A Novel Thyrotropin-Releasing Hormone Receptor Missense Mutation (P81R) in Central Congenital Hypothyroidism

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.

Identification of genetic variants and phenotypic characterization of a large cohort of patients with congenital hypopituitarism and related disorders

PURPOSE

Congenital hypopituitarism (CH) disorders are phenotypically variable. Variants in multiple genes are associated with these disorders, with variable penetrance and inheritance.

METHODS

We screened a large cohort (N = 1765) of patients with or at risk of CH using Sanger sequencing, selected according to phenotype, and conducted next-generation sequencing (NGS) in 51 families within our cohort. We report the clinical, hormonal, and neuroradiological phenotypes of patients with variants in known genes associated with CH.

RESULTS

We identified variants in 178 patients: GH1/GHRHR (51 patients of 414 screened), PROP1 (17 of 253), POU1F1 (15 of 139), SOX2 (13 of 59), GLI2 (7 of 106), LHX3/LHX4 (8 of 110), HESX1 (8 of 724), SOX3 (9 of 354), OTX2 (5 of 59), SHH (2 of 64), and TCF7L1, KAL1, FGFR1, and FGF8 (2 of 585, respectively). NGS identified 26 novel variants in 35 patients (from 24 families). Magnetic resonance imaging showed prevalent hypothalamo-pituitary abnormalities, present in all patients with PROP1, GLI2, SOX3, HESX1, OTX2, LHX3, and LHX4 variants. Normal hypothalamo-pituitary anatomy was reported in 24 of 121, predominantly those with GH1, GHRHR, POU1F1, and SOX2 variants.

CONCLUSION

We identified variants in 10% (178 of 1765) of our CH cohort. NGS has revolutionized variant identification, and careful phenotypic patient characterization has improved our understanding of CH. We have constructed a flow chart to guide genetic analysis in these patients, which will evolve upon novel gene discoveries.

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.

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.

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.

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.

Pilot Neonatal Screening Program for Central Congenital Hypothyroidism: Evidence of Significant Detection

BACKGROUND/AIM

Congenital hypothyroidism (CH) is a heterogeneous entity. Neonatal screening programs based on thyrotropin (TSH) determination allow primary CH diagnosis but miss central CH (CCH). CCH causes morbidity, alerts to other pituitary deficiencies, and is more prevalent than previously thought. We aimed at developing a pilot neonatal screening program for CCH detection.

PATIENTS AND METHODS

A prospective 2-year pilot neonatal screening study based on simultaneous dried blood specimen TSH and thyroxine (T4) measurements was implemented in term newborns aged 2-7 days. Those with T4 ≤4.5 µg/dL (-2.3 SDS) and TSH <10 mIU/L were recalled (suspicious of CCH) and underwent clinical and biochemical assessment performed by expert pediatric endocrinologists.

RESULTS

A total of 67,719 newborns were screened. Primary CH was confirmed in 24 (1: 2,821). Forty-four newborns with potential CCH were recalled (recall rate 0.07%) at a mean age of 12.6 ± 4.8 days. In this group, permanent CCH was confirmed in 3 (1: 22,573), starting L-T4 treatment at a mean age of 12.3 ± 6.6 days; 14 boys showed T4-binding globulin deficiency (1: 4,837); 24 had transient hypothyroxinemia (21 non-thyroidal illness and 3 healthy); and 3 died before the confirmation stage. According to initial free T4 measurements, CCH patients had moderate hypothyroidism.

CONCLUSIONS

Adding T4 to TSH measurements enabled the identification of CCH as a prevalent condition and contributed to improving the care of newborns with congenital hypopituitarism and recognizing other thyroidal disorders.

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.

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.

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

CONTEXT

Central congenital hypothyroidism (CCH) is an underdiagnosed disorder characterized by deficient production and bioactivity of thyroid-stimulating hormone (TSH) leading to low thyroid hormone synthesis. Thyrotropin-releasing hormone (TRH) receptor (TRHR) defects are rare recessive disorders usually associated with incidentally identified CCH and short stature in childhood.

OBJECTIVES

Clinical and genetic characterization of a consanguineous family of Roma origin with central hypothyroidism and identification of underlying molecular mechanisms.

DESIGN

All family members were phenotyped with thyroid hormone profiles, pituitary magnetic resonance imaging, TRH tests, and dynamic tests for other pituitary hormones. Candidate TRH, TRHR, TSHB, and IGSF1 genes were screened for mutations. A mutant TRHR was characterized in vitro and by molecular modeling.

RESULTS

A homozygous missense mutation in TRHR (c.392T > C; p.I131T) was identified in an 8-year-old boy with moderate hypothyroidism (TSH: 2.61 mIU/L, Normal: 0.27 to 4.2; free thyroxine: 9.52 pmol/L, Normal: 10.9 to 25.7) who was overweight (body mass index: 20.4 kg/m2, p91) but had normal stature (122 cm; -0.58 standard deviation). His mother, two brothers, and grandmother were heterozygous for the mutation with isolated hyperthyrotropinemia (TSH: 4.3 to 8 mIU/L). The I131T mutation, in TRHR intracellular loop 2, decreases TRH affinity and increases the half-maximal effective concentration for signaling. Modeling of TRHR-Gq complexes predicts that the mutation disrupts the interaction between receptor and a hydrophobic pocket formed by Gq.

CONCLUSIONS

A unique missense TRHR defect identified in a consanguineous family is associated with central hypothyroidism in homozygotes and hyperthyrotropinemia in heterozygotes, suggesting compensatory elevation of TSH with reduced biopotency. The I131T mutation decreases TRH binding and TRHR-Gq coupling and signaling.

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.

Advances in TRH signaling

The activity of the hypothalamus-pituitary-thyroid axis (HPT) is coordinated by hypophysiotropic thyrotropin releasing hormone (TRH) neurons present in the paraventricular nucleus of the hypothalamus. Hypophysiotropic TRH neurons act as energy sensors. TRH controls the synthesis and release of thyrotropin, which activates the synthesis and secretion of thyroid hormones; in target tissues, transporters and deiodinases control their local availability. Thyroid hormones regulate many functions, including energy homeostasis. This review discusses recent evidence that covers several aspects of TRH role in HPT axis regulation. Knowledge about the mechanisms of TRH signaling has steadily increased. New transcription factors engaged in TRH gene expression have been identified, and advances made on how they interact with signaling pathways and define the dynamics of TRH neurons response to acute and/or long-term influences. Albeit yet incomplete, the relationship of TRH neurons activity with positive energy balance has emerged. The importance of tanycytes as a central relay for the feedback control of the axis, as well as for HPT responses to alterations in energy balance, and other stimuli has been reinforced. Finally, some studies have started to shed light on the interference of prenatal and postnatal stress and nutrition on HPT axis programing, which have confirmed the axis susceptibility to early insults.

Minireview: Insights Into the Structural and Molecular Consequences of the TSH-β Mutation C105Vfs114X

Naturally occurring thyrotropin (TSH) mutations are rare, which is also the case for the homologous heterodimeric glycoprotein hormones (GPHs) follitropin (FSH), lutropin (LH), and choriogonadotropin (CG). Patients with TSH-inactivating mutations present with central congenital hypothyroidism. Here, we summarize insights into the most frequent loss-of-function β-subunit of TSH mutation C105Vfs114X, which is associated with isolated TSH deficiency. This review will address the following question. What is currently known on the molecular background of this TSH variant on a protein level? It has not yet been clarified how C105Vfs114X causes early symptoms in affected patients, which are comparably severe to those observed in newborns lacking any functional thyroid tissue (athyreosis). To better understand the mechanisms of this mutant, we have summarized published reports and complemented this information with a structural perspective on GPHs. By including the ancestral TSH receptor agonist thyrostimulin and pathogenic mutations reported for FSH, LH, and choriogonadotropin in the analysis, insightful structure function and evolutionary restrictions become apparent. However, comparisons of immunogenicity and bioactivity of different GPH variants is hindered by a lack of consensus for functional analysis and the diversity of used GPH assays. Accordingly, relevant gaps of knowledge concerning details of GPH mutation-related effects are identified and highlighted in this review. These issues are of general importance as several previous and recent studies point towards the high impact of GPH variants in differential signaling regulation at GPH receptors (GPHRs), both endogenously and under diseased conditions. Further improvement in this area is of decisive importance for the development of novel targeted therapies.