Role of GLI2 in hypopituitarism phenotype

Genetic diagnosis of congenital hypopituitarism in Turkish patients by a target gene panel: novel pathogenic variants in GHRHR, GLI2, LHX4 and POU1F1 genes

Objective

Congenital hypopituitarism (CH) is a rare disease characterized by one or more hormone deficiencies of the pituitary gland. To date, many genes have been associated with CH. In this study, we identified the allelic variant spectrum of 11 causative genes in Turkish patients with CH.

Materials and methods

This study included 47 patients [21 girls (44.6%) and 26 boys (55.4%)] from 45 families. To identify the genetic etiology, we screened 11 candidate genes associated with CH using next-generation sequencing. To confirm and detect the status of the specific familial variant in relatives, Sanger sequencing was also performed.

Results

We identified 12 possible pathogenic variants in GHRHR, GH1, GLI2, PROP-1, POU1F1, and LHX4 in 11 patients (23.4%), of which six were novel variants: two in GHRHR, two in POU1F1, one in GLI2, and one in LHX4. In all patients, these variants were most frequently found in GLI2, followed by PROP-1 and GHRHR.

Conclusion

Genetic causes were determined in only 23.4% of all patients with CH and 63% of molecularly diagnosed patients (7/11) from consanguineous families. Despite advances in genetics, we were unable to identify the genetic etiology of most patients with CH, suggesting the effect of unknown genes or environmental factors. More genetic studies are necessary to understand the etiology of CH.

Pituitary Stem Cell Regulation by Zeb2 and BMP Signaling

Epithelial to mesenchymal transition (EMT) is important for many developing organs, and for wound healing, fibrosis, and cancer. Pituitary stem cells undergo an EMT-like process as they migrate and initiate differentiation, but little is known about the input of signaling pathways or the genetic hierarchy of the transcriptional cascade. Prop1 mutant stem cells fail to undergo changes in cellular morphology, migration, and transition to the Pou1f1 lineage. We used Prop1 mutant mice to identify the changes in gene expression that are affiliated with EMT-like processes. BMP and TGF-β family gene expression was reduced in Prop1 mutants and Elf5, a transcription factor that characteristically suppresses EMT, had elevated expression. Genes involved in cell-cell contact such as cadherins and claudins were elevated in Prop1 mutants. To establish the genetic hierarchy of control, we manipulated gene expression in pituitary stem cell colonies. We determined that the EMT inducer, Zeb2, is necessary for robust BMP signaling and repression of Elf5. We demonstrated that inhibition of BMP signaling affects expression of target genes in the Id family, but it does not affect expression of other EMT genes. Zeb2 is necessary for expression of the SHH effector gene Gli2. However, knock down of Gli2 has little effect on the EMT-related genes, suggesting that it acts through a separate pathway. Thus, we have established the genetic hierarchy involved in the transition of pituitary stem cells to differentiation.

Case report: A case of Culler-Jones syndrome caused by a novel mutation of GLI2 gene and literature review

Culler-Jones syndrome is a rare clinical phenomenon with diverse manifestations and is prone to misdiagnosis. We report one patient who presented with a 10-year history of anosmia and a 1-year history of epididymal pain. Kallmann syndrome was suspected initially. The results of his laboratory tests, imaging, and genetic testing, however, combined to provide a conclusive diagnosis of Culler-Jones syndrome. With the aid of high-throughput sequencing technology, the GLI2 gene c.527A>G (p.Tyr176Cys) heterozygous mutation in the child was identified. No published works have yet described this mutation site. We described Culler-Jones syndrome in a child at length. We recommend that Culler-Jones syndrome be taken into account when considering the spectrum of disorders associated with abnormal growth and development in children. Once diagnosed, individualized hormone replacement treatment is required for each patient.

Presentation and diagnosis of childhood-onset combined pituitary hormone deficiency: A single center experience from over 30 years

BACKGROUND

Childhood-onset combined pituitary hormone deficiency (CPHD) has a wide spectrum of etiologies and genetic causes for congenital disease. We aimed to describe the clinical spectrum and genetic etiologies of CPHD in a single tertiary center and estimate the population-level incidence of congenital CPHD.

METHODS

The retrospective clinical cohort comprised 124 CPHD patients (48 with congenital CPHD) treated at the Helsinki University Hospital (HUH) Children's Hospital between 1985 and 2018. Clinical data were collected from the patient charts. Whole exome sequencing was performed in 21 patients with congenital CPHD of unknown etiology.

FINDINGS

The majority (61%;76/124) of the patients had acquired CPHD, most frequently due to craniopharyngiomas and gliomas. The estimated incidence of congenital CPHD was 1/16 000 (95%CI, 1/11 000-1/24 000). The clinical presentation of congenital CPHD in infancy included prolonged/severe neonatal hypoglycaemia, prolonged jaundice, and/or micropenis/bilateral cryptorchidism in 23 (66%) patients; despite these clinical cues, only 76% of them were referred to endocrine investigations during the first year of life. The median delay between the first violation of the growth screening rules and the initiation of GH Rx treatment among all congenital CPHD patients was 2·2 years, interquartile range 1·2-3·7 years. Seven patients harbored pathogenic variants in PROP1, SOX3, TBC1D32, OTX2, and SOX2, and one patient carried a likely pathogenic variant in SHH (c.676G>A, p.(Ala226Thr)).

INTERPRETATION

Our study suggests that congenital CPHD can occur in 1/16 000 children, and that patients frequently exhibit neonatal cues of hypopituitarism and early height growth deflection. These results need to be corroborated in future studies and might inform clinical practice.

FUNDING

Päivikki and Sakari Sohlberg Foundation, Biomedicum Helsinki Foundation, and Emil Aaltonen Foundation research grants.

Deleterious Rare Mutations of GLI1 Dysregulate Sonic Hedgehog Signaling in Human Congenital Heart Disease

The Glioma-associated oncogene (Gli) family members of zinc finger DNA-binding proteins are core effectors of Sonic hedgehog (SHH) signaling pathway. Studies in model organisms have identified that the Gli genes play critical roles during organ development, including the heart, brain, kidneys, etc. Deleterious mutations in GLI genes have previously been revealed in several human developmental disorders, but few in congenital heart disease (CHD). In this study, the mutations in GLI1-3 genes were captured by next generation sequencing in human cohorts composed of 412 individuals with CHD and 213 ethnically matched normal controls. A total of 20 patient-specific nonsynonymous rare mutations in coding regions of human GLI1-3 genes were identified. Functional analyses showed that GLI1 c.820G> T (p.G274C) is a gain-of-function mutation, while GLI1 c.878G>A (p.R293H) and c.1442T>A (p.L481X) are loss-of-function mutations. Our findings suggested that deleterious rare mutations in GLI1 gene broke the balance of the SHH signaling pathway regulation and may constitute a great contribution to human CHD, which shed new light on understanding genetic mechanism of embryo cardiogenesis regulated by SHH signaling.

Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism

Variants in transcription factor GLI2 have been associated with hypopituitarism and structural brain abnormalities, occasionally including holoprosencephaly (HPE). Substantial phenotypic variability and nonpenetrance have been described, posing difficulties in the counseling of affected families. We present three individuals with novel likely pathogenic GLI2 variants, two with truncating and one with a de novo missense variant p.(Ser548Leu), and review the literature for comprehensive phenotypic descriptions of individuals with confirmed pathogenic (a) intragenic GLI2 variants and (b) chromosome 2q14.2 deletions encompassing only GLI2. We show that most of the 31 missense variants previously reported as pathogenic are likely benign or, at most, low-risk variants. Four Zn-finger variants: p.(Arg479Gly), p.(Arg516Pro), p.(Gly518Lys), and p.(Tyr575His) were classified as likely pathogenic, and three other variants as possibly pathogenic: p.(Pro253Ser), p.(Ala593Val), and p.(Pro1243Leu). We analyze the phenotypic descriptions of 60 individuals with pathogenic GLI2 variants and evidence a morbidity spectrum that includes hypopituitarism (58%), HPE (6%) or other brain structure abnormalities (15%), orofacial clefting (17%) and dysmorphic facial features (35%). We establish that truncating and Zn-finger variants in GLI2 are associated with a high risk of hypopituitarism, and that a solitary median maxillary central incisor is part of the GLI2-related phenotypic variability. The most prevalent phenotypic feature is post-axial polydactyly (65%) which is also the mildest phenotypic expression of the condition, reported in many parents of individuals with systemic findings. Our approach clarifies clinical risks and the important messages to discuss in counseling for a pathogenic GLI2 variant.

Molecular Bases of Human Malformation Syndromes Involving the SHH Pathway: GLIA/R Balance and Cardinal Phenotypes

Human hereditary malformation syndromes are caused by mutations in the genes of the signal transduction molecules involved in fetal development. Among them, the Sonic hedgehog (SHH) signaling pathway is the most important, and many syndromes result from its disruption. In this review, we summarize the molecular mechanisms and role in embryonic morphogenesis of the SHH pathway, then classify the phenotype of each malformation syndrome associated with mutations of major molecules in the pathway. The output of the SHH pathway is shown as GLI activity, which is generated by SHH in a concentration-dependent manner, i.e., the sum of activating form of GLI (GLIA) and repressive form of GLI (GLIR). Which gene is mutated and whether the mutation is loss-of-function or gain-of-function determine in which concentration range of SHH the imbalance occurs. In human malformation syndromes, too much or too little GLI activity produces symmetric phenotypes affecting brain size, craniofacial (midface) dysmorphism, and orientation of polydactyly with respect to the axis of the limb. The symptoms of each syndrome can be explained by the GLIA/R balance model.

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.

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.

Pituitary stalk interruption syndrome

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

Chiari 1 malformation and exome sequencing in 51 trios: the emerging role of rare missense variants in chromatin-remodeling genes

Type 1 Chiari malformation (C1M) is characterized by cerebellar tonsillar herniation of 3–5 mm or more, the frequency of which is presumably much higher than one in 1000 births, as previously believed. Its etiology remains undefined, although a genetic basis is strongly supported by C1M presence in numerous genetic syndromes associated with different genes. Whole-exome sequencing (WES) in 51 between isolated and syndromic pediatric cases and their relatives was performed after confirmation of the defect by brain magnetic resonance image (MRI). Moreover, in all the cases showing an inherited candidate variant, brain MRI was performed in both parents and not only in the carrier one to investigate whether the defect segregated with the variant. More than half of the variants were Missense and belonged to the same chromatin-remodeling genes whose protein truncation variants are associated with severe neurodevelopmental syndromes. In the remaining cases, variants have been detected in genes with a role in cranial bone sutures, microcephaly, neural tube defects, and RASopathy. This study shows that the frequency of C1M is widely underestimated, in fact many of the variants, in particular those in the chromatin-remodeling genes, were inherited from a parent with C1M, either asymptomatic or with mild symptoms. In addition, C1M is a Mendelian trait, in most cases inherited as dominant. Finally, we demonstrate that modifications of the genes that regulate chromatin architecture can cause localized anatomical alterations, with symptoms of varying degrees.

A case series of a mother and two daughters with a GLI2 gene deletion demonstrating variable expressivity and incomplete penetrance

This case series and review of the literature support that patients with pathogenic variants of the GLI2 gene demonstrate an autosomal dominant inheritance pattern, variable expressivity, and incomplete penetrance.

Requirement of FAT and DCHS protocadherins during hypothalamic-pituitary development

Pituitary developmental defects lead to partial or complete hormone deficiency and significant health problems. The majority of cases are sporadic and of unknown cause. We screened 28 patients with pituitary stalk interruption syndrome (PSIS) for mutations in the FAT/DCHS family of protocadherins that have high functional redundancy. We identified seven variants, four of which putatively damaging, in FAT2 and DCHS2 in six patients with pituitary developmental defects recruited through a cohort of patients with mostly ectopic posterior pituitary gland and/or pituitary stalk interruption. All patients had growth hormone deficiency and two presented with multiple hormone deficiencies and small glands. FAT2 and DCHS2 were strongly expressed in the mesenchyme surrounding the normal developing human pituitary. We analyzed Dchs2-/- mouse mutants and identified anterior pituitary hypoplasia and partially penetrant infundibular defects. Overlapping infundibular abnormalities and distinct anterior pituitary morphogenesis defects were observed in Fat4-/- and Dchs1-/- mouse mutants but all animal models displayed normal commitment to the anterior pituitary cell type. Together our data implicate FAT/DCHS protocadherins in normal hypothalamic-pituitary development and identify FAT2 and DCHS2 as candidates underlying pituitary gland developmental defects such as ectopic pituitary gland and/or pituitary stalk interruption.

Ectopic Posterior Pituitary, Polydactyly, Midfacial Hypoplasia and Multiple Pituitary Hormone Deficiency due to a Novel Heterozygous IVS11-2A>C(c.1957-2A>C) Mutation in the GLI2 Gene

A novel heterozygous IVS11-2A>C(c.1957-2A>C) mutation in the GLI2 gene is reported. There was an extremely distinct phenotypical expression in two siblings and their father. The index case was a boy who developed cholestasis and hypoglycaemia in the neonatal period. He had bilateral postaxial polydactyly, mid-facial hypoplasia, high palatal arch, micropenis, and bilateral cryptorchidism. Laboratory examination revealed a diagnosis of multiple pituitary hormone deficiency. There was severe anterior pituitary hypoplasia, absent pituitary stalk and ectopic posterior pituitary on magnetic resonance imaging which suggested pituitary stalk interruption syndrome with no other midline structural abnormality. Molecular genetic analysis revealed a novel heterozygous splicing IVS11-2A>C(c.1957-2A>C) mutation detected in the GLI2 gene. His father and a six-year-old brother with the identical mutation also had unilateral postaxial polydactyly and mid-facial hypoplasia although there was no pituitary hormone deficiency. This novel heterozygous GLI2 mutation detected appears to present with an extremely variable clinical phenotype, even in related individuals with an identical mutation, suggesting incomplete penetrance of this GLI2 mutation.

Genetic Anomalies of Growth Hormone Deficiency in Pediatrics

Several different proteins regulate, directly or indirectly, the production of growth hormones from the pituitary gland, thereby complex genetics is involved. Defects in these genes are related to the deficiency of growth hormones solely, or deficiency of other hormones, secreted from the pituitary gland including growth hormones. These studies can aid clinicians to trace the pattern of the disease between the families, start early treatment and predict possible future consequences. This paper highlights some of the most common and novel genetic anomalies concerning growth hormones, which are responsible for various genetic defects in isolated growth and combined pituitary hormone deficiency 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.

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.

Unique near-complete deletion of GLI2 in a patient with combined pituitary hormone deficiency and post-axial polydactyly

INTRODUCTION

Combined pituitary hormone deficiency (CPHD) can cause a broad spectrum of health problems, ranging from short stature only, to convulsions or even death. In the majority of patients, the cause is unknown.

METHODS

The idex case had unexplained CPHD, pituitary anomalies on MRI and polydactyly. In the patients and her unaffected parents, we performed SNP array analysis and Whole Exome Sequencing, after candidate gene analysis turned out negative.

RESULTS

We found a unique de novo heterozygous 229.9 kb deletion in the index case on chr. 2q14.2. This deletion covered 12 out of the 13 coding exons of the GLI2 gene, a transcription factor involved in midline formation and previously associated with CPHD. As reported GLI2 deletions and mutations show a large phenotypic variability, we performed a genotype-phenotype analysis. This revealed that GLI2 missense mutations usually present with a 'ppp-only' phenotype (pituitary anomalies ± postaxial polydactyly without brain phenotype), whereas the 'ppp-plus' phenotype (with major brain malformations and/or intellectual disabilities) is more frequent in patients with larger deletions, and those with frameshift mutations/point mutations or splice variants resulting in a stop codon (p < .001).

CONCLUSION

The present case shows that a deletion of the GLI2 gene only (not affecting any of the adjacent genes) causes pituitary anomalies without brain phenotype. This suggests that brain phenotype only occurs when additional genes adjacent to GLI2 are deleted, or when mutations result in truncated GLI2 mRNA/protein. However, due to the lack of functional data for many GLI2 mutations and based on the available information regarding variable penetrance, phenotype-genotype correlations need to be made with caution.

Genetic causes of hypopituitarism

Hypopituitarism in neonates is rare, but has life-threatening complications if untreated. This review describes the features of hypopituitarism and the evidence for which infants in whom a genetic cause should be suspected. Importantly, neonates are often asymptomatic or present with non-specific symptoms. Hypopituitarism can be due to abnormal gland development as a result of genetic defects, which result from mutations in gene coding for transcription factors which regulate pituitary development. The mutations can be divided into those causing isolated hypopituitarism or those causing syndromes with associated hypopituitarism. The latter involve mutations in transcription factors which regulate pituitary, as well as extra-pituitary development. There is a paucity of evidence as to which patients should be investigated for genetic mutations, but detailed clinical and biochemical phenotyping with magnetic resonance imaging of the pituitary gland could help target those in whom genetic investigations would be most appropriate.

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.

Genetic diagnosis of congenital hypopituitarism by a target gene panel: novel pathogenic variants in GLI2, OTX2 and GHRHR

AIM

Congenital hypopituitarism has an incidence of 1:3500-10,000 births and is defined by the impaired production of pituitary hormones. Early diagnosis has an impact on management and genetic counselling. The clinical and genetic heterogeneity of hypopituitarism poses difficulties to select the order of genes to analyse. The objective of our study is to screen hypopituitarism genes (candidate and previously related genes) simultaneously using a target gene panel in patients with congenital hypopituitarism.

METHODS

Screening of 117 subjects with congenital hypopituitarism for pathogenic variants in 26 genes associated with congenital hypopituitarism by massively parallel sequencing using a customized target gene panel.

RESULTS

We found three novel pathogenic variants in OTX2 c.295C>T:p.Gln99*, GLI2 c.1681G>T:p.Glu561* and GHRHR c.820_821insC:p.Asp274Alafs*113, and the previously reported variants in GHRHR c.57+1G>A and PROP1 [c.301_302delAG];[c.109+1G>A].

CONCLUSIONS

Our results indicate that a custom-designed panel is an efficient method to screen simultaneously variants of biological and clinical relevance for congenital GH deficiency. A genetic diagnosis was possible in 5 out of 117 (4%) patients of our cohort. We identified three novel pathogenic variants in GHRHR, OTX2 and GLI2 expanding the spectrum of variants associated with congenital hypopituitarism.

A novel GLI2 mutation responsible for congenital hypopituitarism and polymalformation syndrome

OBJECTIVE

We report a novel GLI2 frameshift mutation and describe the phenotypic spectrum of mutations within this gene.

PATIENTS AND METHODS

A male with congenital hypopituitarism and polymalformation syndrome was clinically, biochemically and neuroradiologically characterized. Genetic analysis for congenital hypopituitarism was performed using a targeted NGS custom gene panel.

RESULTS

A heterozygous frameshift mutation, NM_005270.4:c.2125del, p.(Leu709Trpfs*15), was identified in GLI2 exon 12. This mutation has not been previously reported and confirms the diagnosis of Culler-Jones syndrome (MIM #615849).

CONCLUSION

GLI2 mutations should be suspected in the presence of congenital hypopitutarism, characteristic facial abnormalities and polydactyly.

A novel truncating variant of GLI2 associated with Culler-Jones syndrome impairs Hedgehog signalling

Background

GLI2 encodes for a transcription factor that controls the expression of several genes in the Hedgehog pathway. Mutations in GLI2 have been described as causative of a spectrum of clinical phenotypes, notably holoprosencephaly, hypopituitarism and postaxial polydactyl.

Methods

In order to identify causative genetic variant, we performed exome sequencing of a trio from an Italian family with multiple affected individuals presenting clinical phenotypes in the Culler-Jones syndrome spectrum. We performed a series of cell-based assays to test the functional properties of mutant GLI2.

Results

Here we report a novel deletion c.3493delC (p.P1167LfsX52) in the C-terminal activation domain of GLI2. Functional assays confirmed the pathogenicity of the identified variant and revealed a dominant-negative effect of mutant GLI2 on Hedgehog signalling.

Conclusions

Our results highlight the variable clinical manifestation of GLI2 mutations and emphasize the value of functional characterisation of novel gene variants to assist genetic counselling and diagnosis.

Molecular Mechanisms Governing Embryonic Differentiation of Pituitary Somatotropes

Pituitary somatotropes secrete growth hormone (GH), which is essential for normal growth and metabolism. Somatotrope defects result in GH deficiency (GHD), leading to short stature in childhood and increased cardiovascular morbidity and mortality in adulthood. Current hormone replacement therapies fail to recapitulate normal pulsatile GH secretion. Stem cell therapies could overcome this problem but are dependent on a thorough understanding of somatotrope differentiation. Although several transcription factors, signaling pathways, and hormones that regulate this process have been identified, the mechanisms of action are not well understood. The purpose of this review is to highlight the known players in somatotrope differentiation while emphasizing the need to better understand these pathways to serve patients with GHD.

GLI1 inactivation is associated with developmental phenotypes overlapping with Ellis-van Creveld syndrome

GLI1, GLI2 and GLI3 form a family of transcription factors which regulate development by mediating the action of Hedgehog (Hh) morphogens. Accordingly, inactivating variants in GLI2 and GLI3 are found in several developmental disorders. In contrast, loss-of-function mutations in GLI1 have remained elusive, maintaining enigmatic the role of this gene in the human embryo. We describe eight patients from three independent families having biallelic truncating variants in GLI1 and developmental defects overlapping with Ellis-van Creveld syndrome (EvC), a disease caused by diminished Hh signaling. Two families had mutations in the last exon of the gene and a third family was identified with an N-terminal stop gain variant predicted to be degraded by the NMD-pathway. Analysis of fibroblasts from one of the patients with homozygous C-terminal truncation of GLI1 demonstrated that the corresponding mutant GLI1 protein is fabricated by patient cells and becomes upregulated in response to Hh signaling. However, the transcriptional activity of the truncated GLI1 factor was found to be severely impaired by cell culture and in vivo assays, indicating that the balance between GLI repressors and activators is altered in affected subjects. Consistent with this, reduced expression of the GLI target PTCH1 was observed in patient fibroblasts after chemical induction of the Hh pathway. We conclude that GLI1 inactivation is associated with a phenotypic spectrum extending from isolated postaxial polydactyly to an EvC-like condition.

Holoprosencephaly in the genomics era

Holoprosencephaly (HPE) is the direct consequence of specific genetic and/or environmental insults interrupting the midline specification of the nascent forebrain. Such disturbances can lead to a broad range of phenotypic consequences for the brain and face in humans. This malformation sequence is remarkably common in utero (1 in 250 human fetuses), but 97% typically do not survive to birth. The precise molecular pathogenesis of HPE in these early human embryos remains largely unknown. Here, we outline our current understanding of the principal driving factors leading to HPE pathologies and elaborate our multifactorial integrated genomics approach. Overall, our understanding of the pathogenesis continues to become simpler, rather than more complicated. Genomic technologies now provide unprecedented insight into disease-associated variation, including the overall extent of genetic interactions (coding and noncoding) predicted to explain divergent phenotypes.

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.

Clues for Polygenic Inheritance of Pituitary Stalk Interruption Syndrome From Exome Sequencing in 20 Patients

CONTEXT

Pituitary stalk interruption syndrome (PSIS) consists of a small/absent anterior pituitary lobe, an interrupted/absent pituitary stalk, and an ectopic posterior pituitary lobe. Mendelian forms of PSIS are detected infrequently (<5%), and a polygenic etiology has been suggested. GLI2 variants have been reported at a relatively high frequency in PSIS.

OBJECTIVE

To provide further evidence for a non-Mendelian, polygenic etiology of PSIS.

METHODS

Exome sequencing (trio approach) in 20 patients with isolated PSIS. In addition to searching for (potentially) pathogenic de novo and biallelic variants, a targeted search was performed in a panel of genes associated with midline brain development (223 genes). For GLI2 variants, both (potentially) pathogenic and relatively rare variants (<5% in the general population) were studied. The frequency of GLI2 variants was compared with that of a reference population.

RESULTS

We found four additional candidate genes for isolated PSIS (DCHS1, ROBO2, CCDC88C, and KIF14) and one for syndromic PSIS (KAT6A). Eleven GLI2 variants were present in six patients. A higher frequency of a combination of two GLI2 variants (M1352V + D1520N) was found in the study group compared with a reference population (10% vs 0.68%). (Potentially) pathogenic variants were identified in genes associated with midline brain anomalies, including holoprosencephaly, hypogonadotropic hypogonadism, and absent corpus callosum and in genes involved in ciliopathies.

CONCLUSION

Combinations of variants in genes associated with midline brain anomalies are frequently present in PSIS and sustain the hypothesis of a polygenic cause of PSIS.

A novel heterozygous GLI2 mutation in a patient with congenital urethral stricture and renal hypoplasia/dysplasia leading to end-stage renal failure

Glioblastoma 2 (GLI2) is a mediator of Sonic hedgehog signaling pathway that plays an important role in development of the central nervous system and limbs. Heterozygous GLI2 mutations have been associated with postaxial polydactyly, various pituitary dysfunction, and holoprosencephaly-like phenotype. Herein, we report a Japanese boy who presented with isolated growth hormone deficiency with ectopic posterior pituitary, postaxial polydactyly, atrioventricular septal defect, intellectual disability and dysmorphic facial features including mid-facial hypoplasia. The patient was also complicated with congenital urethral stricture with megacystis, hydronephrosis, and renal hypoplasia/dysplasia, which led to end-stage renal failure by the age of 8 years. Trio-whole-exome sequencing showed a novel de novo heterozygous frameshift mutation in GLI2 (c.3369delG, p.Met1123Ilefs*7) in the patient. This is the first report of possible association between GLI2 mutation and the phenotype of congenital anomalies of the kidney and urinary tract, and subsequent end-stage renal failure. Further studies on the urogenital phenotype in patients with GLI2 mutations may clarify a role of GLI2 in embryonic development of the urinary tract.

Human Malformation Syndromes of Defective GLI: Opposite Phenotypes of 2q14.2 (GLI2) and 7p14.2 (GLI3) Microdeletions and a GLIA/R Balance Model

GLI family zinc finger proteins are transcriptional effectors of the sonic hedgehog signaling pathway. GLI regulates gene expression and repression at various phases of embryonic morphogenesis. In humans, 4 GLI genes are known, and GLI2 (2q14.2) and GLI3 (7p14.1) mutations cause different syndromes. Here, we present 2 distinctive cases with a chromosomal microdeletion in one of these genes. Patient 1 is a 14-year-old girl with Culler-Jones syndrome. She manifested short stature, cleft palate, and mild intellectual/social disability caused by a 6.6-Mb deletion of 2q14.1q14.3. Patient 2 is a 2-year-old girl with Greig cephalopolysyndactyly contiguous gene deletion syndrome. She manifested macrocephaly, preaxial polysyndactyly, psychomotor developmental delay, cerebral cavernous malformations, and glucose intolerance due to a 6.2-Mb deletion of 7p14.1p12.3 which included GLI3, GCK, and CCM2. Each patient manifests a different phenotype which is associated with different functions of each GLI gene and different effects of the chromosomal contiguous gene deletion. We summarize the phenotypic extent of GLI2/3 syndromes in the literature and determine that these 2 syndromes manifest opposite features to a certain extent, such as midface hypoplasia or macrocephaly, and anterior or posterior side of polydactyly. We propose a GLIA/R balance model that may explain these findings.

International multi-centre study of pregnancy outcomes with interleukin-1 inhibitors

Objective

To provide outcome data concerning pregnancies exposed to the Interleukin-1 (IL-1) inhibitors prior to conception in both men and women, during pregnancy and breast feeding.

Methods

Retrospective data were collected from members of the International Society for Systemic Autoinflammatory diseases and collated in a single centre. A uniform data collection sheet was used to obtain standardized data including maternal age and diagnosis, type, duration of and response to IL-1 blockade, pregnancy duration, delivery, mode of feeding and neonatal development.

Results

There were 31 maternal-exposed pregnancies from seven countries and we report the first data on paternal exposure: six to anakinra and five to canakinumab, with no negative outcomes. We also report the first data on canakinumab-exposed pregnancies: eight pregnancies that resulted in the delivery of seven healthy infants of normal gestational age and birthweight. There were 23 anakinra-exposed pregnancies resulting in the birth of 21 healthy infants, and one baby with unilateral renal agenesis and ectopic neurohypophysis. There were two first trimester miscarriages affecting a mother with active disease. There were no serious neonatal infections. Fourteen infants were breast fed with no complications. There were no reports of developmental delay, with follow-up of up to 10 years (median 18 months).

Conclusion

This series substantially increases the published experience of IL-1 blockade and reproduction including the first data on canakinumab and on paternal exposure to these agents. Data are generally reassuring, although the case of renal agenesis is the second reported in an anakinra-exposed pregnancy.

Human germline hedgehog pathway mutations predispose to fatty liver

BACKGROUND & AIMS

Non-alcoholic fatty liver disease (NAFLD) is the most common form of liver disease. Activation of hedgehog (Hh) signaling has been implicated in the progression of NAFLD and proposed as a therapeutic target; however, the effects of Hh signaling inhibition have not been studied in humans with germline mutations that affect this pathway.

METHODS

Patients with holoprosencephaly (HPE), a disorder associated with germline mutations disrupting Sonic hedgehog (SHH) signaling, were clinically evaluated for NAFLD. A combined mouse model of Hh signaling attenuation (Gli2 heterozygous null: Gli2^+/-) and diet-induced NAFLD was used to examine aspects of NAFLD and hepatic gene expression profiles, including molecular markers of hepatic fibrosis and inflammation.

RESULTS

Patients with HPE had a higher prevalence of liver steatosis compared to the general population, independent of obesity. Exposure of Gli2^+/- mice to fatty liver-inducing diets resulted in increased liver steatosis compared to wild-type mice. Similar to humans, this effect was independent of obesity in the mutant mice and was associated with decreased expression of pro-fibrotic and pro-inflammatory genes, and increased expression of PPARγ, a potent anti-fibrogenic and anti-inflammatory regulator. Interestingly, tumor suppressors p53 and p16INK4 were found to be downregulated in the Gli2^+/- mice exposed to a high-fat diet.

CONCLUSIONS

Our results indicate that germline mutations disrupting Hh signaling promotes liver steatosis, independent of obesity, with reduced fibrosis. While Hh signaling inhibition has been associated with a better NAFLD prognosis, further studies are required to evaluate the long-term effects of mutations affecting this pathway. Lay summary: Non-alcoholic fatty liver disease (NAFLD) is characterized by excess fat deposition in the liver predominantly due to high calorie intake and a sedentary lifestyle. NAFLD progression is usually accompanied by activation of the Sonic hedgehog (SHH) pathway leading to fibrous buildup (scar tissue) and inflammation of the liver tissue. For the first time patients with holoprosencephaly, a disease caused by SHH signaling mutations, are shown to have increased liver steatosis independent of obesity. This observation was recapitulated in a mouse model of attenuated SHH signaling that also showed increased liver steatosis but with decreased fibrosis and inflammation. While SHH inhibition is associated with a good NAFLD prognosis, this increase in liver fat accumulation in the context of SHH signaling inhibition must be studied prospectively to evaluate its long-term effects, especially in individuals with Western-type dietary habits.

Pituitary stem cell regulation: who is pulling the strings?

The pituitary gland plays a pivotal role in the endocrine system, steering fundamental processes of growth, metabolism, reproduction and coping with stress. The adult pituitary contains resident stem cells, which are highly quiescent in homeostatic conditions. However, the cells show marked signs of activation during processes of increased cell remodeling in the gland, including maturation at neonatal age, adaptation to physiological demands, regeneration upon injury and growth of local tumors. Although functions of pituitary stem cells are slowly but gradually uncovered, their regulation largely remains virgin territory. Since postnatal stem cells in general reiterate embryonic developmental pathways, attention is first being given to regulatory networks involved in pituitary embryogenesis. Here, we give an overview of the current knowledge on the NOTCH, WNT, epithelial-mesenchymal transition, SHH and Hippo pathways in the pituitary stem/progenitor cell compartment during various (activation) conditions from embryonic over neonatal to adult age. Most information comes from expression analyses of molecular components belonging to these networks, whereas functional extrapolation is still very limited. From this overview, it emerges that the 'big five' embryonic pathways are indeed reiterated in the stem cells of the 'lazy' homeostatic postnatal pituitary, further magnified en route to activation in more energetic, physiological and pathological remodeling conditions. Increasing the knowledge on the molecular players that pull the regulatory strings of the pituitary stem cells will not only provide further fundamental insight in postnatal pituitary homeostasis and activation, but also clues toward the development of regenerative ideas for improving treatment of pituitary deficiency and tumors.

Advances in understanding hypopituitarism

The understanding of hypopituitarism has increased over the last three years. This review provides an overview of the most important recent findings. Most of the recent research in hypopituitarism has focused on genetics. New diagnostic techniques like next-generation sequencing have led to the description of different genetic mutations causative for congenital dysfunction of the pituitary gland while new molecular mechanisms underlying pituitary ontogenesis have also been described. Furthermore, hypopituitarism may occur because of an impairment of the distinctive vascularization of the pituitary gland, especially by disruption of the long vessel connection between the hypothalamus and the pituitary. Controversial findings have been published on post-traumatic hypopituitarism. Moreover, autoimmunity has been discussed in recent years as a possible reason for hypopituitarism. With the use of new drugs such as ipilimumab, hypopituitarism as a side effect of pharmaceuticals has come into focus. Besides new findings on the pathomechanism of hypopituitarism, there are new diagnostic tools in development, such as new growth hormone stimulants that are currently being tested in clinical trials. Moreover, cortisol measurement in scalp hair is a promising tool for monitoring cortisol levels over time.

PITUITARY STALK INTERRUPTION SYNDROME: REPORT OF TWO CASES AND LITERATURE REVIEW

Pituitary stalk interruption syndrome (PSIS) consisting of the triad: ectopic posterior pituitary (EPP), thin or absent pituitary stalk and anterior pituitary hypoplasia is a rare pituitary malformation with variable degrees of pituitary insufficiency, from isolated growth hormone deficiency to TSH, gonadotropin and ACTH deficiency which may occur in time, with normo, hyper or hypoprolactinemia and central diabetes insipidus in up to 10% of cases. Also, extrapituitary malformations have been described in some cases. Genetic defects were identified only in 5% of cases. MRI findings are considered predictive for the endocrine phenotype. We aim to describe two cases with PSIS without central diabetes insipidus, anosmia and extrapituitary malformations, except for minor head dysmorphic features. The first case was referred at the age of 4 years for short stature (-4SDS for height, bone age 2 years), diagnosed with severe GH deficiency and developed central hypothyroidism and hypoprolactinemia during five-years follow-up. The second case, a 26 year old male with birth asphyxia, cryptorchidism, poor growth in childhood and adolescence (-3 to -4 height SDS), absent puberty and normal adult height (-1.18 SDS; bone age 15.5 years and active growth plates) had GH, TSH, ACTH deficiency and low normal PRL levels. Increasing medical awareness on PSIS clinical and endocrine heterogeneity may help a more early and accurate diagnosis. Corroboration of neuroimaging and endocrine data will improve our knowledge and understanding and will create premises for molecular diagnosis, genetic counseling and a better patients' management.

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.

MECHANISMS IN ENDOCRINOLOGY: An update in the genetic aetiologies of combined pituitary hormone deficiency

Over the last 5 years, new actors involved in the pathogenesis of combined pituitary hormone deficiency in humans have been reported: they included a member of the immunoglobulin superfamily glycoprotein and ciliary G protein-coupled receptors, as well as new transcription factors and signalling molecules. New modes of inheritance for alterations of genes encoding transcription factors have also been described. Finally, actors known to be involved in a very specific phenotype (hypogonadotroph hypogonadism for instance) have been identified in a wider range of phenotypes. These data thus suggest that new mechanisms could explain the low rate of aetiological identification in this heterogeneous group of diseases. Taking into account the fact that several reviews have been published in recent years on classical aetiologies of CPHD such as mutations of POU1F1 or PROP1, we focused the present overview on the data published in the last 5 years, to provide the reader with an updated review on this rapidly evolving field of knowledge.

Random monoallelic expression of genes on autosomes: Parallels with X-chromosome inactivation

Genes are generally expressed from their two alleles, except in some particular cases such as random inactivation of one of the two X chromosomes in female mammals or imprinted genes which are expressed only from the maternal or the paternal allele. A lesser-known phenomenon is random monoallelic expression (RME) of autosomal genes, where genes can be stably expressed in a monoallelic manner, from either one of the parental alleles. Studies on autosomal RME face several challenges. First, RME that is based on epigenetic mechanisms has to be distinguished from biased expression of one allele caused by a DNA sequence polymorphism in a regulatory element. Second, RME should not be confused with transient monoallelic expression often observed in single cell analyses, and that often corresponds to dynamic bursting of expression. Thanks to analyses on clonal cell populations, the existence of RME in cultured cells is now well established. Future studies of RME in vivo will have to overcome tissue heterogeneity and certain technical limitations. Here, we discuss current knowledge on autosomal RME, as well as possible mechanisms controlling these expression patterns and potential implications for development and disease, drawing parallels with what is known for X-chromosome inactivation, a paradigm of random monoallelic expression.