Central Hypothyroidism Due to a TRHR Mutation Causing Impaired Ligand Affinity and Transactivation of Gq

Normal intellectual ability and hyperprolactinemia as unique clinical manifestations of congenital hypothyroidism: A case report and review of hypotheses

Congenital hypothyroidism is the deficiency of thyroid hormone in infants and hyperprolactinemia is frequently observed. Previously reported cases typically involve intellectual disability, highlighting this particular unique case report to the first reported patient demonstrating normal intellectual ability despite experiencing growth and gonad dysfunction. This study aims to present a case and review medical hypotheses related to the patient's condition. A 19-year-old female presented with a chief complaint of irregular menstruation for up to 40 days or not occurring at all. The patient experienced the first menstruation at the age of 16 years old. The patient's height was 133 cm, body weight 40 kg, and body mass index 22.61 kg/m2; other family members were normal. Physical examination showed no abnormalities, and laboratory examination showed suppressed serum free T4 (FT4) level (6.41 pmol/L), elevated thyroid stimulating hormone (TSH) level (333.700 µIU/mL), and elevated prolactin hormone level (32.03 ng/mL). Ultrasound of the thyroid gland found hypoplasia of the left and right thyroid glands. The patient was a college student enrolled in a public national university and had never complained about academic performance throughout the patient's education. The patient was diagnosed with congenital hypothyroidism and hyperprolactinemia. The patient was administered up to 100 µg daily of oral levothyroxine, which improved the patient's menstrual cycles. The patient's delayed diagnosis may be attributed to central congenital hypothyroidism being underdiagnosed. We hypothesized that thyroid-releasing hormone receptor (TRHR) gene mutation might contribute to the underlying cause of hyperprolactinemia and normal intellectual ability of the patient. Further study on the significance of TRHR gene mutations in congenital hypothyroidism is required to improve diagnosis and treatment.

Genetic Basis of Congenital Central Hypothyroidism in Children: Expanding the Mutational Spectrum of POU1F1 and ATP6V0A4

Objective

Congenital central hypothyroidism (CCH) is a rare disorder poorly described in childhood and adolescence. The current knowledge on the genetic bases of CCH is scarce. The purpose of this study was to analyze the clinical characteristics and molecular genetic basis of CCH in children.

Methods

We conducted a thorough evaluation of the clinical features in children diagnosed with CCH. Genomic DNA was extracted from peripheral blood of both children and their parents, and chromosomal microarray analysis and whole-exome sequencing were performed. Candidates for single nucleotide variants were validated using Sanger sequencing and were classified according to the American College of Medical Genetics and Genomics (ACMG) and the Association for Molecular Pathology (AMP) guidelines.

Results

Two cases with likely pathogenic variants were detected by whole-exome sequencing. Individual 1 carried a novel homozygous ATP6V0A4 c.1418C>T (p.Ser473Phe) variant and a novel heterozygous POU1F1 c.416G>A. (p.Arg139Gln) variant. Individual 2 had a novel homozygous POU1F1 c.212C>T (p.Ala71Val) variant. The chromosomal microarray detected the presence of a 24 Mb heterozygous deletion (LOH: loss of heterozygosity) in the p12.1p13.13 region of chromosome 2 in individual 3, and the copy number variant was unknown of clinical significance.

Conclusion

Our study employed chromosomal microarray and whole-exome sequencing to investigate central hypothyroidism in seven children, leading to the detection of genetic anomalies in three individuals. The identification of novel variants has contributed to the expanded genetic spectrum of POU1F1 and ATP6V0A4 associated with pediatric central hypothyroidism.

The Genetic Landscape of Children Born Small for Gestational Age with Persistent Short Stature

INTRODUCTION

Among children born small for gestational age, 10-15% fail to catch up and remain short (SGA-SS). The underlying mechanisms are mostly unknown. We aimed to decipher genetic aetiologies of SGA-SS within a large single-centre cohort.

METHODS

Out of 820 patients treated with growth hormone (GH), 256 were classified as SGA-SS (birth length and/or birth weight <-2 SD for gestational age and life-minimum height <-2.5 SD). Those with the DNA triplet available (child and both parents) were included in the study (176/256). Targeted testing (karyotype/FISH/MLPA/specific Sanger sequencing) was performed if a specific genetic disorder was clinically suggestive. All remaining patients underwent MS-MLPA to identify Silver-Russell syndrome, and those with unknown genetic aetiology were subsequently examined using whole-exome sequencing or targeted panel of 398 growth-related genes. Genetic variants were classified using ACMG guidelines.

RESULTS

The genetic aetiology was elucidated in 74/176 (42%) children. Of these, 12/74 (16%) had pathogenic or likely pathogenic (P/LP) gene variants affecting pituitary development (LHX4, OTX2, PROKR2, PTCH1, POU1F1), the GH-IGF-1 or IGF-2 axis (GHSR, IGFALS, IGF1R, STAT3, HMGA2), 2/74 (3%) the thyroid axis (TRHR, THRA), 17/74 (23%) the cartilaginous matrix (ACAN, various collagens, FLNB, MATN3), and 7/74 (9%) the paracrine chondrocyte regulation (FGFR3, FGFR2, NPR2). In 12/74 (16%), we revealed P/LP affecting fundamental intracellular/intranuclear processes (CDC42, KMT2D, LMNA, NSD1, PTPN11, SRCAP, SON, SOS1, SOX9, TLK2). SHOX deficiency was found in 7/74 (9%), Silver-Russell syndrome in 12/74 (16%) (11p15, UPD7), and miscellaneous chromosomal aberrations in 5/74 (7%) children.

CONCLUSIONS

The high diagnostic yield sheds a new light on the genetic landscape of SGA-SS, with a central role for the growth plate with substantial contributions from the GH-IGF-1 and thyroid axes and intracellular regulation and signalling.

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.

Biochemical and physiological insights into TRH receptor-mediated signaling

Thyrotropin-releasing hormone (TRH) is an important endocrine agent that regulates the function of cells in the anterior pituitary and the central and peripheral nervous systems. By controlling the synthesis and release of thyroid hormones, TRH affects many physiological functions, including energy homeostasis. This hormone exerts its effects through G protein-coupled TRH receptors, which signal primarily through G_q/11 but may also utilize other G protein classes under certain conditions. Because of the potential therapeutic benefit, considerable attention has been devoted to the synthesis of new TRH analogs that may have some advantageous properties compared with TRH. In this context, it may be interesting to consider the phenomenon of biased agonism and signaling at the TRH receptor. This possibility is supported by some recent findings. Although knowledge about the mechanisms of TRH receptor-mediated signaling has increased steadily over the past decades, there are still many unanswered questions, particularly about the molecular details of post-receptor signaling. In this review, we summarize what has been learned to date about TRH receptor-mediated signaling, including some previously undiscussed information, and point to future directions in TRH research that may offer new insights into the molecular mechanisms of TRH receptor-triggered actions and possible ways to modulate TRH receptor-mediated signaling.

[Clinical guideline of «congenital hypothyroidism»]

Congenital hypothyroidism is an important issue of pediatric endocrinology at which timely diagnosis and treatment can prevent the development of severe cases of the disease. The developed clinical guidelines are a working tool for a practicing physician. The target audience is pediatric endocrinologists and pediatricians. They briefly and logically set out the main definition of the disease, epidemiology, classification, methods of diagnosis and treatment, based on the principles of -evidence-based medicine.

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.

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.

A Gq Biased Small Molecule Active at the TSH Receptor

G protein coupled receptors (GPCRs) can lead to G protein and non-G protein initiated signals. By virtue of its structural property, the TSH receptor (TSHR) has a unique ability to engage different G proteins making it highly amenable to selective signaling. In this study, we describe the identification and characterization of a novel small molecule agonist to the TSHR which induces primary engagement with G_αq/11. To identify allosteric modulators inducing selective signaling of the TSHR we used a transcriptional-based luciferase assay system with CHO-TSHR cells stably expressing response elements (CRE, NFAT, SRF, or SRE) that were capable of measuring signals emanating from the coupling of G_αs , G_αq/11, G_βγ, and G_α12/13, respectively. Using this system, TSH activated G_αs , G_αq/11, and G_α12/13 but not G_βγ. On screening a library of 50K molecules at 0.1,1.0 and 10 μM, we identified a novel G_q/11 agonist (named MSq1) which activated G_q/11 mediated NFAT-luciferase >4 fold above baseline and had an EC₅₀= 8.3 × 10^-9 M with only minor induction of G_αs and cAMP. Furthermore, MSq1 is chemically and structurally distinct from any of the previously reported TSHR agonist molecules. Docking studies using a TSHR transmembrane domain (TMD) model indicated that MSq1 had contact points on helices H1, H2, H3, and H7 in the hydrophobic pocket of the TMD and also with the extracellular loops. On co-treatment with TSH, MSq1 suppressed TSH-induced proliferation of thyrocytes in a dose-dependent manner but lacked the intrinsic ability to influence basal thyrocyte proliferation. This unexpected inhibitory property of MSq1 could be blocked in the presence of a PKC inhibitor resulting in derepressing TSH induced protein kinase A (PKA) signals and resulting in the induction of proliferation. Thus, the inhibitory effect of MSq1 on proliferation resided in its capacity to overtly activate protein kinase C (PKC) which in turn suppressed the proliferative signal induced by activation of the predomiant cAMP-PKA pathway of the TSHR. Treatment of rat thyroid cells (FRTL5) with MSq1 did not show any upregulation of gene expression of the key thyroid specific markers such as thyroglobulin(Tg), thyroid peroxidase (Tpo), sodium iodide symporter (Nis), and the TSH receptor (Tshr) further suggesting lack of involvement of MSq1 and G_αq/11 activation with cellular differentation. In summary, we identified and characterized a novel G_αq/11 agonist molecule acting at the TSHR and which showed a marked anti-proliferative ability. Hence, Gq biased activation of the TSHR is capable of ameliorating the proliferative signals from its orthosteric ligand and may offer a therapeutic option for thyroid growth modulation.

Central hypothyroidism

Central hypothyroidism is a rare cause of hypothyroidism, consequence of various disorders affecting pituitary (secondary) or hypothalamus (tertiary hypothyroidism). Difficulties in the diagnosis and management of patients are due to the nontypical clinical picture, frequent combination with impaired function of other pituitary hormones, difficulties in laboratory assessment in high TSH levels or low - normal T4 free levels. Diagnosis is based on a confirmed decrease in the level of free T4 with a low or normal level of TSH. The standard treatment for hypothyroidism of any etiology remains monotherapy with levothyroxine, which allows to restore the euthyroid state in most patients. The criterion for the effectiveness of therapy is to maintain the level of T4 free in the upper half of the reference norm interval. The article presents a modern understanding of epidemiology, pathogenesis and strategies for managing patients with central hypothyroidism.

High Prevalence of Growth Plate Gene Variants in Children With Familial Short Stature Treated With GH

CONTEXT

Familial short stature (FSS) is a term describing a growth disorder that is vertically transmitted. Milder forms may result from the combined effect of multiple genes; more severe short stature is suggestive of a monogenic condition. The etiology of most FSS cases has not been thoroughly elucidated to date.

OBJECTIVES

To identify the genetic etiology of severe FSS in children treated with GH because of the diagnosis of small for gestational age or GH deficiency (SGA/GHD).

DESIGN, SETTINGS, AND PATIENTS

Of 736 children treated with GH because of GHD/SGA, 33 with severe FSS (life-minimum height -2.5 SD or less in both the patient and shorter parent) were included in the study. The genetic etiology was known in 5 of 33 children prior to the study [ACAN (in 2], NF1, PTPN11, and SOS1). In the remaining 28 of 33, whole-exome sequencing was performed. The results were evaluated using American College of Medical Genetics and Genomics standards and guidelines.

RESULTS

In 30 of 33 children (90%), we found at least one variant with potential clinical significance in genes known to affect growth. A genetic cause was elucidated in 17 of 33 (52%). Of these children, variants in growth plate-related genes were found in 9 of 17 [COL2A1, COL11A1, and ACAN (all in 2), FLNB, FGFR3, and IGF1R], and IGF-associated proteins were affected in 2 of 17 (IGFALS and HMGA2). In the remaining 6 of 17, the discovered genetic mechanisms were miscellaneous (TRHR, MBTPS2, GHSR, NF1, PTPN11, and SOS1).

CONCLUSIONS

Single-gene variants are frequent among families with severe FSS, with variants affecting the growth plate being the most prevalent.

Recent advances in research on isolated congenital central hypothyroidism

Congenital central hypothyroidism (C-CH) is caused by defects in the secretion of thyrotropin-releasing hormone (TRH) and/or TSH, leading to an impairment in the release of hormones from the thyroid. The causes of C-CH include congenital anomalies of the hypothalamic-pituitary regions and several genetic defects. In terms of endocrinology, C-CH is divided into two categories: (1) accompanied by another pituitary hormone deficiency and called combined pituitary hormone deficiency, and (2) isolated C-CH, showing mainly TSH deficiency. For isolated C-CH, a mutation in the TSH gene (TSHB) encoding the β-subunit of the protein was first found in 1990 by Japanese researchers, and thereafter several mutations in TSHB have been reported. Mutations in the thyrotropin-releasing hormone receptor gene (TRHR), as well as genetic defects in immunoglobulin superfamily 1 (IGSF1), have also been identified. It was recently found that isolated C-CH is caused by mutations in transducin β-like 1 X-linked and insulin receptor substrate 4. It is noted that all patients with TSHB deficiency and some with IGSF1 deficiency show severe hypothyroidism soon after birth. Among the causes of C-CH, high frequency of mutations in IGSF1 is the most prevalent. This review focuses on recent findings on isolated C-CH.

DIAGNOSIS OF ENDOCRINE DISEASE: Congenital hypothyroidism: update and perspectives

Congenital hypothyroidism (CH) may be primary, due to a defect affecting the thyroid gland itself, or central, due to impaired thyroid-stimulating hormone (TSH)-mediated stimulation of the thyroid gland as a result of hypothalamic or pituitary pathology. Primary CH is the most common neonatal endocrine disorder, traditionally subdivided into thyroid dysgenesis (TD), referring to a spectrum of thyroid developmental abnormalities, and dyshormonogenesis, where a defective molecular pathway for thyroid hormonogenesis results in failure of hormone production by a structurally intact gland. Delayed treatment of neonatal hypothyroidism may result in profound neurodevelopmental delay; therefore, CH is screened for in developed countries to facilitate prompt diagnosis. Central congenital hypothyroidism (CCH) is a rarer entity which may occur in isolation, or (more frequently) in association with additional pituitary hormone deficits. CCH is most commonly defined biochemically by failure of appropriate TSH elevation despite subnormal thyroid hormone levels and will therefore evade diagnosis in primary, TSH-based CH-screening programmes. This review will discuss recent genetic aetiological advances in CH and summarize epidemiological data and clinical diagnostic challenges, focussing on primary CH and isolated CCH.

Central Hypothyroidism and Novel Clinical Phenotypes in Hemizygous Truncation of TBL1X

Transducin β-like 1 X-linked (TBL1X) gene encodes a subunit of the nuclear corepressor-silencing mediator for retinoid and thyroid hormone receptor complex (NCoR-SMRT) involved in repression of thyroid hormone action in the pituitary and hypothalamus. TBL1X defects were recently associated with central hypothyroidism and hearing loss. The current study aims to describe the clinical and genetic characterization of a male diagnosed with central hypothyroidism through thyroid hormone profiling, TRH test, brain MRI, audiometry, and psychological evaluation. Next-generation sequencing of known genes involved in thyroid disorders was implemented. The 6-year-old boy was diagnosed with central hypothyroidism [free T4: 10.42 pmol/L (normal: 12 to 22 pmol/L); TSH: 1.57 mIU/L (normal: 0.7 to 5.7 mIU/L)], with a mildly reduced TSH response to TRH. He was further diagnosed with attention-deficit/hyperactivity disorder (ADHD) at 7 years, alternating episodes of encopresis and constipation, and frequent headaches. MRI showed a normal pituitary but detected a Chiari malformation type I (CMI). At 10 years, audiometry identified poor hearing threshold at high frequencies. Sequencing revealed a nonsense hemizygous mutation in TBL1X [c.1015C>T; p.(Arg339Ter)] largely truncating its WD-40 repeat domain involved in nuclear protein-protein interactions. In conclusion, to our knowledge, we identified the first severely truncating TBL1X mutation in a patient with central hypothyroidism, hypoacusia, and novel clinical features like ADHD, gastrointestinal dysmotility, and CMI. Given the relevance of TBL1X and NCoR-SMRT for the regulation of transcriptional programs at different tissues (pituitary, cochlea, brain, fossa posterior, and cerebellum), severe mutations in TBL1X may lead to a distinct syndrome with a phenotypic spectrum wider than previously reported.

2018 European Thyroid Association (ETA) Guidelines on the Diagnosis and Management of Central Hypothyroidism

OBJECTIVES

Central hypothyroidism (CeH) is a rare form of hypothyroidism characterized by insufficient thyroid stimulation due to disturbed pituitary and/or hypothalamic functioning. Due to its origin and the whole clinical context, CeH represents a challenging condition in clinical practice as it is characterized by suboptimal accuracy of clinical and biochemical parameters for diagnosis and management. Since no expert consensus or guidance for this condition is currently available, a task force of experts received the commitment from the European Thyroid Association (ETA) to prepare this document based on the principles of clinical evidence.

STUDY DESIGN

The task force started to work in February 2017 and after a careful selection of appropriate references (cohort studies, case reports, expert opinions), a preliminary presentation and live discussion during the 2017 ETA meeting, and several revision rounds, has prepared a list of recommendations to support the diagnosis and management of patients with CeH.

RESULTS

Due to the particular challenges of this rare condition in the different ages, the target users of this guidance are pediatric and adult endocrinologists. Experts agreed on the need to recognize and treat overt CeH at all ages, whereas treatment of milder forms may be dispensable in the elderly (> 75 years).

CONCLUSIONS

Despite the lack of randomized controlled clinical trials, the experts provide 34 recommendations supported by variable levels of strength that should improve the quality of life of the affected patients and reduce the metabolic and hormonal consequences of inadequate management.

Regulatory aspects of the human hypothalamus-pituitary-thyroid axis

Thyroid hormones are essential for growth, differentiation and metabolism during prenatal and postnatal life. The hypothalamus-pituitary-thyroid (HPT)-axis is optimized for these actions. Knowledge of this hormonal axis is derived from decades of experiments in animals and man, and more recently from spontaneous mutations in man and constructed mutations in mice. This review examines the HPT-axis in relation to 24 h TSH profiles in men in various physiological and pathophysiological conditions, including obesity, age, longevity, and primary as well as central hypothyroidism. Hormone rhythms can be analyzed by quantitative methods, e.g. operator-independent deconvolution, approximate entropy and fitting the 24-h component by Cosinor analysis or related procedures. These approaches have identified some of the regulatory components in (patho)physiological conditions.