Molecular and Clinical Findings in Patients with LHX4 and OTX2 Mutations

The Genetic Backdrop of Hypogonadotropic Hypogonadism

The pituitary is an organ of dual provenance: the anterior lobe is epithelial in origin, whereas the posterior lobe derives from the neural ectoderm. The pituitary gland is a pivotal element of the axis regulating reproductive function in mammals. It collects signals from the hypothalamus, and by secreting gonadotropins (FSH and LH) it stimulates the ovary into cyclic activity resulting in a menstrual cycle and in ovulation. Pituitary organogenesis is comprised of three main stages controlled by different signaling molecules: first, the initiation of pituitary organogenesis and subsequent formation of Rathke’s pouch; second, the migration of Rathke’s pouch cells and their proliferation; and third, lineage determination and cellular differentiation. Any disruption of this sequence, e.g., gene mutation, can lead to numerous developmental disorders. Gene mutations contributing to disordered pituitary development can themselves be classified: mutations affecting transcriptional determinants of pituitary development, mutations related to gonadotropin deficiency, mutations concerning the beta subunit of FSH and LH, and mutations in the DAX-1 gene as a cause of adrenal hypoplasia and disturbed responsiveness of the pituitary to GnRH. All these mutations lead to disruption in the hypothalamic–pituitary–ovarian axis and contribute to the development of primary amenorrhea.

Congenital pituitary hypoplasia model demonstrates hypothalamic OTX2 regulation of pituitary progenitor cells

Pituitary develops from oral ectoderm in contact with adjacent ventral hypothalamus. Impairment in this process results in congenital pituitary hypoplasia (CPH); however, there have been no human disease models for CPH thus far, prohibiting the elucidation of the underlying mechanisms. In this study, we established a disease model of CPH using patient-derived induced pluripotent stem cells (iPSCs) and 3D organoid technique, in which oral ectoderm and hypothalamus develop simultaneously. Interestingly, patient iPSCs with a heterozygous mutation in the orthodenticle homeobox 2 (OTX2) gene showed increased apoptosis in the pituitary progenitor cells, and the differentiation into pituitary hormone-producing cells was severely impaired. As an underlying mechanism, OTX2 in hypothalamus, not in oral ectoderm, was essential for progenitor cell maintenance by regulating LHX3 expression in oral ectoderm via FGF10 expression in the hypothalamus. Convincingly, the phenotype was reversed by the correction of the mutation, and the haploinsufficiency of OTX2 in control iPSCs revealed a similar phenotype, demonstrating that this mutation was responsible. Thus, we established an iPSC-based congenital pituitary disease model, which recapitulated interaction between hypothalamus and oral ectoderm and demonstrated the essential role of hypothalamic OTX2.

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.

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.

Genetics of anophthalmia and microphthalmia. Part 1: Non-syndromic anophthalmia/microphthalmia

Eye formation is the result of coordinated induction and differentiation processes during embryogenesis. Disruption of any one of these events has the potential to cause ocular growth and structural defects, such as anophthalmia and microphthalmia (A/M). A/M can be isolated or occur with systemic anomalies, when they may form part of a recognizable syndrome. Their etiology includes genetic and environmental factors; several hundred genes involved in ocular development have been identified in humans or animal models. In humans, around 30 genes have been repeatedly implicated in A/M families, although many other genes have been described in single cases or families, and some genetic syndromes include eye anomalies occasionally as part of a wider phenotype. As a result of this broad genetic heterogeneity, with one or two notable exceptions, each gene explains only a small percentage of cases. Given the overlapping phenotypes, these genes can be most efficiently tested on panels or by whole exome/genome sequencing for the purposes of molecular diagnosis. However, despite whole exome/genome testing more than half of patients currently remain without a molecular diagnosis. The proportion of undiagnosed cases is even higher in those individuals with unilateral or milder phenotypes. Furthermore, even when a strong gene candidate is available for a patient, issues of incomplete penetrance and germinal mosaicism make diagnosis and genetic counseling challenging. In this review, we present the main genes implicated in non-syndromic human A/M phenotypes and, for practical purposes, classify them according to the most frequent or predominant phenotype each is associated with. Our intention is that this will allow clinicians to rank and prioritize their molecular analyses and interpretations according to the phenotypes of their patients.

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.

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.

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.

Heterogeneous phenotype in children affected by non-autoimmune hypothyroidism: an update

BACKGROUND

In the last decades, a higher incidence of congenital hypothyroidism (CH) has been recorded in Italy (1:1940) and worldwide, mainly due to the shift to lower screening TSH cutoffs. Although CH can also be caused by dysgenetic defects, most CH cases have recently been found to be more frequently associated with functional defects of an in situ thyroid gland. Although the clinical phenotype is milder with high prevalence of transient forms, some cases eventually prove to be permanent.

RESULTS

Possible explanations of the raised incidence of CH are ethnic modifications of the screened population and the increasing incidence of preterm birth and multiple pregnancies. These findings are important in terms of public health and standardization of screening programmes for special at-risk categories such as preterms, acutely ill term neonates, low birth weight and very low birth weight infants, and newborns with specific drug exposure. Other environmental factors have contributed to the increased incidence of hypothyroidism, including thyroid disrupting chemicals, iodine supply (excess/deficiency), and drugs interfering with thyroid function. Finally, an increased prevalence of hypothyroidism has been documented in obese children and patients with syndromic forms (Williams, Down, Turner, pseudohypoparathyroidism). The clinical and molecular phenotype of patients with CH will be better defined thanks to novel genetic approach based on the systematic analysis of a panel of genes (TSHR, DUOX2, DUOXA, TPO, PDS, TG, NKX2.1, JAG1, GLIS3, FOXE1, PAX-8).

CONCLUSIONS

This review summarizes significant advances in the epidemiology and aetiology of non-autoimmune hypothyroidism, with a focus on thyroid dysfunction in preterm infants.

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.

Neonatal screening and a new cause of congenital central hypothyroidism

Congenital central hypothyroidism (C-CH) is a rare disease in which thyroid hormone deficiency is caused by insufficient thyrotropin (TSH) stimulation of a normally-located thyroid gland. Most patients with C-CH have low free thyroxine levels and inappropriately low or normal TSH levels, although a few have slightly elevated TSH levels. Autosomal recessive TSH deficiency and thyrotropin-releasing hormone receptor-inactivating mutations are known to be genetic causes of C-CH presenting in the absence of other syndromes. Recently, deficiency of the immunoglobulin superfamily member 1 (IGSF1) has also been demonstrated to cause C-CH. IGSF1 is a plasma membrane glycoprotein highly expressed in the pituitary. Its physiological role in humans remains unknown. IGSF1 deficiency causes TSH deficiency, leading to hypothyroidism. In addition, approximately 60% of patients also suffer a prolactin deficiency. Moreover, macroorchidism and delayed puberty are characteristic features. Thus, although the precise pathophysiology of IGSF1 deficiency is not established, IGSF1 is considered to be a new factor controlling growth and puberty in children.