most interesting seem to be the region covering SIX3 gene, that is abundantly expressed in developing brain, and together with HESX1 contributes to pituitary organogenesis as it was evidenced before in functional studies. In conclusion, with the use of broadened genomic approach we identified copy number imbalances for 12 CPHD patients. Although further functional studies are required in order to estimate its true impact on expression pattern during pituitary organogenesis and CPHD etiology.

Classification for treatment urgency for the microphthalmia/anophthalmia spectrum using clinical and biometrical characteristics

PURPOSE

Current clinical classifications do not distinguish between the severity of the MICrophthalmia/Anophthalmia (MICA) spectrum with regard to treatment urgency. We aim to provide parameters for distinguishing mild, moderate and severe MICA using clinical and biometrical characteristics.

METHODS

We performed a single-centre, cross-sectional analysis of prospective cohort of 58 MICA children from September 2013 to February 2018 seen at the Amsterdam University Medical Center, The Netherlands. All patients with a visible underdeveloped globe were included. We performed full ophthalmic evaluation including horizontal palpebral fissure length, axial length by ultrasound and/or MRI measurements, paediatric and genetic evaluation. Cases were subdivided based on clinical characteristics. Biometrical data were used to calculate the relative axial length (rAL) and the relative horizontal palpebral fissure length (rHPF) compared with the healthy contralateral eye for unilateral cases.

RESULTS

In previously untreated patients, a strong correlation exists between rAL and rHPF, distinguishing between severe, moderate and mild subjects using rAL of 0-45%, 45-75% and 75%-100%, respectively. Clinical subgroups were randomly dispersed throughout the scatterplot.

CONCLUSION

Current classifications lack clinical implications for MICA patients. We suggest measuring eyelid length and axial length to classify the severity and determine treatment strategy. The 'severe' group has obvious asymmetry and abnormal socket configuration for which therapy should quickly be initiated; the 'moderately' affected group has normal socket anatomy with a microphthalmic eye with disturbing asymmetry for which treatment should be initiated within months of development; the 'mild' group has a slightly smaller axial length or less obvious eyelid asymmetry for which reconstructive correction is possible, but expansive conformer treatment is unnecessary.

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.

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.

Anophthalmia including next-generation sequencing-based approaches

Name of the disease (synonyms) See Table 1, Column 1-"Name of disease" and Column 2-"Alternative names". OMIM# of the disease See Table 1, Column 3-"OMIM# of the disease". Name of the analysed genes or DNA/chromosome segments and OMIM# of the gene(s) Core genes (irrespective of being tested by Sanger sequencing or next-generation sequencing): See Table 1, Column 4-"Cytogenetic location", Column 5-"Associated gene(s)" and Column 6-"OMIM# of associated gene(s)". Additional genes (if tested by next-generation sequencing, including Whole exome/genome sequencing and panel sequencing): See Table 2, Column 1-"Gene", Column 2-"Alternative names", Column 3-"OMIM# of gene" and Column 4-"Cytogenetic location". Review of the analytical and clinical validity as well as of the clinical utility of DNA-based testing for mutations in the gene(s) in diagnostic, predictive and prenatal settings, and for risk assessment in relatives.

Adrenal insufficiency: Physiology, clinical presentation and diagnostic challenges

Adrenal insufficiency (AI) is a serious condition, which can arise from pathology affecting the adrenal gland itself (primary adrenal insufficiency, PAI), hypothalamic or pituitary pathology (secondary adrenal insufficiency, SAI), or as a result of suppression of the hypothalamic-pituitaryadrenal (HPA) axis by exogenous glucocorticoid therapy (tertiary adrenal insufficiency, TAI). AI is associated with an increase in morbidity and mortality and a reduction in quality of life. In addition, the most common cause of PAI, autoimmune adrenalitis, may be associated with a variety of other autoimmune disorders. Untreated AI can present with chronic fatigue, weight loss and vulnerability to infection. The inability to cope with acute illness or infection can precipitate life-threatening adrenal crisis. It is therefore a critical diagnosis to make in a timely fashion, in order to institute appropriate management, aimed at reversing chronic ill health, preventing acute crises, and restoring quality of life. In this review, we will describe the normal physiology of the HPA axis and explain how knowledge of the physiology of this axis helps us understand the clinical presentation of AI, and forms the basis for the biochemical investigations which lead to the diagnosis of AI.

Genetics of syndromic ocular coloboma: CHARGE and COACH syndromes

Optic fissure closure defects result in uveal coloboma, a potentially blinding condition affecting between 0.5 and 2.6 per 10,000 births that may cause up to 10% of childhood blindness. Uveal coloboma is on a phenotypic continuum with microphthalmia (small eye) and anophthalmia (primordial/no ocular tissue), the so-called MAC spectrum. This review gives a brief overview of the developmental biology behind coloboma and its clinical presentation/spectrum. Special attention will be given to two prominent, syndromic forms of coloboma, namely, CHARGE (Coloboma, Heart defect, Atresia choanae, Retarded growth and development, Genital hypoplasia, and Ear anomalies/deafness) and COACH (Cerebellar vermis hypoplasia, Oligophrenia, Ataxia, Coloboma, and Hepatic fibrosis) syndromes. Approaches employed to identify genes involved in optic fissure closure in animal models and recent advances in live imaging of zebrafish eye development are also discussed.

A new imaging entity consistent with partial ectopic posterior pituitary gland: report of six cases

BACKGROUND

Abnormal posterior pituitary development including ectopic location has been associated with endocrine manifestations of anterior pituitary dysfunction.

OBJECTIVE

We describe an unreported clinical and radiologic entity we call partial ectopic posterior pituitary for which associated endocrine consequences are not known.

MATERIALS AND METHODS

We selected pediatric head MRI examinations from 2005 to 2017 based on the finding of a double midline sellar and suprasellar bright spot on T1-weighted sequence. Medical history, physical examination, pituitary hormonal profile and bone age evaluation were extracted from the medical record of the selected patients. An experienced pediatric neuroradiologist reviewed head MRIs, which were performed on 3-tesla (T) magnet and included at least sagittal T1-weighted imaging centered on the sella turcica obtained with and without fat suppression.

RESULTS

In six cases, two midline bright spots were identified on T1-weighted sequences obtained both with and without fat suppression. While one spot was located at the expected site of the neurohypophysis in the posterior sella, the second one was in the region of the median eminence, suggesting partial ectopic posterior pituitary gland. Growth hormone deficiency, either isolated (n=1) or combined with thyroid stimulating hormone deficiency (n=1) was found. None of the children had clinical signs of posterior pituitary dysfunction.

CONCLUSION

We describe an unreported imaging entity suggesting partial ectopic posterior pituitary gland in six children. Anterior pituitary hormone deficiencies might be detected in those children and long-term follow-up could provide additional information on the development of other pituitary hormone deficiencies.

The Molecular Basis of Human Anophthalmia and Microphthalmia

Human eye development is coordinated through an extensive network of genetic signalling pathways. Disruption of key regulatory genes in the early stages of eye development can result in aborted eye formation, resulting in an absent eye (anophthalmia) or a small underdeveloped eye (microphthalmia) phenotype. Anophthalmia and microphthalmia (AM) are part of the same clinical spectrum and have high genetic heterogeneity, with >90 identified associated genes. By understanding the roles of these genes in development, including their temporal expression, the phenotypic variation associated with AM can be better understood, improving diagnosis and management. This review describes the genetic and structural basis of eye development, focusing on the function of key genes known to be associated with AM. In addition, we highlight some promising avenues of research involving multiomic approaches and disease modelling with induced pluripotent stem cell (iPSC) technology, which will aid in developing novel therapies.

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.

Genetics of anophthalmia and microphthalmia. Part 2: Syndromes associated with anophthalmia-microphthalmia

As new genes for A/M are identified in the genomic era, the number of syndromes associated with A/M has greatly expanded. In this review, we provide a brief synopsis of the clinical presentation and molecular genetic etiology of previously characterized pathways involved in A/M, including the Sex-determining region Y-box 2 (SOX2), Orthodenticle Homeobox 2 (OTX2) and Paired box protein-6 (PAX6) genes, and the Stimulated by retinoic acid gene 6 homolog (STRA6), Aldehyde Dehydrogenase 1 Family Member A3 (ALDH1A3), and RA Receptor Beta (RARβ) genes that are involved in retinoic acid synthesis. Less common genetic causes of A/M, including genes involved in BMP signaling [Bone Morphogenetic Protein 4 (BMP4), Bone Morphogenetic Protein 7 (BMP7) and SPARC-related modular calcium-binding protein 1 (SMOC1)], genes involved in the mitochondrial respiratory chain complex [Holocytochrome c-type synthase (HCCS), Cytochrome C Oxidase Subunit 7B (COX7B), and NADH:Ubiquinone Oxidoreductase subunit B11 (NDUFB11)], the BCL-6 corepressor gene (BCOR), Yes-Associated Protein 1 (YAP1) and Transcription Factor AP-2 Alpha (TFAP2α), are more briefly discussed. We also review several recently described genes and pathways associated with A/M, including Smoothened (SMO) that is involved in Sonic hedgehog (SHH) signaling, Structural maintenance of chromosomes flexible hinge domain containing 1 (SMCHD1) and Solute carrier family 25 member 24 (SLC25A24), emphasizing phenotype-genotype correlations and shared pathways where relevant.

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.

Next generation sequencing panel based on single molecule molecular inversion probes for detecting genetic variants in children with hypopituitarism

BACKGROUND

Congenital Hypopituitarism is caused by genetic and environmental factors. Over 30 genes have been implicated in isolated and/or combined pituitary hormone deficiency. The etiology remains unknown for up to 80% of the patients, but most cases have been analyzed by limited candidate gene screening. Mutations in the PROP1 gene are the most common known cause, and the frequency of mutations in this gene varies greatly by ethnicity. We designed a custom array to assess the frequency of mutations in known hypopituitarism genes and new candidates, using single molecule molecular inversion probes sequencing (smMIPS).

METHODS

We used this panel for the first systematic screening for causes of hypopituitarism in children. Molecular inversion probes were designed to capture 693 coding exons of 30 known genes and 37 candidate genes. We captured genomic DNA from 51 pediatric patients with CPHD (n = 43) or isolated GH deficiency (IGHD) (n = 8) and their parents and conducted next generation sequencing.

RESULTS

We obtained deep coverage over targeted regions and demonstrated accurate variant detection by comparison to whole-genome sequencing in a control individual. We found a dominant mutation GH1, p.R209H, in a three-generation pedigree with IGHD.

CONCLUSIONS

smMIPS is an efficient and inexpensive method to detect mutations in patients with hypopituitarism, drastically limiting the need for screening individual genes by Sanger sequencing.

Prescreening whole exome sequencing results from patients with retinal degeneration for variants in genes associated with retinal degeneration

Background

Accurate clinical diagnosis and prognosis of retinal degeneration can be aided by the identification of the disease-causing genetic variant. It can confirm the clinical diagnosis as well as inform the clinician of the risk for potential involvement of other organs such as kidneys. It also aids in genetic counseling for affected individuals who want to have a child. Finally, knowledge of disease-causing variants informs laboratory investigators involved in translational research. With the advent of next-generation sequencing, identifying pathogenic mutations is becoming easier, especially the identification of novel pathogenic variants.

Methods

We used whole exome sequencing on a cohort of 69 patients with various forms of retinal degeneration and in whom screens for previously identified disease-causing variants had been inconclusive. All potential pathogenic variants were verified by Sanger sequencing and, when possible, segregation analysis of immediate relatives. Potential variants were identified by using a semi-masked approach in which rare variants in candidate genes were identified without knowledge of the clinical diagnosis (beyond "retinal degeneration") or inheritance pattern. After the initial list of genes was prioritized, genetic diagnosis and inheritance pattern were taken into account.

Results

We identified the likely pathogenic variants in 64% of the subjects. Seven percent had a single heterozygous mutation identified that would cause recessive disease and 13% had no obviously pathogenic variants and no family members available to perform segregation analysis. Eleven subjects are good candidates for novel gene discovery. Two de novo mutations were identified that resulted in dominant retinal degeneration.

Conclusion

Whole exome sequencing allows for thorough genetic analysis of candidate genes as well as novel gene discovery. It allows for an unbiased analysis of genetic variants to reduce the chance that the pathogenic mutation will be missed due to incomplete or inaccurate family history or analysis at the early stage of a syndromic form of retinal degeneration.

Clinical characteristics of septo-optic dysplasia accompanied by congenital central hypothyroidism in Japan

Septo-optic dysplasia (SOD) is a congenital anomaly in which agenesis of the septum pellucidum and optic nerve hypoplasia are accompanied by hypopituitarism. Typically, the symptoms develop in 3 organs, the brain, eyes, and pituitary, and approximately one third of the patients present with all of the three cardinal features. The diagnostic criteria for SOD were established in Japan in 2015. The purpose of this study is to review clinical features regarding SOD patients with hypopituitarism in Japan. In this study, 21 patients with SOD were identified by a questionnaire survey for congenital central hypothyroidism. All 3 symptoms of SOD, agenesis of the septum pellucidum, optic nerve hypoplasia, and endocrine abnormalities, were noted in 8 of the 21 patients. Various combinations of pituitary hormone deficiencies were observed in patients with SOD, although SOD is a rare, heterogeneous, and phenotypically variable disorder, some patients develop hypoglycemia and convulsions after birth, and early intervention with hormone replacement is necessary in severe cases. In addition, 14 cases were complicated by both developmental delay and epilepsy, and 16 cases involved eye abnormalities. Therefore, in addition to an early endocrinological diagnosis and hormone replacement, consultation with both pediatric neurologists and pediatric ophthalmologists is necessary.

Hypothalamic sonic hedgehog is required for cell specification and proliferation of LHX3/LHX4 pituitary embryonic precursors

Sonic hedgehog (SHH) is an essential morphogenetic signal that dictates cell fate decisions in several developing organs in mammals. In vitro data suggest that SHH is required to specify LHX3⁺/LHX4⁺ Rathke's pouch (RP) progenitor identity. However, in vivo studies have failed to reveal such a function, supporting instead a crucial role for SHH in promoting proliferation of these RP progenitors and for differentiation of pituitary cell types. Here, we have used a genetic approach to demonstrate that activation of the SHH pathway is necessary to induce LHX3⁺/LHX4⁺ RP identity in mouse embryos. First, we show that conditional deletion of Shh in the anterior hypothalamus results in a fully penetrant phenotype characterised by a complete arrest of RP development, with lack of Lhx3/Lhx4 expression in RP epithelium at 9.0 days post coitum (dpc) and total loss of pituitary tissue by 12.5 dpc. Conversely, overactivation of the SHH pathway by conditional deletion of Ptch1 in RP progenitors leads to severe hyperplasia and enlargement of the Sox2⁺ stem cell compartment by the end of gestation.

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.

Recent advances in central congenital hypothyroidism

Central congenital hypothyroidism (CCH) may occur in isolation, or more frequently in combination with additional pituitary hormone deficits with or without associated extrapituitary abnormalities. Although uncommon, it may be more prevalent than previously thought, affecting up to 1:16 000 neonates in the Netherlands. Since TSH is not elevated, CCH will evade diagnosis in primary, TSH-based, CH screening programs and delayed detection may result in neurodevelopmental delay due to untreated neonatal hypothyroidism. Alternatively, coexisting growth hormones or ACTH deficiency may pose additional risks, such as life threatening hypoglycaemia. Genetic ascertainment is possible in a minority of cases and reveals mutations in genes controlling the TSH biosynthetic pathway (TSHB, TRHR, IGSF1) in isolated TSH deficiency, or early (HESX1, LHX3, LHX4, SOX3, OTX2) or late (PROP1, POU1F1) pituitary transcription factors in combined hormone deficits. Since TSH cannot be used as an indicator of euthyroidism, adequacy of treatment can be difficult to monitor due to a paucity of alternative biomarkers. This review will summarize the normal physiology of pituitary development and the hypothalamic-pituitary-thyroid axis, then describe known genetic causes of isolated central hypothyroidism and combined pituitary hormone deficits associated with TSH deficiency. Difficulties in diagnosis and management of these conditions will then be discussed.

Relationship between pituitary stalk (PS) visibility and the severity of hormone deficiencies: PS interruption syndrome revisited

CONTEXT

Pituitary stalk interruption syndrome (PSIS) is a rare cause of combined pituitary hormone deficiency characterized by a triad shown in pituitary imaging, yet it has never been evaluated due to the visibility of pituitary stalk (PS) in imaging findings.

OBJECTIVE

The major objective of the study was to systematically describe the disease including clinical presentations, imaging findings and to estimate the severity of anterior pituitary hormone deficiency based on the visibility of the PS.

METHODS

This was a retrospective study including 74 adult patients with PSIS in Shanghai Clinical Center for Endocrine and Metabolic Diseases between January 2010 and June 2014. Sixty had invisible PS according to the findings on MRI, while the rest had a thin or intersected PS. Basic characteristics and hormonal status were compared.

RESULTS

Of the 74 patients with PSIS, age at diagnosis was 25 (22-28) years. Absent pubertal development (97·3%) was the most common presenting symptom, followed by short stature. Insulin tolerance test (ITT) and gonadotrophin-releasing hormone (GnRH) stimulation test were used to evaluate the function of anterior pituitary. The prevalence of isolated deficiency in growth hormone (GH), gonadotrophins, corticotrophin and thyrotrophin were 100%, 97·2%, 88·2% and 70·3%, respectively. Although the ratio of each deficiency did not vary between patients with invisible PS and with visible PS, panhypopituitarism occurred significantly more frequent in patients with invisible PS. Patients with invisible PS had significantly lower levels of luteinizing hormone (LH), follicle stimulation hormone (FSH) and hormones from targeted glands including morning cortisol, 24-h urine free cortisol, free triiodothyronine (FT3), free thyroxine (FT4) and testosterone (T) in male than patients with visible PS. Moreover, patients with invisible PS had lower peak LH and FSH in GnRH stimulation test, and higher peak cortisol in ITT while peak GH remained unchanged between two groups.

CONCLUSIONS

The prevalence of multiple anterior pituitary hormone deficiency was high in adult patients with PSIS. And more importantly, we found the visibility of PS shown on MRI might be an indication of the severity of PSIS.

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.

Deletion of OTX2 in neural ectoderm delays anterior pituitary development

OTX2 is a homeodomain transcription factor that is necessary for normal head development in mouse and man. Heterozygosity for loss-of-function alleles causes an incompletely penetrant, haploinsufficiency disorder. Affected individuals exhibit a spectrum of features that range from developmental defects in eye and/or pituitary development to acephaly. To investigate the mechanism underlying the pituitary defects, we used different cre lines to inactivate Otx2 in early head development and in the prospective anterior and posterior lobes. Mice homozygous for Otx2 deficiency in early head development and pituitary oral ectoderm exhibit craniofacial defects and pituitary gland dysmorphology, but normal pituitary cell specification. The morphological defects mimic those observed in humans and mice with OTX2 heterozygous mutations. Mice homozygous for Otx2 deficiency in the pituitary neural ectoderm exhibited altered patterning of gene expression and ablation of FGF signaling. The posterior pituitary lobe and stalk, which normally arise from neural ectoderm, were extremely hypoplastic. Otx2 expression was intact in Rathke's pouch, the precursor to the anterior lobe, but the anterior lobe was hypoplastic. The lack of FGF signaling from the neural ectoderm was sufficient to impair anterior lobe growth, but not the differentiation of hormone-producing cells. This study demonstrates that Otx2 expression in the neural ectoderm is important intrinsically for the development of the posterior lobe and pituitary stalk, and it has significant extrinsic effects on anterior pituitary growth. Otx2 expression early in head development is important for establishing normal craniofacial features including development of the brain, eyes and pituitary gland.

Midbrain-hindbrain involvement in septo-optic dysplasia

BACKGROUND AND PURPOSE

Midbrain-hindbrain involvement in septo-optic dysplasia has not been well described, despite reported mutations of genes regulating brain stem patterning. We aimed to describe midbrain-hindbrain involvement in patients with septo-optic dysplasia and to identify possible clinical-neuroimaging correlations.

MATERIALS AND METHODS

Using MR imaging, we categorized 38 patients (21 males) based on the presence (group A, 21 patients) or absence (group B, 17 patients) of visible brain stem anomalies. We measured height and anteroposterior diameter of midbrain, pons, and medulla, anteroposterior midbrain/pons diameter (M/P ratio), vermian height, and tegmento-vermian angle, and compared the results with 114 healthy age-matched controls. Furthermore, patients were subdivided based on the type of midline anomalies. The associations between clinical and neuroradiological features were investigated. Post hoc tests were corrected according to Bonferroni adjustment (pB).

RESULTS

Patients with brain stem abnormalities had smaller anteroposterior pons diameter than controls (pB < .0001) and group B (pB = .012), higher M/P ratio than controls (pB < .0001) and group B (pB < .0001), and smaller anteroposterior medulla diameter (pB = .001), pontine height (pB = .00072), and vermian height (pB = .0009) than controls. Six of 21 patients in group A had thickened quadrigeminal plate, aqueductal stenosis, and hydrocephalus; 3 also had agenesis of the epithalamus. One patient had a short midbrain with long pons and large superior vermis. There was a statistically significant association between brain stem abnormalities and callosal dysgenesis (P = .011) and developmental delay (P = .035), respectively.

CONCLUSION

Midbrain-hindbrain abnormalities are a significant, albeit underrecognized, component of the septo-optic dysplasia spectrum, and are significantly associated with developmental delay in affected patients.

The role of homeobox genes in retinal development and disease

Homeobox genes are an evolutionarily conserved class of transcription factors that are critical for development of many organ systems, including the brain and eye. During retinogenesis, homeodomain-containing transcription factors, which are encoded by homeobox genes, play essential roles in the regionalization and patterning of the optic neuroepithelium, specification of retinal progenitors and differentiation of all seven of the retinal cell classes that derive from a common progenitor. Homeodomain transcription factors control retinal cell fate by regulating the expression of target genes required for retinal progenitor cell fate decisions and for terminal differentiation of specific retinal cell types. The essential role of homeobox genes during retinal development is demonstrated by the number of human eye diseases, including colobomas and anophthalmia, which are attributed to homeobox gene mutations. In the following review, we highlight the role of homeodomain transcription factors during retinogenesis and regulation of their gene targets. Understanding the complexities of vertebrate retina development will enhance our ability to drive differentiation of specific retinal cell types towards novel cell-based replacement therapies for retinal degenerative diseases.

Pituitary stalk interruption syndrome in 58 Chinese patients: clinical features and genetic analysis

OBJECTIVES

Pituitary stalk interruption syndrome (PSIS) is rare and its clinical features and pathogenesis are poorly understood. This study characterized the clinical and genetic features of PSIS in Chinese patients.

DESIGN AND PATIENTS

Clinical data of 58 patients with PSIS and 46 patients with GH deficiency but a normal pituitary stalk (NPS) were retrospectively analysed. HESX1, LHX4, OTX2 and SOX3 polymorphisms were screened in 33 PSIS patients, and GH1 and GHRHR in 4 NPS patients.

RESULTS

Deficiency of GH was 100% in both PSIS and NPS groups. Other deficiency rates for PSIS and NPS groups were as follows: ACTH, 77·6% and 23·9%; TSH, 43·1% and 10·9%; LH/FSH, 94·2% and 47·4%; and combined pituitary hormone, 93·1% and 41·3% respectively. In PSIS and NPS patients, the percentages of anterior pituitary hypoplasia were 98·3% and 54·3%, pituitary stalk abnormality were 100% and 0%, and ectopic neurohypophysis were 91·4% and 0%. A novel heterozygous sequence variant (c.142A>T, p.T48S) was found in HESX1 in one PSIS patient, 3 polymorphisms (c.63T>C, p.G21G; c.450C>T, p.N150N; and c.983A>G, p.N328S) in LHX4 in 7, 1 and 31 PSIS patients, respectively, and a hemizygous polymorphism (c.157G>C, p.V53L) in SOX3 in one PSIS patient. No OTX2 abnormality was detected in PSIS patients, and no GH1 or GHRHR polymorphisms in NPS patients.

CONCLUSIONS

Compared with NPS, PSIS patients had more severe anterior pituitary hormone deficiency, lower anterior pituitary hormone secretion and higher probability of abnormal pituitary morphology. HESX1, LHX4 and SOX3 polymorphisms may be associated with PSIS.

Molecular and Clinical Findings in Patients with LHX4 and OTX2 Mutations

The pituitary gland produces hormones that play important roles in both the development and homeostasis of the body. Ontogeny of the anterior and posterior pituitary is orchestrated by inputs from neighboring tissues, cellular signaling molecules and transcription factors. Disruption of expression or function of these factors has been implicated in the etiology of combined pituitary hormone deficiency (CPHD). These include the transcription factors HESX1, PROP1, POU1F1, LHX3, LHX4, OTX2, SOX2, SOX3 and GLI2. This review focuses on summarizing most recent mutations in LHX4 and OTX2 responsible for pituitary hormone deficiency. In both genetic defects of LHX4 and OTX2, there is high variability in clinical manifestations even in the same family. In addition, there is no clear phenotype-genotype correlation. These findings indicate that the other genetic and/or environmental factors influence the phenotype. In addition, the variability might reflect a plasticity during pituitary development and maintenance. Over the past two decades, a genetic basis for pituitary hormone deficiency and the mechanism of pituitary development have been clarified. It should be kept in mind that this review is not comprehensive, and defects of other transcriptional factors have been described in patients with CPHD. Furthermore, the causes in many patients with CPHD have not yet been determined. Therefore, continuing efforts for the clarification of the etiology are necessary.

Molecular and Clinical Findings in Patients with LHX4 and OTX2 Mutations

The pituitary gland produces hormones that play important roles in both the development and homeostasis of the body. Ontogeny of the anterior and posterior pituitary is orchestrated by inputs from neighboring tissues, cellular signaling molecules and transcription factors. Disruption of expression or function of these factors has been implicated in the etiology of combined pituitary hormone deficiency (CPHD). These include the transcription factors HESX1, PROP1, POU1F1, LHX3, LHX4, OTX2, SOX2, SOX3 and GLI2. This review focuses on summarizing most recent mutations in LHX4 and OTX2 responsible for pituitary hormone deficiency. In both genetic defects of LHX4 and OTX2, there is high variability in clinical manifestations even in the same family. In addition, there is no clear phenotype-genotype correlation. These findings indicate that the other genetic and/or environmental factors influence the phenotype. In addition, the variability might reflect a plasticity during pituitary development and maintenance. Over the past two decades, a genetic basis for pituitary hormone deficiency and the mechanism of pituitary development have been clarified. It should be kept in mind that this review is not comprehensive, and defects of other transcriptional factors have been described in patients with CPHD. Furthermore, the causes in many patients with CPHD have not yet been determined. Therefore, continuing efforts for the clarification of the etiology are necessary.

Clinical and mutation analysis of 51 probands with anophthalmia and/or severe microphthalmia from a single center

Clinical evaluation and mutation analysis was performed in 51 consecutive probands with severe eye malformations - anophthalmia and/or severe microphthalmia - seen in a single specialist ophthalmology center. The mutation analysis consisted of bidirectional sequencing of the coding regions of SOX2, OTX2, PAX6 (paired domain), STRA6, BMP4, SMOC1, FOXE3, and RAX, and genome-wide array-based copy number assessment. Fifteen (29.4%) of the 51 probands had likely causative mutations affecting SOX2 (9/51), OTX2 (5/51), and STRA6 (1/51). Of the cases with bilateral anophthalmia, 9/12 (75%) were found to be mutation positive. Three of these mutations were large genomic deletions encompassing SOX2 (one case) or OTX2 (two cases). Familial inheritance of three intragenic, plausibly pathogenic, and heterozygous mutations was observed. An unaffected carrier parent of an affected child with an identified OTX2 mutation confirmed the previously reported nonpenetrance for this disorder. Two families with SOX2 mutations demonstrated a parent and child both with significant but highly variable eye malformations. Heterozygous loss-of-function mutations in SOX2 and OTX2 are the most common genetic pathology associated with severe eye malformations and bi-allelic loss-of-function in STRA6 is confirmed as an emerging cause of nonsyndromal eye malformations.

Identification and analysis of two novel sites of rat GnRH receptor gene promoter activity: the pineal gland and retina

BACKGROUND AND AIMS

In mammals, activation of pituitary GnRH receptor (GnRHR) by hypothalamic GnRH increases the synthesis and secretion of LH and FSH, which, in turn, regulate gonadal functions. However, GnRHR gene (Gnrhr) expression is not restricted to the pituitary.

METHODS

To gain insight into the extrapituitary expression of Gnrhr, a transgenic mouse model that expresses the human placental alkaline phosphatase reporter gene driven by the rat Gnrhr promoter was created.

RESULTS

This study shows that the rat Gnrhr promoter is operative in two functionally related organs, the pineal gland, as early as embryonic day (E) 13.5, and the retina where activity was only detected at E17.5. Accordingly, Gnrhr mRNA were present in both tissues. Transcription factors known to regulate Gnrhr promoter activity such as the LIM homeodomain factors LHX3 and ISL1 were also detected in the retina. Furthermore, transient transfection studies in CHO and gonadotrope cells revealed that OTX2, a major transcription factor in both pineal and retina cell differentiation, is able to activate the Gnrhr promoter together with either CREB or PROP1, depending on the cell context.

CONCLUSION

Rather than using alternate promoters, Gnrhr expression is directed to diverse cell lineages through specific associations of transcription factors acting on distinct response elements along the same promoter. These data open new avenues regarding GnRH-mediated control of seasonal and circadian rhythms in reproductive physiology.

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.

A novel OTX2 mutation in a patient with combined pituitary hormone deficiency, pituitary malformation, and an underdeveloped left optic nerve

Orthodenticle homolog 2 (OTX2) is a homeobox family transcription factor required for brain and eye formation. Various genetic alterations in OTX2 have been described, mostly in patients with severe ocular malformations. In order to expand the knowledge of the spectrum of OTX2 mutation, we performed OTX2 mutation screening in 92 patients with combined pituitary hormone deficiency (CPHD). We directly sequenced the coding regions and exon-intron boundaries of OTX2 in 92 CPHD patients from the Dutch HYPOPIT study in whom mutations in the classical CPHD genes PROP1, POU1F1, HESX1, LHX3, and LHX4 had been ruled out. Among 92 CPHD patients, we identified a novel heterozygous missense mutation c.401C>G (p.Pro134Arg) in a patient with CPHD, pituitary malformation, and an underdeveloped left optic nerve. Binding of both the wild-type and mutant OTX2 proteins to bicoid binding sites was equivalent; however, the mutant OTX2 exhibited decreased transactivation. We describe a novel missense heterozygous OTX2 mutation that acts as a dominant negative inhibitor of target gene expression in a patient with CPHD, pituitary malformation, and optic nerve hypoplasia. We provide an overview of all OTX2 mutations described till date, which show that OTX2 is a promising candidate gene for genetic screening of patients with CPHD or isolated GH deficiency (IGHD). As the majority of the OTX2 mutations found in patients with CPHD, IGHD, or short stature have been found in exon 5, we recommend starting mutational screening in those patients in exon 5 of the gene.

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.

Genetic disorders of the pituitary

PURPOSE OF REVIEW

To discuss pituitary development and function related to those factors in which molecular defects resulting in combined pituitary hormone deficiency have been described in humans, and to describe recently reported novel mutations in these factors (January 2010 to September 2011).

RECENT FINDINGS

Novel mutations have been found in transcription factors involved in pituitary development, HESX1; LHX3; LHX4; SOX3; Prophet of Pit-1; and POU1FI, and in some of the signaling molecules expressed in the ventral diencephalon (fibroblast growth factor 8 and GLI2). There is phenotypic variability for the same mutation suggesting variable penetrance due to other genetic, epigenetic, or environmental factors. The incidence of mutations in these factors is low suggesting that other genes or environmental factors are responsible for the majority of cases of combined pituitary hormone deficiency.

SUMMARY

Development of the pituitary gland and pituitary cell determination and specification depend on the expression and interaction of signaling molecules and transcription factors in overlapping, but distinct, spatial and temporal patterns. Studying genotype-phenotype correlations in patients with mutations in these factors give insight into the mechanisms involved in normal pituitary development and function.

Phenotype-genotype correlations in congenital isolated growth hormone deficiency (IGHD)

Isolated growth hormone deficiency (IGHD) may be congenital, often due to genetic mutations, or acquired as a result of other factors such as cranial irradiation. The commonest genes implicated in its genetic etiology are those encoding growth hormone (GH1) and the receptor for GH-releasing hormone (GHRHR). Rarely, IGHD may be caused by mutations in transcription factors (HESX1, SOX3, OTX2) or be the first presentation before the development of other pituitary hormone deficiencies. IGHD has been classified in four genetic forms (type IA, IB, II and III). Despite the increasing number of genes implicated in the etiology of IGHD, mutations in known genes account only for a small percentage of cases; therefore, other as yet unidentified factors may be implicated in its etiology. Although there is no strict genotype/phenotype correlation in patients with IGHD, there are some emerging patterns that may guide us towards a genetic diagnosis of the condition. There is increasing understanding that the phenotype of patients with IGHD is highly variable and sometimes even evolving, dictating the need for long term follow-up in these cases.

Eye development genes and known syndromes

Anophthalmia and microphthalmia (A/M) are significant eye defects because they can have profound effects on visual acuity. A/M is associated with non-ocular abnormalities in an estimated 33-95% of cases and around 25% of patients have an underlying genetic syndrome that is diagnosable. Syndrome recognition is important for targeted molecular genetic testing, prognosis and for counseling regarding recurrence risks. This review provides clinical and molecular information for several of the commonest syndromes associated with A/M: Anophthalmia-Esophageal-Genital syndrome, caused by SOX2 mutations, Anophthalmia and pituitary abnormalities caused by OTX2 mutations, Matthew-Wood syndrome caused by STRA6 mutations, oculofaciocardiodental syndrome and Lenz microphthalmia caused by BCOR mutations, Microphthalmia Linear Skin pigmentation syndrome caused by HCCS mutations, Anophthalmia, pituitary abnormalities, polysyndactyly caused by BMP4 mutations and Waardenburg anophthalmia caused by mutations in SMOC1. In addition, we briefly discuss the ocular and extraocular phenotypes associated with several other important eye developmental genes, including GDF6, VSX2, RAX, SHH, SIX6 and PAX6.