The IGSF1 deficiency syndrome: characteristics of male and female patients

Hypothalamic hormone deficiency enables physiological anorexia

Mammalian hibernators survive prolonged periods of cold and resource scarcity by temporarily modulating normal physiological functions, but the mechanisms underlying these adaptations are poorly understood. The hibernation cycle of thirteen-lined ground squirrels (Ictidomys tridecemlineatus) lasts for 5-7 months and comprises weeks of hypometabolic, hypothermic torpor interspersed with 24-48-hour periods of an active-like interbout arousal (IBA) state. We show that ground squirrels, who endure the entire hibernation season without food, have negligible hunger during IBAs. These squirrels exhibit reversible inhibition of the hypothalamic feeding center, such that hypothalamic arcuate nucleus neurons exhibit reduced sensitivity to the orexigenic and anorexigenic effects of ghrelin and leptin, respectively. However, hypothalamic infusion of thyroid hormone during an IBA is sufficient to rescue hibernation anorexia. Our results reveal that thyroid hormone deficiency underlies hibernation anorexia and demonstrate the functional flexibility of the hypothalamic feeding center.

Rare case of central congenital hypothyroidism due to a TSHβ mutation presenting with macro-orchidism

A male infant was brought to our paediatric endocrine unit with typical clinical features of congenital hypothyroidism (CH) and striking macro-orchidism. On evaluation, free T3, free T4 and thyroid stimulating hormone (TSH) were found to be low, suggestive of congenital CH. Cortisol was within reference range and prolactin was mildly elevated. No suspicious lesions were encountered on neurosonography. On commencing treatment with thyroxine, clinical features of hypothyroidism showed dramatic improvement with regression of testicular enlargement. Genetic analysis revealed deletion of the TSHβ gene.Our case highlights a rare presentation of central CH with macro-orchidism in a genetically proven deletion of TSHβ gene. Macro-orchidism has been widely reported in IGSF-1 mutations leading to central CH; however, central CH and macro-orchidism have not been reported in association with TSHβ deletions.

Hepatomegaly and fatty liver disease secondary to central hypothyroidism in combination with macrosomia as initial presentation of IGSF1 deficiency syndrome

PURPOSE

IGSF1 deficiency syndrome (immunoglobulin superfamily member 1) is considered the most common sex-linked cause of secondary congenital hypothyroidism and is characterized by a wide variety of other clinical and biochemical features, including hypoprolactinemia, transient and partial growth hormone deficiency, early/normal timing of testicular enlargement but delayed testosterone rise in puberty, and adult macro-orchidism. Congenital central hypothyroidism is a rare disease (1:65,000 births); the detection of which may be delayed and missed by neonatal screening programs since most neonatal screening programs are based on TSH determination in dried blood spots only. Untreated hypothyroidism may cause abnormal liver biochemistry and non-alcoholic fatty liver disease. Our aim is to report a case of secondary hypothyroidism in an infant with an uncommon initial presentation.

CASE PRESENTATION (METHODS/RESULTS)

A 3-month-old male baby was referred to our hospital due to elevated alpha-fetoprotein levels, hypercholesterolemia, and macrosomia. Initial investigations revealed enlarged fatty liver and central hypothyroidism. Pituitary insufficiency was biochemically excluded and a pituitary MRI showed normal findings. Upon genetic analysis, a hemizygous variant NM_001170961.1:c.2422dup, p.(His808Profs*14), in IGSF1 gene was detected, establishing the diagnosis of the IGSF1 deficiency syndrome. In our patient, no other clinical findings were identified. Treatment with levothyroxine led to the remission of liver disease.

CONCLUSION

Liver disease may be the initial presentation of secondary hypothyroidism in neonates and infants. Macrosomia in patients with isolated secondary central hypothyroidism is a strong indicator of IGSF1 syndrome.

IGSF1 mutations are the most frequent genetic aetiology of thyrotropin deficiency

DESIGN

Thyroid-stimulating hormone deficiency (TSHD) is a rare disease. It may be isolated, secondary to abnormalities of genes involved in TSH biosynthesis, or associated with other pituitary deficits or abnormalities of genes involved in pituitary ontogenesis. Several genes are involved in thyrotroph development and function.

OBJECTIVE

Our aim was to determine the genetic causes of TSHD, either isolated (ITSHD) or associated with somatotroph deficiency (TSHD-GHD), in the cohort of patients from the GENHYPOPIT network.

METHODS

Next-generation sequencing (NGS) analyses were performed as a panel of genes on a cohort of patients with non-syndromic ITSHD or TSHGHD. The variants were classified according to the American College of Medical Genetics classification reviewed by the NGS-Diag network and correlated with the phenotype. Class 3, 4, and 5 single-nucleotide variants were checked by Sanger sequencing and copy number variants by multiplex ligation-dependent probe amplification (MLPA).

RESULTS

A total of 64 index cases (22 ITSHD and 42 TSHD-GHD) were included in this cohort. A genetic cause was identified in 26.5% of patients, with 36.3% in the ITSHD group (variants in TSHβ and IGSF1) and 21.4% in TSHD-GHD (variants in IGSF1, TSHβ, TRHR, GH1, POU1F1, and PROP1). Among the pathogenic and likely pathogenic variants identified, 42% were in IGSF1, including six not previously reported.

CONCLUSION

Our results show that IGSF1 variants represent the most frequent aetiology of TSH deficiency. Despite a systematic NGS approach and the identification of new variants, most patients remain without a molecular diagnosis. Larger scale studies, such as exome or genome studies, should be considered in the future.

IGSF1 Deficiency Leads to Reduced TSH Production Independent of Alterations in Thyroid Hormone Action in Male Mice

Loss of function mutations in IGSF1/Igsf1 cause central hypothyroidism. Igsf1 knockout mice have reduced pituitary thyrotropin-releasing hormone receptor, Trhr, expression, perhaps contributing to the phenotype. Because thyroid hormones negatively regulate Trhr, we hypothesized that IGSF1 might affect thyroid hormone availability in pituitary thyrotropes. Consistent with this idea, IGSF1 coimmunoprecipitated with the thyroid hormone transporter monocarboxylate transporter 8 (MCT8) in transfected cells. This association was impaired with IGSF1 bearing patient-derived mutations. Wild-type IGSF1 did not, however, alter MCT8-mediated thyroid hormone import into heterologous cells. IGSF1 and MCT8 are both expressed in the apical membrane of the choroid plexus. However, MCT8 protein levels and localization in the choroid plexus were unaltered in Igsf1 knockout mice, ruling out a necessary chaperone function for IGSF1. MCT8 expression was low in the pituitary and was similarly unaffected in Igsf1 knockouts. We next assessed whether IGSF1 affects thyroid hormone transport or action, by MCT8 or otherwise, in vivo. To this end, we treated hypothyroid wild-type and Igsf1 knockout mice with exogenous thyroid hormones. T4 and T3 inhibited TSH release and regulated pituitary and forebrain gene expression similarly in both genotypes. Interestingly, pituitary TSH beta subunit (Tshb) expression was consistently reduced in Igsf1 knockouts relative to wild-type regardless of experimental condition, whereas Trhr was more variably affected. Although IGSF1 and MCT8 can interact in heterologous cells, the physiological relevance of their association is not clear. Nevertheless, the results suggest that IGSF1 loss can impair TSH production independently of alterations in TRHR levels or thyroid hormone action.

The extant immunoglobulin superfamily, member 1 gene results from an ancestral gene duplication in eutherian mammals

Immunoglobulin superfamily, member 1 (IGSF1) is a transmembrane glycoprotein with high expression in the mammalian pituitary gland. Mutations in the IGSF1 gene cause congenital central hypothyroidism in humans. The IGSF1 protein is co-translationally cleaved into N- and C-terminal domains (NTD and CTD), the latter of which is trafficked to the plasma membrane and appears to be the functional portion of the molecule. Though the IGSF1-NTD is retained in the endoplasmic reticulum and has no apparent function, it has a high degree of sequence identity with the IGSF1-CTD and is conserved across mammalian species. Based upon phylogenetic analyses, we propose that the ancestral IGSF1 gene encoded the IGSF1-CTD, which was duplicated and integrated immediately upstream of itself, yielding a larger protein encompassing the IGSF1-NTD and IGSF1-CTD. The selective pressures favoring the initial gene duplication and subsequent retention of a conserved IGSF1-NTD are unresolved.

The IGSF1, Wnt5a, FGF14, and ITPR1 Gene Expression and Prognosis Hallmark of Prostate Cancer

Background

Prostate cancer is considered as the second leading cause of cancer related death in men worldwide and the third frequent cancer among Iranian men. Despite the use of PSA as the only biomarker for early diagnosis of prostate cancer, its application in clinical settings is under debate. Therefore, the introduction of new molecular markers for early detection of prostate cancer is needed.

Methods

In the present study we intended to evaluate the expression of IGSF1, Wnt5a, FGF14, and ITPR1 in prostate cancer specimens by real time PCR. Biopsy samples of 40 prostate cancer cases and 41 healthy Iranian men were compared to determine the relative gene expression of IGSF1, Wnt5a, FGF14, and ITPR1 by real time PCR.

Results

Our results showed that Wnt5a, FGF14, and IGSF1 were significantly overexpressed in the prostate cancer patients while the mean relative expression of ITPR1 showed a significant decrease in PCa samples compared to healthy controls.

Conclusion

According to results of the present study, the combination panel of IGSF1, Wnt5a, FGF14, and ITPR1 genes could be considered as potential genetic markers for prostate cancer diagnosis. However further studies on larger populations and investigating the clinicopathological relevance of these genes is needed.

Case Report: A Detailed Phenotypic Description of Patients and Relatives with Combined Central Hypothyroidism and Growth Hormone Deficiency Carrying IGSF1 Mutations

In recent years, variants in immunoglobulin superfamily member 1 (IGSF1) have been associated with congenital hypopituitarism. Initially, IGSF1 variants were only reported in patients with central hypothyroidism (CeH) and macroorchidism. Later on, IGSF1 variants were also reported in patients with additional endocrinopathies, sometimes without macroorchidism. We studied IGSF1 as a new candidate gene for patients with combined CeH and growth hormone deficiency (GHD). We screened 80 male and 14 female Dutch patients with combined CeH and GHD for variants in the extracellular region of IGSF1, and we report detailed biomedical and clinical data of index cases and relatives. We identified three variants in our patient cohort, of which two were novel variants of unknown significance (p.L570I and c.1765+37C>A). In conclusion, we screened 94 patients with CeH and GHD and found variants in IGSF1 of which p.L570I could be of functional relevance. We provide detailed phenotypic data of two boys with the p.C947R variant and their large family. The remarkable phenotype of some of the relatives sheds new light on the phenotypic spectrum of IGSF1 variants.

A Case of Congenital Central Hypothyroidism Caused by a Novel Variant (Gln1255Ter) in IGSF1 Gene

Loss-of-function mutations in the immunoglobulin superfamily, member 1 (IGSF1) gene cause X-linked central hypothyroidism, and therefore its mutation affects mainly males. Central hypothyroidism in males is the hallmark of the disorder, however some patients additionally present with hypoprolactinemia, transient and partial growth hormone deficiency, early/normal timing of testicular enlargement but delayed testosterone rise in puberty, and adult macro-orchidism. Here, we report a boy with congenital central hypothyroidism caused by a novel variant in the IGSF1 gene. In our patient, early testicular enlargement but delayed testosterone rise with central hypothyroidism and hypoprolactinemia were the most important clues for diagnosis. In genetic analysis, we identified a novel, hemizygous nonsense c.3763 C>T (G1n1255Ter) variant in IGSF1 gene. To our knowledge, this is the first reported case of IGSF1 deficiency from Turkey.

Dopaminergic organization of striatum is linked to cortical activity and brain expression of genes associated with psychiatric illness

Dopamine signaling is constrained to discrete tracts yet has brain-wide effects on neural activity. The nature of this relationship between local dopamine signaling and brain-wide neuronal activity is not clearly defined and has relevance for neuropsychiatric illnesses where abnormalities of cortical activity and dopamine signaling coexist. Using simultaneous PET-MRI in healthy volunteers, we find strong evidence that patterns of striatal dopamine signaling and cortical blood flow (an index of local neural activity) contain shared information. This shared information links amphetamine-induced changes in gradients of striatal dopamine receptor availability to changes in brain-wide blood flow and is informed by spatial patterns of gene expression enriched for genes implicated in schizophrenia, bipolar disorder, and autism spectrum disorder. These results advance our knowledge of the relationship between cortical function and striatal dopamine, with relevance for understanding pathophysiology and treatment of diseases in which simultaneous aberrations of these systems exist.

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.

Diagnosis and Management of Central Congenital Hypothyroidism

Central congenital hypothyroidism (CH) is defined as thyroid hormone (TH) deficiency at birth due to insufficient stimulation by the pituitary of the thyroid gland. The incidence of central CH is currently estimated at around 1:13,000. Central CH may occur in isolation, but in the majority of cases (60%) it is part of combined pituitary hormone deficiencies (CPHD). In recent years several novel genetic causes of isolated central CH have been discovered (IGSF1, TBL1X, IRS4), and up to 90% of isolated central CH cases can be genetically explained. For CPHD the etiology usually remains unknown, although pituitary stalk interruption syndrome does seem to be the most common anatomic pituitary malformation associated with CPHD. Recent studies have shown that central CH is a more severe condition than previously thought, and that early detection and treatment leads to good neurodevelopmental outcome. However, in the neonatal period the clinical diagnosis is often missed despite hospital admission because of feeding problems, hypoglycemia and prolonged jaundice. This review provides an update on the etiology and prognosis of central CH, and a practical approach to diagnosis and management of this intriguing condition.

Congenital isolated central hypothyroidism: Novel mutations and their functional implications

Congenital hypothyroidism is the most frequent endocrine disorder in newborns, occurring in 1 per 3000-4000 newborns. In the Netherlands, the neonatal screening program is based primarily on heel prick thyroxine (T4). In contrast to thyroid-stimulating hormone-based programs, this approach allows for the detection of both primary and central congenital hypothyroidism. Over the past decade, the identification of families with isolated congenital central hypothyroidism enabled the identification of novel genetic causes of this condition, in addition to mutations in the TSHβ-subunit gene and thyrotropin-releasing hormone receptor gene reported earlier. In 2012, loss-of-function mutations in the immunoglobulin superfamily, member 1 (IGSF1) gene, were reported as a genetic cause of a syndrome including X-linked congenital central hypothyroidism and adult macroorchidism. IGSF1 encodes a hypothalamic plasma membrane glycoprotein. Mutations in IGSF1 represent the most prevalent genetic cause of isolated central hypothyroidism to date. In 2016, mutations in the transducin β-like 1X (TBL1X) gene were identified in patients with a combination of mild central hypothyroidism and sensorineural hearing loss. TBL1X is an essential subunit of the NCoR/SMRT corepressor complex and expressed in many tissues including the human hypothalamus and pituitary. In 2018, mutations in the insulin receptor substrate 4 (IRS4) gene were reported in cases of familial isolated central hypothyroidism. IRS4 encodes a hypothalamic protein that is part of the insulin and leptin signaling cascade. These recent developments will broaden our understanding of the role of the hypothalamus in hypothalamus-pituitary-thyroid axis regulation and will help to improve diagnosis and treatment of isolated central hypothyroidism.

Lasting and Sex-Dependent Impact of Maternal Immune Activation on Molecular Pathways of the Amygdala

The prolonged and sex-dependent impact of maternal immune activation (MIA) during gestation on the molecular pathways of the amygdala, a brain region that influences social, emotional, and other behaviors, is only partially understood. To address this gap, we investigated the effects of viral-elicited MIA during gestation on the amygdala transcriptome of pigs, a species of high molecular and developmental homology to humans. Gene expression levels were measured using RNA-Seq on the amygdala for 3-week-old female and male offspring from MIA and control groups. Among the 403 genes that exhibited significant MIA effect, a prevalence of differentially expressed genes annotated to the neuroactive ligand-receptor pathway, glutamatergic functions, neuropeptide systems, and cilium morphogenesis were uncovered. Genes in these categories included corticotropin-releasing hormone receptor 2, glutamate metabotropic receptor 4, glycoprotein hormones, alpha polypeptide, parathyroid hormone 1 receptor, vasointestinal peptide receptor 2, neurotensin, proenkephalin, and gastrin-releasing peptide. These categories and genes have been associated with the MIA-related human neurodevelopmental disorders, including schizophrenia and autism spectrum disorders. Gene network reconstruction highlighted differential vulnerability to MIA effects between sexes. Our results advance the understanding necessary for the development of multifactorial therapies targeting immune modulation and neurochemical dysfunction that can ameliorate the effects of MIA on offspring behavior later in life.

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.

Hypoprolactinemia as a Clue to Diagnosis of Mild Central Hypothyroidism due to IGSF1 Deficiency

Loss-of-function mutations of IGSF1 are an X-linked cause of central hypothyroidism (CeH) and hypoprolactinemia. A boy who is now 15.2 years old presented at the age of 7.69 years for evaluation of obesity. Previous thyroid function evaluation suggested CeH [FT4 0.6 ng/mL, thyroid-stimulating hormone (TSH) 2.2 mIU/L] but his physician took no action. At presentation he was clinically and biochemically euthyroid, prepubertal and obese. Serum prolactin (PRL) was undetectable. Biochemistry was normal except for mild hypercholesterolemia, total cholesterol 198 mg/dL. Subsequently FT4 and TSH levels fluctuated between 0.72-0.95 ng/dL (normal 0.8-2.0) and 1.94-5.77 mIU/L (normal 0.3-5.0), respectively. Sequencing of IGSF1 gene revealed a novel genetic change c.3805C>T in exon 19; substitution of amino acid Arginine at position 1269 with a premature «stop» codon resulting in an altered protein product. The patient additionally presented delayed adrenarche, low height velocity that resolved spontaneously and normal pubertal onset associated with increased FSH levels. At 14 years-of-age, while the patient was at Tanner stage 4, PRL levels became detectable, rising gradually to 2.3 ng/mL at last examination. Thyroxine replacement therapy resulted in decrease in total cholesterol 103 mg/dL. A high index of suspicion for the disorder is needed since several measurements of thyroid function may be required for CeH to be disclosed. The patient’s normal FT4 levels and normal intelligence would have resulted in a missed diagnosis if the serum PRL levels had not been measured. This case highlights the importance of measuring PRL in a boy with low normal FT4 and normal TSH levels.

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.

IGSF1 Deficiency Results in Human and Murine Somatotrope Neurosecretory Hyperfunction

CONTEXT

The X-linked immunoglobulin superfamily, member 1 (IGSF1), gene is highly expressed in the hypothalamus and in pituitary cells of the POU1F1 lineage. Human loss-of-function mutations in IGSF1 cause central hypothyroidism, hypoprolactinemia, and macroorchidism. Additionally, most affected adults exhibit higher than average IGF-1 levels and anecdotal reports describe acromegaloid features in older subjects. However, somatotrope function has not yet been formally evaluated in this condition.

OBJECTIVE

We aimed to evaluate the role of IGSF1 in human and murine somatotrope function.

PATIENTS, DESIGN, AND SETTING

We evaluated 21 adult males harboring hemizygous IGSF1 loss-of-function mutations for features of GH excess, in an academic clinical setting.

MAIN OUTCOME MEASURES

We compared biochemical and tissue markers of GH excess in patients and controls, including 24-hour GH profile studies in 7 patients. Parallel studies were undertaken in male Igsf1-deficient mice and wild-type littermates.

RESULTS

IGSF1-deficient adult male patients demonstrated acromegaloid facial features with increased head circumference as well as increased finger soft-tissue thickness. Median serum IGF-1 concentrations were elevated, and 24-hour GH profile studies confirmed 2- to 3-fold increased median basal, pulsatile, and total GH secretion. Male Igsf1-deficient mice also demonstrated features of GH excess with increased lean mass, organ size, and skeletal dimensions and elevated mean circulating IGF-1 and pituitary GH levels.

CONCLUSIONS

We demonstrate somatotrope neurosecretory hyperfunction in IGSF1-deficient humans and mice. These observations define a hitherto uncharacterized role for IGSF1 in somatotropes and indicate that patients with IGSF1 mutations should be evaluated for long-term consequences of increased GH exposure.

Update on congenital hypothyroidism

PURPOSE OF REVIEW

The present review summarizes recent advances in the diagnosis and management of patients with congenital hypothyroidism.

RECENT FINDINGS

Although most newborn screening strategies are designed to detect severe primary hypothyroidism that presents shortly after birth, some infants display a pattern of delayed TSH rise despite normal initial newborn screening. Recent studies suggest that delayed TSH rise may be more common and more severe than previously recognized. Although much less common than primary hypothyroidism, central congenital hypothyroidism is as likely to be of moderate or severe degree, which has implications for its detection and treatment. The discovery of new genetic causes of central congenital hypothyroidism, including the X-linked genes IGSF1, TBL1X, and IRS4, has begun to expand our understanding of thyroid axis regulation. Recent long-term data indicate that current treatment recommendations for congenital hypothyroidism result in grossly normal neurocognitive outcomes even in severely affected patients, and that overtreatment may not be as harmful as previously suspected. Liquid levothyroxine is now commercially available in the United States, but more studies are needed to determine optimal dosing using this formulation.

SUMMARY

Prompt identification and adequate treatment of patients with congenital hypothyroidism is critical to optimize outcomes. New information continues to accumulate about how to improve detection of congenital hypothyroidism in specific subgroups of infants (particularly those with delayed TSH rise and central hypothyroidism) and about treatment of patients with this disorder.

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.

IGSF1: A novel oncogene regulates the thyroid cancer progression

Thyroid cancer has been continuously increasing and extraordinarily prevalent worldwide. The genetic diagnosis has been widely used in fine needle aspiration. IGSF1, an immunoglobulin superfamily member 1, has been shown to be associated with the regulation of thyroid hormone. But the function of IGSF1 in thyroid cancer has not been explored yet. In this article, we will illuminate the correlation between IGSF1 expression and thyroid cancer. We analysed the level of IGSF1 expression in 55 pairs of tissue samples by real-time polymerase chain reaction (PCR) and The Cancer Genome Atlas (TCGA) data portal. After that, we transfected small interfering RNA to silence IGSF1 in thyroid cancer cell lines (KTC-1 and BCPAP) and confirmed the function of IGSF1 by performed colony formation, migration, invasion, cell counting kit-8, and apoptosis assays. IGSF1 was upregulated in thyroid cancer tissues compared with the adjacent normal tissues (t = 5.783, df = 54; P < .0001) and TCGA (T: N = 65.91 ± 3.998, n = 501: 2.824 ± 0.273, n = 58; P < .0001). In thyroid cell lines, experiments showed that downregulated IGSF1 inhibited proliferation, metastasis, and promoted cell apoptosis. Meanwhile, inhibited IGSF1 expression could downregulate N-cadherin, vimentin, and EZH2, which is associated with metastasis. Thyroid cancer cells IGSF1 expression levels are a correlation with its ability to growth, metastasis, and apoptosis.

The diagnosis and management of central hypothyroidism in 2018

Central hypothyrodism (CeH) is a hypothyroid state caused by an insufficient stimulation by thyrotropin (TSH) of an otherwise normal thyroid gland. Several advancements, including the recent publication of expert guidelines for CeH diagnosis and management, have been made in recent years thus increasing the clinical awareness on this condition. Here, we reviewed the recent advancements and give expert opinions on critical issues. Indeed, CeH can be the consequence of various disorders affecting either the pituitary gland or the hypothalamus. Recent data enlarged the list of candidate genes for heritable CeH and a genetic origin may be the underlying cause for CeH discovered in pediatric or even adult patients without apparent pituitary lesions. This raises the doubt that the frequency of CeH may be underestimated. CeH is most frequently diagnosed as a consequence of the biochemical assessments in patients with hypothalamic/pituitary lesions. In contrast with primary hypothyroidism, low FT4 with low/normal TSH levels are the biochemical hallmark of CeH, and adequate thyroid hormone replacement leads to the suppression of residual TSH secretion. Thus, CeH often represents a clinical challenge because physicians cannot rely on the use of the 'reflex TSH strategy' for screening or therapy monitoring. Nevertheless, in contrast with general assumption, the finding of normal TSH levels may indicate thyroxine under-replacement in CeH patients. The clinical management of CeH is further complicated by the combination with multiple pituitary deficiencies, as the introduction of sex steroids or GH replacements may uncover latent forms of CeH or increase the thyroxine requirements.

A novel IGSF1 mutation in a large Irish kindred highlights the need for familial screening in the IGSF1 deficiency syndrome

OBJECTIVE

Loss-of-function mutations in IGSF1 result in X-linked central congenital hypothyroidism (CeCH), occurring in isolation or associated with additional pituitary hormone deficits. Intrafamilial penetrance is highly variable and a minority of heterozygous females are also affected. We identified and characterized a novel IGSF1 mutation and investigated its associated phenotypes in a large Irish kindred.

DESIGN, PATIENTS AND MEASUREMENTS

A novel hemizygous IGSF1 mutation was identified by direct sequencing in two brothers with CeCH, and its functional consequences were characterized in vitro. Genotype-phenotype correlations were investigated in the wider kindred.

RESULTS

The mutant IGSF1 protein (c.2318T > C, p.L773P) exhibited decreased plasma membrane expression in vitro due to impaired trafficking from the endoplasmic reticulum. Ten hemizygous males and 11 heterozygous females exhibited characteristic endocrine deficits. Ireland operates a TSH-based CH screening programme, which does not detect CeCH; therefore, genetic ascertainment preceded biochemical diagnosis of moderate CH in five of seven boys as well as their 75-year-old grandfather. Clinical features potentially attributable to hypothyroidism were variable; normal free T3 (FT3) and low/low normal reverse T3 (rT3) concentrations suggested that preferential deiodination of FT4 to FT3 may help maintain tissue euthyroidism in some individuals. However, neonatal jaundice, delayed speech or growth, and obesity were observed in seven subjects in whom diagnosis was delayed.

CONCLUSIONS

As observed with other IGSF1 mutations, p.L773P results in variably penetrant IGSF1 deficiency syndrome. Our observations emphasize the need for multi-generation genetic ascertainment in affected families, especially where TSH-based CH screening programmes may fail to detect CeCH at birth.

Less known aspects of central hypothyroidism: Part 2 - Congenital etiologies

Central hypothyroidism (CH) occurs approximately in 1:50,000, and therefore is expected to be one thousand times rarer compared with primary hypothyroidism. Despite its rarity in the general population, it is much more common in certain disorders, in which it is frequently associated with other pituitary hormone deficiencies. The aim of this paper is to provide an updated review on the frequency of congenital CH, which is <1:50,000, and on its etiology, disregarding CH caused by other genetic defects, such as mutations of transcription factors involved in pituitary organogenesis or mutations of the genes encoding TRH or TRH receptor.

Mortality in Children With Early-Detected Congenital Central Hypothyroidism

CONTEXT

Approximately 60% to 80% of patients with congenital central hypothyroidism (CH-C) have multiple pituitary hormone deficiencies (MPHDs), making CH-C a potentially life-threatening disease. Data on mortality in patients with CH-C are lacking.

OBJECTIVE

To study the mortality rate in pediatric patients with early-detected and treated CH-C in the Netherlands and to investigate whether causes of death were related to pituitary hormone deficiencies.

METHODS

Overall mortality rate, infant mortality rate (IMR), and under-5 mortality rate were calculated in all children with CH-C detected by neonatal screening between 1 January 1995 and 1 January 2013. Medical charts were reviewed to establish causes of death.

RESULTS

A total of 139 children with CH-C were identified, of which 138 could be traced (82 with MPHD, 56 with isolated CH-C). Total observation time was 1414 years with a median follow-up duration of 10.2 years. The overall mortality rate was 10.9% (15/138). IMR and under-5 mortality rate were 65.2/1000 (9/138) and 101.4/1000 (14/138), respectively, compared with an IMR of 4.7/1000 and under-5 mortality of 5.4/1000 live-born children in the Netherlands during the same time period (P < 0.0001). Main causes of death were severe congenital malformations in six patients, asphyxia in two patients, and congenital or early neonatal infection in two patients. Pituitary hormone deficiency was noted as cause of death in only one infant.

CONCLUSION

We report an increased mortality rate in patients with early-detected CH-C that does not seem to be related to endocrine disease. This suggests that mortality due to pituitary insufficiency is low in patients with early-detected and early-treated CH-C.

From Consternation to Revelation: Discovery of a Role for IGSF1 in Pituitary Control of Thyroid Function

Immunoglobulin superfamily, member 1 (IGSF1) is a transmembrane glycoprotein highly expressed in the mammalian pituitary gland. Shortly after its discovery in 1998, the protein was proposed to function as a coreceptor for inhibins (and was even temporarily renamed inhibin binding protein). However, subsequent investigations, both in vitro and in vivo, failed to support a role for IGSF1 in inhibin action. Research on IGSF1 nearly ground to a halt until 2011, when next-generation sequencing identified mutations in the X-linked IGSF1 gene in boys and men with congenital central hypothyroidism. IGSF1 was localized to thyrotrope cells, implicating the protein in pituitary control of the thyroid. Investigations in two Igsf1 knockout mouse models converged to show that IGSF1 deficiency leads to reduced expression of the receptor for thyrotropin-releasing hormone (TRH) and impaired TRH stimulation of thyrotropin secretion, providing a candidate mechanism for the central hypothyroidism observed in patients. Nevertheless, the normal functions of IGSF1 in thyrotropes and other cells remain unresolved. Moreover, IGSF1 mutations are also commonly associated with other clinical phenotypes, including prolactin and growth hormone dysregulation, and macroorchidism. How the loss of IGSF1 produces these characteristics is unknown. Although early studies of IGSF1 ran into roadblocks and blind alleys, armed with the results of detailed clinical investigations, powerful mouse models, and new reagents, the field is now poised to discover IGSF1’s function in endocrine tissues, including the pituitary and testes.

Congenital hypothyroidism: insights into pathogenesis and treatment

Congenital hypothyroidism occurs in approximately 1 in 2000 newborns and can have devastating neurodevelopmental consequences if not detected and treated promptly. While newborn screening has virtually eradicated intellectual disability due to severe congenital hypothyroidism in the developed world, more stringent screening strategies have resulted in increased detection of mild congenital hypothyroidism. Recent studies provide conflicting evidence about the potential neurodevelopmental risks posed by mild congenital hypothyroidism, highlighting the need for additional research to further define what risks these patients face and whether they are likely to benefit from treatment. Moreover, while the apparent incidence of congenital hypothyroidism has increased in recent decades, the underlying cause remains obscure in most cases. However, ongoing research into genetic causes of congenital hypothyroidism continues to shed new light on the development and physiology of the hypothalamic-pituitary-thyroid axis. The identification of IGSF1 as a cause of central congenital hypothyroidism has uncovered potential new regulatory pathways in both pituitary thyrotropes and gonadotropes, while mounting evidence suggests that a significant proportion of primary congenital hypothyroidism may be caused by combinations of rare genetic variants in multiple genes involved in thyroid development and function. Much remains to be learned about the origins of this common disorder and about the optimal management of less severely-affected infants.

Central hypothyroidism - a neglected thyroid disorder

Central hypothyroidism is a rare and heterogeneous disorder that is characterized by a defect in thyroid hormone secretion in an otherwise normal thyroid gland due to insufficient stimulation by TSH. The disease results from the abnormal function of the pituitary gland, the hypothalamus, or both. Moreover, central hypothyroidism can be isolated or combined with other pituitary hormone deficiencies, which are mostly acquired and are rarely congenital. The clinical manifestations of central hypothyroidism are usually milder than those observed in primary hypothyroidism. Obtaining a positive diagnosis for central hypothyroidism can be difficult from both a clinical and a biochemical perspective. The diagnosis of central hypothyroidism is based on low circulating levels of free T₄ in the presence of low to normal TSH concentrations. The correct diagnosis of both acquired (also termed sporadic) and congenital (also termed genetic) central hypothyroidism can be hindered by methodological interference in free T₄ or TSH measurements; routine utilization of total T₄ or T₃ measurements; concurrent systemic illness that is characterized by low levels of free T₄ and normal TSH concentrations; the use of the sole TSH-reflex strategy, which is the measurement of the sole level of TSH, without free T₄, if levels of TSH are in the normal range; and the diagnosis of congenital hypothyroidism based on TSH analysis without the concomitant measurement of serum levels of T₄. In this Review, we discuss current knowledge of the causes of central hypothyroidism, emphasizing possible pitfalls in the diagnosis and treatment of this disorder.

Pediatric Hypothyroidism: Diagnosis and Treatment

Thyroid hormone has important physiologic functions in nearly every organ system. The critical role of thyroid hormone in growth and in physical and neurologic development lends particular importance to the prompt diagnosis and appropriate treatment of hypothyroidism in infants and children. Congenital hypothyroidism is common and has potentially devastating neurologic consequences. While the approach to diagnosis and treatment of severe congenital hypothyroidism is well established, data continue to emerge about the genetic causes, clinical significance, and prognosis of the milder forms of congenital hypothyroidism that are increasingly being diagnosed by newborn screening. Similarly, the diagnosis and treatment of severe acquired hypothyroidism is straightforward and clearly of clinical benefit, but uncertainty remains about the optimal management of mild subclinical hypothyroidism. This review summarizes current knowledge of the causes, clinical manifestations, diagnosis, treatment, and prognosis of hypothyroidism in infants and children, with a focus on recent developments and areas of uncertainty in this field.

Appraisal of testicular volumes: volumes matching ultrasound values referenced to stages of genital development

Background

Testicular volumes obtained with orchidometers or external linear measurements in the scrotum (centimeter ruler or calipers) grossly over-estimate ultrasound volumes, have much variability and may not be accurate or reproducible. The reference of the values obtained by orchidometers or US, to age or Tanner stages is not useful to determine the normal values for stages of puberty, because overlapping of ages and values. Pubertal development is determined by two events, genital and pubic hair development, that should be analyzed independently because one could be out of step with the other. The ultrasound (US) measurement of testicular volumes is the gold standard but is somewhat inconvenient, because it requires another procedure and, mainly, is costly.

The solution of the problems would be to determine testicular volumes matching US values, from the width of the testis obtained in the scrotum with a centimeter ruler, by formulas recently described, and to reference them to the stages of genital development.

Methods

The width and length of the testes in the scrotum with a centimeter ruler were obtained in 159 study subjects, in different stages of genital development and adults, for a total of 318 testicular determinations, from the age of 3 to 34 years. The width obtained in the scrotum was corrected by subtracting the values of the double scrotal skin (ss). The formulas were then applied and the testicular volumes matching US values were calculated. The volumes and the range of ages for different stages of genital development were determined. Penile measurements were obtained in 145 subjects and pubic and other hair recorded.

Paired and unpaired 2 tail student t-test was used to compare the means of the different groups expressed as means and SD and, in addition the Wilcoxon rank sum test and Bootstrap methods for the testicular volume groups. A p value of 0.05 or less was considered significant.

The Institutional Review Board (IRB) of Nationwide Children’s Hospital determined that this study did not require IRB approval.

Results

With a simple measurement of the width of the testis in the scrotum, with a centimeter ruler, testicular volumes matching US values were calculated and normative values for each stage of genital development were determined.

Conclusion

This information should solve present problems.

Electronic supplementary material

The online version of this article (doi:10.1186/s13633-017-0046-x) contains supplementary material, which is available to authorized users.

The short mRNA isoform of the immunoglobulin superfamily, member 1 gene encodes an intracellular glycoprotein

Mutations in the immunoglobulin superfamily, member 1 gene (IGSF1/Igsf1) cause an X-linked form of central hypothyroidism. The canonical form of IGSF1 is a transmembrane glycoprotein with 12 immunoglobulin (Ig) loops. The protein is co-translationally cleaved into two sub-domains. The carboxyl-terminal domain (CTD), which contains the last 7 Ig loops, is trafficked to the plasma membrane. Most pathogenic mutations in IGSF1 map to the portion of the gene encoding the CTD. IGSF1/Igsf1 encodes a variety of transcripts. A little studied, but abundant splice variant encodes a truncated form of the protein, predicted to contain the first 2 Ig loops of the full-length IGSF1. The protein (hereafter referred to as IGSF1 isoform 2 or IGSF1-2) is likely retained in most individuals with IGSF1 mutations. Here, we characterized basic biochemical properties of the protein as a foray into understanding its potential function. IGSF1-2, like the IGSF1-CTD, is a glycoprotein. In both mouse and rat, the protein is N-glycosylated at a single asparagine residue in the first Ig loop. Contrary to earlier predictions, neither the murine nor rat IGSF1-2 is secreted from heterologous or homologous cells. In addition, neither protein associates with the plasma membrane. Rather, IGSF1-2 appears to be retained in the endoplasmic reticulum. Whether the protein plays intracellular functions or is trafficked through the secretory pathway under certain physiologic or pathophysiologic conditions has yet to be determined.

TRH Action Is Impaired in Pituitaries of Male IGSF1-Deficient Mice

Loss-of-function mutations in the X-linked immunoglobulin superfamily, member 1 (IGSF1) gene cause central hypothyroidism. IGSF1 is a transmembrane glycoprotein of unknown function expressed in thyrotropin (TSH)-producing thyrotrope cells of the anterior pituitary gland. The protein is cotranslationally cleaved, with only its C-terminal domain (CTD) being trafficked to the plasma membrane. Most intragenic IGSF1 mutations in humans map to the CTD. In this study, we used CRISPR-Cas9 to introduce a loss-of-function mutation into the IGSF1-CTD in mice. The modified allele encodes a truncated protein that fails to traffic to the plasma membrane. Under standard laboratory conditions, Igsf1-deficient males exhibit normal serum TSH levels as well as normal numbers of TSH-expressing thyrotropes. However, pituitary expression of the TSH subunit genes and TSH protein content are reduced, as is expression of the receptor for thyrotropin-releasing hormone (TRH). When challenged with exogenous TRH, Igsf1-deficient males release TSH, but to a significantly lesser extent than do their wild-type littermates. The mice show similarly attenuated TSH secretion when rendered profoundly hypothyroid with a low iodine diet supplemented with propylthiouracil. Collectively, these results indicate that impairments in pituitary TRH receptor expression and/or downstream signaling underlie central hypothyroidism in IGSF1 deficiency syndrome.

The syndrome of central hypothyroidism and macroorchidism: IGSF1 controls TRHR and FSHB expression by differential modulation of pituitary TGFβ and Activin pathways

IGSF1 (Immunoglobulin Superfamily 1) gene defects cause central hypothyroidism and macroorchidism. However, the pathogenic mechanisms of the disease remain unclear. Based on a patient with a full deletion of IGSF1 clinically followed from neonate to adulthood, we investigated a common pituitary origin for hypothyroidism and macroorchidism, and the role of IGSF1 as regulator of pituitary hormone secretion. The patient showed congenital central hypothyroidism with reduced TSH biopotency, over-secretion of FSH at neonatal minipuberty and macroorchidism from 3 years of age. His markedly elevated inhibin B was unable to inhibit FSH secretion, indicating a status of pituitary inhibin B resistance. We show here that IGSF1 is expressed both in thyrotropes and gonadotropes of the pituitary and in Leydig and germ cells in the testes, but at very low levels in Sertoli cells. Furthermore, IGSF1 stimulates transcription of the thyrotropin-releasing hormone receptor (TRHR) by negative modulation of the TGFβ1-Smad signaling pathway, and enhances the synthesis and biopotency of TSH, the hormone secreted by thyrotropes. By contrast, IGSF1 strongly down-regulates the activin-Smad pathway, leading to reduced expression of FSHB, the hormone secreted by gonadotropes. In conclusion, two relevant molecular mechanisms linked to central hypothyroidism and macroorchidism in IGSF1 deficiency are identified, revealing IGSF1 as an important regulator of TGFβ/Activin pathways in the pituitary.

The multiple genetic causes of central hypothyroidism

An insufficient stimulation by thyrotropin (TSH) of an otherwise normal thyroid gland represents the cause of Central Hypothyrodism (CeH). CeH is about 1000-folds rarer than Primary Hypothyroidism and often represents a real challenge for the clinicians, mainly because they cannot rely on adequately sensitive parameters for diagnosis or management, as it occurs with circulating TSH in PH. Therefore, CeH diagnosis can be frequently missed or delayed in patients with a previously unknown pituitary involvement. A series of genetic defects have been described to account for isolated CeH or combined pituitary hormone defects (CPHDs) with variable clinical characteristics and degrees of severity. The recently identified candidate gene IGSF1 appears frequently involved. This review provides an updated illustration of the different genetic defects accounting for CeH.

Familial Central Hypothyroidism Caused by a Novel IGSF1 Gene Mutation

BACKGROUND

Congenital hypothyroidism of central origin (CH-C) is a rare disease in which thyroid hormone deficiency is caused by insufficient thyrotropin stimulation of a normal thyroid gland. A recently described syndrome of isolated CH-C and macroorchidism was attributed to loss-of-function mutations of the immunoglobulin superfamily, member 1 gene (IGSF1).

PATIENTS AND METHODS

CH-C was diagnosed in three siblings. The TRH, TRHR, and TSHB genes were sequenced followed by whole-exome sequencing in the proband. A mutation identified in IGSF1 was analyzed by direct PCR sequencing in family members. The effects of the mutation were assessed by in vitro studies in HEK293 cells.

RESULTS

The index case was negative for mutations in TRH, TRHR, and TSHB. Whole-exome sequencing revealed a novel insertion mutation in IGSF1, c.2284_2285insA, p.R762QfsX7, which was confirmed by direct PCR sequencing and was identified in six additional family members. The mutation introduces a frame-shift and premature stop codon in the seventh Ig loop, thereby truncating IGSF1. In vitro studies revealed that the mutated IGSF1-R762QfsX7 migrates as a doublet at ∼28 kDa, which is far smaller than the wild type protein (130-140 kDa). Both bands were endonuclease H sensitive, indicating immature glycosylation and failure of the protein to traffic out of the endoplasmic reticulum to the plasma membrane. Further phenotypic findings in the family included macroorchidism and infertility in the uncle and mild neurological phenotypes in the affected males, such as hypotonia, delayed psychomotor development, clumsy behavior, and attention deficit disorder.

CONCLUSIONS

We identified a novel insertion mutation in the IGSF1 gene and further delineated the phenotype of the IGSF1-deficiency syndrome. Our findings indicate a possible association between an IGSF1 mutation and neurological phenotypes.

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.

A Japanese Family with Central Hypothyroidism Caused by a Novel IGSF1 Mutation

BACKGROUND

Hemizygous mutations in the immunoglobulin superfamily member 1 (IGSF1) gene have been demonstrated to cause congenital central hypothyroidism in males. This study reports a family with a novel mutation in the IGSF1 gene located on the long arm of the X chromosome.

PATIENT FINDINGS

A two-month-old boy was diagnosed with central hypothyroidism because of prolonged jaundice. A thyrotropin-releasing hormone (TRH) stimulation test indicated dysfunction in both the hypothalamus and the pituitary gland, and prompted the IGSF1 gene to be analyzed. The patient had a novel nonsense variant, c.2713C>T (p.Q905X), in exon 14 of the IGSF1 gene. Studies of the family revealed that the patient's sister and mother were heterozygous carriers of the IGSF1 mutation. The patient's maternal uncle carried the same mutation as the proband but had no overt symptoms. The mother and uncle started levothyroxine supplementation because of subclinical hypothyroidism.

SUMMARY

A novel mutation (c.2713C>T, p.Q905X) of the IGSF1 gene was identified that causes congenital central hypothyroidism in a Japanese family. The findings further expand the clinical heterogeneity of this entity.

Mutations in TBL1X Are Associated With Central Hypothyroidism

CONTEXT

Isolated congenital central hypothyroidism (CeH) can result from mutations in TRHR, TSHB, and IGSF1, but its etiology often remains unexplained. We identified a missense mutation in the transducin β-like protein 1, X-linked (TBL1X) gene in three relatives diagnosed with isolated CeH. TBL1X is part of the thyroid hormone receptor-corepressor complex.

OBJECTIVE

The objectives of the study were the identification of TBL1X mutations in patients with unexplained isolated CeH, Sanger sequencing of relatives of affected individuals, and clinical and biochemical characterization; in vitro investigation of functional consequences of mutations; and mRNA expression in, and immunostaining of, human hypothalami and pituitary glands.

DESIGN

This was an observational study.

SETTING

The study was conducted at university medical centers.

PATIENTS

Nineteen individuals with and seven without a mutation participated in the study.

MAIN OUTCOME MEASURES

Outcome measures included sequencing results, clinical and biochemical characteristics of mutation carriers, and results of in vitro functional and expression studies.

RESULTS

Sanger sequencing yielded five additional mutations. All patients (n = 8; six males) were previously diagnosed with CeH (free T₄ [FT4] concentration below the reference interval, normal thyrotropin). Eleven relatives (two males) also carried mutations. One female had CeH, whereas 10 others had low-normal FT4 concentrations. As a group, adult mutation carriers had 20%-25% lower FT4 concentrations than controls. Twelve of 19 evaluated carriers had hearing loss. Mutations are located in the highly conserved WD40-repeat domain of the protein, influencing its expression and thermal stability. TBL1X mRNA and protein are expressed in the human hypothalamus and pituitary.

CONCLUSIONS

TBL1X mutations are associated with CeH and hearing loss. FT4 concentrations in mutation carriers vary from low-normal to values compatible with CeH.

Identification of an IGSF1-specific deletion in a five-generation pedigree with X-linked Central Hypothyroidism without macroorchidism

OBJECTIVES

IGSF1 deficiency syndrome (IDS) is a recently described X-linked congenital central hypothyroidism disorder characterized by loss-of-function mutations in the immunoglobulin superfamily member 1 (IGSF1) gene. The phenotypic spectrum and intrafamilial variability associated with IDS remain unclear due to a paucity of large, well-characterized pedigrees. Here, we present phenotypic analysis and molecular characterization of a five-generation pedigree with IGSF1 deficiency containing 10 affected males.

PATIENTS AND METHODS

Pituitary function was assessed in all available family members (n = 8 affected males and n = 5 carrier females). Molecular characterization of the family was performed by Sanger sequencing of PCR products amplified from the IGSF1 locus and by array comparative genomic hybridization.

RESULTS

A 42-kb IGSF1 deletion spanning the entire coding sequence was identified in all affected males. TSH deficiency, although subclinical in one case, was identified in all affected males (n = 8). PRL and GH deficiency were also present in 5 of 6 and 4 of 8 affected males, respectively. In contrast to previous reports, macroorchidism was not detected in any of the four affected males who were examined for this feature. Only 1 of 5 carrier females had pituitary dysfunction (TSH and GH deficiency).

CONCLUSION

Individuals with identical IGSF1 deletions can exhibit variable pituitary hormone deficiencies, of which overt TSH deficiency is the most consistent feature. We also show that macroorchidism is not obligatory in males with IDS. Mutations of IGSF1 should therefore be considered in males with isolated hypopituitarism that includes TSH deficiency.

Combined Growth Hormone and Thyroid-Stimulating Hormone Deficiency in a Japanese Patient with a Novel Frameshift Mutation in IGSF1

BACKGROUND

Recent reports have indicated that loss-of-function mutations in the immunoglobulin superfamily member 1 gene (IGSF1, OMIM 300888) cause congenital central hypothyroidism with macroorchidism.

METHODS

We conducted a next-generation sequencing-based comprehensive mutation screening for pituitary hormone deficiencies to elucidate molecular mechanisms other than anatomical abnormalities of the pituitary that might be responsible for multiple anterior hormone deficiency in a male patient who originally visited our institute complaining of short stature. He was born large for gestational age (4,370 g, +3.0 SD) after an obstructed labour. Endocrinological evaluation revealed growth hormone and thyroid-stimulating hormone deficiency. Magnetic resonance imaging showed a discontinuity of the pituitary stalk with an ectopic posterior lobe and a hypoplastic anterior lobe, likely explaining multiple anterior pituitary hormone deficiency.

RESULT

We identified a novel hemizygous IGSF1 mutation (c.1137_1138delCA, p.Asn380Glnfs*6) in the patient. In reviewing the literature, we noticed that all reported Japanese male IGSF1 mutation carriers were born larger than mean standards for gestational age (mean birth weight SD score of +2.0, 95% confidence interval 1.0-3.0).

CONCLUSION

This case suggests that more attention should be paid to intrauterine growth and birth history when patients are suspected of having an IGSF1 mutation.

Mild deficits in attentional control in patients with the IGSF1 deficiency syndrome

OBJECTIVE

Male patients with the X-linked IGSF1 deficiency syndrome are characterized by central hypothyroidism, delayed pubertal testosterone rise, adult macroorchidism, variable prolactin deficiency and occasionally transient partial growth hormone deficiency. Thyroid hormone plays a vital role in brain development and functioning, and while most patients receive adequate replacement therapy starting shortly after birth, it is unknown whether this syndrome is accompanied by long-term impaired cognitive functioning. We therefore assessed cognitive functioning in male patients with IGSF1 deficiency.

METHODS

Fifteen adult male patients with IGSF1 deficiency participated in neuropsychological assessment of executive functioning and memory, and completed validated questionnaires on health-related quality of life (HRQoL), mood and fatigue. Results were compared to data from previous studies by our department: 54 healthy controls (76 for the attention task) for the test battery and 191 healthy controls for the questionnaires.

RESULTS

All patients had central hypothyroidism, and twelve were treated with levothyroxine. Patients performed worse than controls in tasks that required attentional control (Trail Making Test, Letter-Digit Substitution Test, and Sustained Attention to Response Task) (all P < 0·001). Memory was unaffected. In addition, patients reported more mental fatigue and reduction of activity (Multidimensional Fatigue Inventory) (both P < 0·01), while HRQoL and mood reports were not different from controls. Age at the start of replacement therapy and current thyroxine levels were not related to outcome.

CONCLUSIONS

Adult male patients with IGSF1 deficiency exhibit mild deficits in attentional control on formal testing. This finding was not related to the age at start of replacement therapy, or current levothyroxine treatment.

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.

MECHANISMS IN ENDOCRINOLOGY: Novel genetic causes of short stature

The fast technological development, particularly single nucleotide polymorphism array, array-comparative genomic hybridization, and whole exome sequencing, has led to the discovery of many novel genetic causes of growth failure. In this review we discuss a selection of these, according to a diagnostic classification centred on the epiphyseal growth plate. We successively discuss disorders in hormone signalling, paracrine factors, matrix molecules, intracellular pathways, and fundamental cellular processes, followed by chromosomal aberrations including copy number variants (CNVs) and imprinting disorders associated with short stature. Many novel causes of GH deficiency (GHD) as part of combined pituitary hormone deficiency have been uncovered. The most frequent genetic causes of isolated GHD are GH1 and GHRHR defects, but several novel causes have recently been found, such as GHSR, RNPC3, and IFT172 mutations. Besides well-defined causes of GH insensitivity (GHR, STAT5B, IGFALS, IGF1 defects), disorders of NFκB signalling, STAT3 and IGF2 have recently been discovered. Heterozygous IGF1R defects are a relatively frequent cause of prenatal and postnatal growth retardation. TRHA mutations cause a syndromic form of short stature with elevated T3/T4 ratio. Disorders of signalling of various paracrine factors (FGFs, BMPs, WNTs, PTHrP/IHH, and CNP/NPR2) or genetic defects affecting cartilage extracellular matrix usually cause disproportionate short stature. Heterozygous NPR2 or SHOX defects may be found in ∼3% of short children, and also rasopathies (e.g., Noonan syndrome) can be found in children without clear syndromic appearance. Numerous other syndromes associated with short stature are caused by genetic defects in fundamental cellular processes, chromosomal abnormalities, CNVs, and imprinting disorders.

IGSF1 Deficiency: Lessons From an Extensive Case Series and Recommendations for Clinical Management

CONTEXT

Mutations in the immunoglobulin superfamily, member 1 (IGSF1) gene cause the X-linked IGSF1 deficiency syndrome consisting of central hypothyroidism, delayed pubertal testosterone rise, adult macroorchidism, variable prolactin deficiency, and occasionally transient partial GH deficiency. Since our first reports, we discovered 20 new families with 18 new pathogenic IGSF1 mutations.

OBJECTIVE

We aimed to share data on the largest cohort of patients with IGSF1 deficiency to date and formulate recommendations for clinical management.

METHODS

We collected clinical and biochemical characteristics of 69 male patients (35 children, 34 adults) and 56 female IGSF1 mutation carriers (three children, 53 adults) from 30 unrelated families according to a standardized clinical protocol. At evaluation, boys were treated with levothyroxine in 89%, adult males in 44%, and females in 5% of cases.

RESULTS

Additional symptoms in male patients included small thyroid gland volume (74%), high birth weight (25%), and large head circumference (20%). In general, the timing of pubertal testicular growth was normal or even premature, in contrast to a late rise in T levels. Late adrenarche was observed in patients with prolactin deficiency, and adult dehydroepiandrosterone concentrations were decreased in 40%. Hypocortisolism was observed in 6 of 28 evaluated newborns, although cortisol concentrations were normal later. Waist circumference of male patients was increased in 60%, but blood lipids were normal. Female carriers showed low free T4 (FT4) and low-normal FT4 in 18% and 60%, respectively, delayed age at menarche in 31%, mild prolactin deficiency in 22%, increased waist circumference in 57%, and a negative correlation between FT4 concentrations and metabolic parameters.

CONCLUSION

IGSF1 deficiency represents the most common genetic cause of central hypothyroidism and is associated with multiple other characteristics. Based on these results, we provide recommendations for mutational analysis, endocrine work-up, and long-term care.

Delayed Adrenarche may be an Additional Feature of Immunoglobulin Super Family Member 1 Deficiency Syndrome

Immunoglobulin super family member 1 (IGSF1) deficiency syndrome is characterized by central hypothyroidism, delayed surge in testosterone during puberty, macro-orchidism, and in some cases, hypoprolactinemia and/or transient growth hormone (GH) deficiency. Our patient was a 19-year-old male adolescent who had been treated since the age of 9 years with GH and thyroxine for an idiopathic combined GH, thyroid-stimulating hormone (TSH), and prolactin (PRL) deficiency. His GH deficiency proved to be transient, but deficiencies of TSH and PRL persisted, and he had developed macro-orchidism since the end of puberty. Brain magnetic resonance imaging and PROP1 and POU1F1 sequencing were normal. A disharmonious puberty (delayed genital and pubic hair development, bone maturation, and pubertal growth spurt, despite normal testicular growth) was observed as well as a delayed adrenarche, as reflected by very low dehydroepiandrosterone sulfate and delayed pubarche. Direct sequencing of the IGSF1 gene revealed a novel hemizygous mutation, c.3127T>C, p.Cys1043Arg. Pathogenicity of the mutation was demonstrated in vitro. Male children with an idiopathic combined GH, PRL, and TSH deficiency, showing persistent central hypothyroidism but transient GH deficiency upon retesting at adult height, should be screened for mutations in the IGSF1 gene, especially when macro-orchidism and/or hypoprolactinemia are present. We suspect that delayed adrenarche, as a consequence of PRL deficiency, might be part of the clinical phenotype of patients with IGSF1 deficiency.

Pituitary Hormone Secretion Profiles in IGSF1 Deficiency Syndrome

BACKGROUND

Loss-of-function mutations in immunoglobulin superfamily member 1 (IGSF1) cause an X-linked syndrome of central hypothyroidism, macroorchidism, delayed pubertal testosterone rise, variable prolactin deficiency and variable partial GH deficiency in childhood. The clinical features and gene expression pattern suggest a pivotal role for IGSF1 in the pituitary, but detailed knowledge on pituitary hormone secretion in this syndrome is lacking. We therefore aimed to study the 24-hour pituitary hormone secretion in male patients with IGSF1 deficiency.

METHODS

We collected blood samples every 10 min for 24 h in eight adult male IGSF1-deficient patients and measured circulating TSH, prolactin and gonadotropins. Deconvolution, modified cosinor and approximate entropy analyses were applied to quantify secretion rates, diurnal rhythmicity and regularity of hormone release. Results were compared to healthy controls matched for age and body mass index.

RESULTS

Compared to healthy controls, IGSF1-deficient patients showed decreased pulsatile secretion of TSH with decreased disorderliness and reduced diurnal variation. Basal and pulsatile secretion of FSH was increased by over 200%, while LH secretion did not differ from healthy controls. We observed a bimodal distribution of prolactin secretion, i.e. severe deficiency in three and increased basal and total secretion in the other five patients.

CONCLUSION

The altered TSH secretion pattern is consistent with the previously hypothesized defect in thyrotropin-releasing hormone signaling in IGSF1 deficiency. However, the phenotype is more extensive and includes increased FSH secretion without altered LH secretion as well as either undetectable or increased prolactin secretion.

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.

Molecular insights into the aetiology of female reproductive ageing

As age at pubertal onset declines and age at first pregnancy increases, the mechanisms that regulate female reproductive lifespan become increasingly relevant to population health. The timing of menarche and menopause can have profound effects not only on fertility but also on the risk of diseases such as type 2 diabetes mellitus, cardiovascular disease and breast cancer. Genetic studies have identified dozens of highly penetrant rare mutations associated with reproductive disorders, and also ∼175 common genetic variants associated with the timing of puberty or menopause. These findings, alongside other functional studies, have highlighted a diverse range of mechanisms involved in reproductive ageing, implicating core biological processes such as cell cycle regulation and energy homeostasis. The aim of this article is to review the contribution of such genetic findings to our understanding of the molecular regulation of reproductive timing, as well as the biological basis of the epidemiological links between reproductive ageing and disease risk.

Spatial and temporal expression of immunoglobulin superfamily member 1 in the rat

Loss-of-function mutations in the immunoglobulin superfamily member 1 (IGSF1) gene cause an X-linked syndrome of central hypothyroidism, macroorchidism, variable prolactin and GH deficiency, delayed pubertal testosterone rise, and obesity. To understand the pathophysiology of this syndrome, knowledge on IGSF1's place in normal development is imperative. Therefore, we investigated spatial and temporal protein and mRNA expression of IGSF1 in rats using immunohistochemistry, real-time quantitative PCR (qPCR), and in situ hybridization. We observed high levels of IGSF1 expression in the brain, specifically the embryonic and adult choroid plexus and hypothalamus (principally in glial cells), and in the pituitary gland (PIT1-lineage of GH, TSH, and PRL-producing cells). IGSF1 is also expressed in the embryonic and adult zona glomerulosa of the adrenal gland, islets of Langerhans of the pancreas, and costameres of the heart and skeletal muscle. IGSF1 is highly expressed in fetal liver, but is absent shortly after birth. In the adult testis, IGSF1 is present in Sertoli cells (epithelial stages XIII-VI), and elongating spermatids (stages X-XII). Specificity of protein expression was corroborated with Igsf1 mRNA expression in all tissues. The expression patterns of IGSF1 in the pituitary gland and testis are consistent with the pituitary hormone deficiencies and macroorchidism observed in patients with IGSF1 deficiency. The expression in the brain, adrenal gland, pancreas, liver, and muscle suggest IGSF1's function in endocrine physiology might be more extensive than previously considered.

Rare coding variants and X-linked loci associated with age at menarche

More than 100 loci have been identified for age at menarche by genome-wide association studies; however, collectively these explain only ∼3% of the trait variance. Here we test two overlooked sources of variation in 192,974 European ancestry women: low-frequency protein-coding variants and X-chromosome variants. Five missense/nonsense variants (in ALMS1/LAMB2/TNRC6A/TACR3/PRKAG1) are associated with age at menarche (minor allele frequencies 0.08-4.6%; effect sizes 0.08-1.25 years per allele; P<5 × 10(-8)). In addition, we identify common X-chromosome loci at IGSF1 (rs762080, P=9.4 × 10(-13)) and FAAH2 (rs5914101, P=4.9 × 10(-10)). Highlighted genes implicate cellular energy homeostasis, post-transcriptional gene silencing and fatty-acid amide signalling. A frequently reported mutation in TACR3 for idiopathic hypogonatrophic hypogonadism (p.W275X) is associated with 1.25-year-later menarche (P=2.8 × 10(-11)), illustrating the utility of population studies to estimate the penetrance of reportedly pathogenic mutations. Collectively, these novel variants explain ∼0.5% variance, indicating that these overlooked sources of variation do not substantially explain the 'missing heritability' of this complex trait.