Prolonged and Severe Gestational Thyrotoxicosis Due to Enhanced hCG Sensitivity of a Mutant Thyrotropin Receptor

Mechanisms of thyrotropin receptor-mediated phenotype variability deciphered by gene mutations and M453T-knockin model

The clinical spectrum of thyrotropin receptor-mediated (TSHR-mediated) diseases varies from loss-of-function mutations causing congenital hypothyroidism to constitutively active mutations (CAMs) leading to nonautoimmune hyperthyroidism (NAH). Variation at the TSHR locus has also been associated with altered lipid and bone metabolism and autoimmune thyroid diseases. However, the extrathyroidal roles of TSHR and the mechanisms underlying phenotypic variability among TSHR-mediated diseases remain unclear. Here we identified and characterized TSHR variants and factors involved in phenotypic variability in different patient cohorts, the FinnGen database, and a mouse model. TSHR CAMs were found in all 16 patients with NAH, with 1 CAM in an unexpected location in the extracellular leucine-rich repeat domain (p.S237N) and another in the transmembrane domain (p.I640V) in 2 families with distinct hyperthyroid phenotypes. In addition, screening of the FinnGen database revealed rare functional variants as well as distinct common noncoding TSHR SNPs significantly associated with thyroid phenotypes, but there was no other significant association between TSHR variants and more than 2,000 nonthyroid disease endpoints. Finally, our TSHR M453T-knockin model revealed that the phenotype was dependent on the mutation's signaling properties and was ameliorated by increased iodine intake. In summary, our data show that TSHR-mediated disease risk can be modified by variants at the TSHR locus both inside and outside the coding region as well as by altered TSHR-signaling and dietary iodine, supporting the need for personalized treatment strategies.

Hyperthyroidism: aetiology, pathogenesis, diagnosis, management, complications, and prognosis

Hyperthyroidism is a common condition with a global prevalence of 0·2-1·3%. When clinical suspicion of hyperthyroidism arises, it should be confirmed by biochemical tests (eg, low TSH, high free thyroxine [FT4], or high free tri-iodothyonine [FT3]). If hyperthyroidism is confirmed by biochemical tests, a nosological diagnosis should be done to find out which disease is causing the hyperthyroidism. Helpful tools are TSH-receptor antibodies, thyroid peroxidase antibodies, thyroid ultrasonography, and scintigraphy. Hyperthyroidism is mostly caused by Graves' hyperthyroidism (70%) or toxic nodular goitre (16%). Hyperthyroidism can also be caused by subacute granulomatous thyroiditis (3%) and drugs (9%) such as amiodarone, tyrosine kinase inhibitors, and immune checkpoint inhibitors. Disease-specific recommendations are given. Currently, Graves' hyperthyroidism is preferably treated with antithyroid drugs. However, recurrence of hyperthyroidism after a 12-18 month course of antithyroid drugs occurs in approximately 50% of patients. Being younger than 40 years, having FT4 concentrations that are 40 pmol/L or higher, having TSH-binding inhibitory immunoglobulins that are higher than 6 U/L, and having a goitre size that is equivalent to or larger than WHO grade 2 before the start of treatment with antithyroid drugs increase risk of recurrence. Long-term treatment with antithyroid drugs (ie, 5-10 years of treatment) is feasible and associated with fewer recurrences (15%) than short-term treatment (ie, 12-18 months of treatment). Toxic nodular goitre is mostly treated with radioiodine (131I) or thyroidectomy and is rarely treated with radiofrequency ablation. Destructive thyrotoxicosis is usually mild and transient, requiring steroids only in severe cases. Specific attention is given to patients with hyperthyroidism who are pregnant, have COVID-19, or have other complications (eg, atrial fibrillation, thyrotoxic periodic paralysis, and thyroid storm). Hyperthyroidism is associated with increased mortality. Prognosis might be improved by rapid and sustained control of hyperthyroidism. Innovative new treatments are expected for Graves' disease, by targeting B cells or TSH receptors.

MANAGEMENT OF THYROTOXICOSIS AND PREGNANCY: Review of the current literature and an update of the care pathway

Pregnancy can be complicated by hyperthyroidism or thyrotoxicosis. Diagnosis is founded on an increase in free thyroid hormones and low TSH. The most frequent etiologies are Graves' disease, an autoimmune disease linked to stimulatory anti-TSH receptor antibodies, and non-autoimmune gestational hyperthyroidism linked to the TSH-like activity of the chorionic growth hormone (hCG). During pregnancy, thyrotoxicosis can entail maternal, obstetrical and fetal or neonatal complications. Graves' hyperthyroidism may be responsible for fetal and neonatal hyperthyroidism due to placental transfer of stimulatory anti-TSH receptor antibodies. During pregnancy, treatment of thyrotoxicosis must restore normal thyroid function in the mother without affecting fetal thyroid function. The recent reassessment of the prevalence of teratogenic effects in children of women treated with antithyroid drugs in the first weeks of gestation should orient the care pathway before and during pregnancy for women of child-bearing age with hyperthyroidism linked to Graves' disease.

Mutations in G Protein-Coupled Receptors: Mechanisms, Pathophysiology and Potential Therapeutic Approaches

There are approximately 800 annotated G protein-coupled receptor (GPCR) genes, making these membrane receptors members of the most abundant gene family in the human genome. Besides being involved in manifold physiologic functions and serving as important pharmacotherapeutic targets, mutations in 55 GPCR genes cause about 66 inherited monogenic diseases in humans. Alterations of nine GPCR genes are causatively involved in inherited digenic diseases. In addition to classic gain- and loss-of-function variants, other aspects, such as biased signaling, trans-signaling, ectopic expression, allele variants of GPCRs, pseudogenes, gene fusion, and gene dosage, contribute to the repertoire of GPCR dysfunctions. However, the spectrum of alterations and GPCR involvement is probably much larger because an additional 91 GPCR genes contain homozygous or hemizygous loss-of-function mutations in human individuals with currently unidentified phenotypes. This review highlights the complexity of genomic alteration of GPCR genes as well as their functional consequences and discusses derived therapeutic approaches. SIGNIFICANCE STATEMENT: With the advent of new transgenic and sequencing technologies, the number of monogenic diseases related to G protein-coupled receptor (GPCR) mutants has significantly increased, and our understanding of the functional impact of certain kinds of mutations has substantially improved. Besides the classical gain- and loss-of-function alterations, additional aspects, such as biased signaling, trans-signaling, ectopic expression, allele variants of GPCRs, uniparental disomy, pseudogenes, gene fusion, and gene dosage, need to be elaborated in light of GPCR dysfunctions and possible therapeutic strategies.

New variant (Val597Ile) in transmembrane region of the TSH receptor with human chorionic gonadotropin hypersensitivity in familial gestational hyperthyroidism

OBJECTIVES

Only two mutations at the lysine 183 amino acid in the extracellular N-terminal domain of human TSH receptor (hTSHR) have been associated with hypersensitivity to hCG and familial gestational hyperthyroidism.

DESIGN

Describe a new variant of the TSHR gene with hCG hypersensitivity found in two women of the same family diagnosed with gestational hyperthyroidism.

PATIENTS

A 38-year-old woman was seen during the first trimester of her second pregnancy for thyrotoxicosis with increased fT3 and fT4 concentrations and low TSH levels without anti-TSH receptor antibody. Thyrotoxicosis improved spontaneously during the 2nd trimester and persisted at the 3rd trimester. Similar clinical symptoms (weight loss, nausea, vomiting) were also reported during the first trimester of her first pregnancy and the first pregnancy of her mother.

RESULTS

DNA sequencing of the hTSHR gene of this woman and her mother identifies a heterozygous variant changing valine to isoleucine residue at codon 597 in the transmembrane domain (TMD) of this receptor. In vitro functional studies of this variant showed increased constitutive activity in regard to the basal level of cAMP and IP3 production and to the low cell-surface expression, while response to TSH was reduced compared to that of the wild-type receptor. The Val597Ile variant presented a dose-dependent increase in cAMP response to hGC and human luteinizing hormone (hLH). Simulation of the protein dynamics showed a high structural impact of the Val597Ile variant on helices 3 (TMH3) and 5 (TMH5) of the transmembrane domain participating to constitutive activity and hCG sensitivity.

CONCLUSION

We describe a new variant in the transmembrane region of the hTSHR gene with increased constitutive activity and hCG hypersensitivity in familial gestational hyperthyroidism.

Pitfalls in the assessment of gestational transient thyrotoxicosis

Gestational transient thyrotoxicosis (GTT) is associated with direct stimulation of the maternal thyroid gland by human chorionic gonadotropin (hCG). It is characterized by slightly higher thyroid hormone and lower thyroid-stimulating hormone (TSH) levels in early pregnancy and mild or no symptoms. While GTT must be distinguished from Graves' disease (GD), which is associated with maternal and fetal complications, treated GD and new-onset GD in pregnancy are occasionally challenging to distinguish. Evaluating serum hCG levels and TSH receptor antibody (TRAb) titers can help, but the results are not irrefutable due to pregnancy-related immunosuppression. Moreover, GTT can follow unusual clinical courses in relation to some pregnancy complications. Excessive hCG production can cause severe GTT symptoms in patients with hyperemesis gravidarum, trophoblastic disease, or multiple pregnancies. Thyrotoxicosis can emerge beyond the second trimester in patients with gestational diabetes mellitus and mirror syndrome, because of delayed elevations in the hCG levels. Detailed knowledge about GTT is necessary for correct diagnoses and its appropriate management. This review focuses on the diagnosis of GTT, and, particularly, its differentiation from GD, and unusual clinical conditions associated with GTT that require comprehensive management.

A CASE OF FAMILIAL NONAUTOIMMUNE HYPERTHYROIDISM DURING PREGNANCY

Objective

Familial nonautoimmune hyperthyroidism (FNAH) is a rare disease. To date there are few, if any, reports of pregnancies in women with FNAH. Our objective here is to present such a case.

Methods

Free thyroxine (free T4), free triiodothyronine (free T3), thyroid-stimulating hormone (TSH), and antibodies related to the thyroid were measured. Fetal thyroid function indicators including thyroid volume and ossification were checked using ultrasound. Thyroid-stimulating hormone receptor (TSHR) gene analyses were performed.

Results

The patient was a 30-year-old woman with no past medical history. She was introduced to our hospital in the fifth gestational week for pregnancy care because her family history revealed that her mother had nonautoimmune hyperthyroidism with a TSHR-activating germ-line mutation (Asn406Ser). The serum free T4 was 1.88 ng/dL (normal, 0.62 to 1.19 ng/dL), free T3 was 3.27 pg/mL (normal, 2.55 to 3.88 pg/mL), TSH was 0.02 μIU/mL (normal, 0.007 to 3.619 μIU/mL), and TSHR was negative which were considered to be consistent with mild primary hyperthyroidism. Serum free T4, free T3, and TSH concentrations were monitored every 4 to 6 weeks with a peak free T4 of 2.23 ng/dL noted at gestational week 9. The patient had no signs related to hyperthyroidism throughout pregnancy. The patient delivered a 3,518 g girl at 40 weeks of gestation. Genetic analysis of her TSHR gene showed heterozygous Asn406Ser mutation. The offspring did not show any signs of prenatal hyperthyroidism, and thyroid function at day 6 after delivery revealed a free T4 of 2.41 ng/dL (normal, 1.83 to 2.91 ng/dL) and a TSH of 3.55 μIU/mL (normal, 0.51 to 4.57 μIU/mL).

Conclusion

Women with FNAH and mild thyrotoxicosis prior to pregnancy may have continuous hyperthyroidism with additional change due to the series of human chorionic gonadotropin secretion during pregnancy.

Nausea and vomiting of pregnancy and hyperemesis gravidarum

Nausea and vomiting of pregnancy (NVP) is a common condition that affects as many as 70% of pregnant women. Although no consensus definition is available for hyperemesis gravidarum (HG), it is typically viewed as the severe form of NVP and has been reported to occur in 0.3-10.8% of pregnant women. HG can be associated with poor maternal, fetal and child outcomes. The majority of women with NVP can be managed with dietary and lifestyle changes, but more than one-third of patients experience clinically relevant symptoms that may require fluid and vitamin supplementation and/or antiemetic therapy such as, for example, combined doxylamine/pyridoxine, which is not teratogenic and may be effective in treating NVP. Ondansetron is commonly used to treat HG, but studies are urgently needed to determine whether it is safer and more effective than using first-line antiemetics. Thiamine (vitamin B1) should be introduced following protocols to prevent refeeding syndrome and Wernicke encephalopathy. Recent advances in the genetic study of NVP and HG suggest a placental component to the aetiology by implicating common variants in genes encoding placental proteins (namely GDF15 and IGFBP7) and hormone receptors (namely GFRAL and PGR). New studies on aetiology, diagnosis, management and treatment are under way. In the next decade, progress in these areas may improve maternal quality of life and limit the adverse outcomes associated with HG.

Highly conserved intracellular H208 residue influences agonist selectivity in bitter taste receptor T2R14

Bitter taste receptors (T2Rs) are a specialized class of cell membrane receptors of the G protein-coupled receptor family and perform a crucial role in chemosensation. The 25 T2Rs in humans are activated by structurally diverse ligands of plant, animal and microbial origin. The mechanisms of activation of these receptors are poorly understood. Therefore, identification of structural determinants of T2Rs that regulate its efficacy could be beneficial in understanding the molecular mechanisms of T2R activation. In this work, we characterized a highly conserved histidine (H208), present at TM5-ICL3 region of T2R14 and its role in agonist-induced T2R14 signaling. Surprisingly, mutation of the conserved H208 (H208A) did not result in increased basal activity of T2R14, in contrast to similar H206A mutation in T2R4 that showed constitutive or basal activity. However, H208A mutation in T2R14 resulted in an increase in agonist-induced efficacy for Flufenamic acid (FFA). Interestingly, H208A did not affect the potency of another T2R14 agonist Diphenhydramine (DPH). The H208R compensatory mutation showed FFA response similar to wild-type T2R14. Molecular modeling suggests a FFA-induced shift in TM3 and TM5 helices of H208A, which changes the network of interactions connecting TM5-ICL3-TM6. This report identifies a crucial residue on the intracellular surface of T2Rs that is involved in bitter ligand selectivity. It also highlights the varied roles carried out by some conserved residues in different T2Rs.

Associations of vomiting and antiemetic use in pregnancy with levels of circulating GDF15 early in the second trimester: A nested case-control study

Background: Although nausea and vomiting are very common in pregnancy, their pathogenesis is poorly understood. We tested the hypothesis that circulating growth and differentiation factor 15 (GDF15) concentrations in early pregnancy, whose gene is implicated in hyperemesis gravidarum, are associated with nausea and vomiting. Methods: Blood samples for the measurement of GDF15 and human chorionic gonadotrophin (hCG) concentrations were obtained early in the second trimester (median 15.1 (interquartile range 14.4-15.7) weeks) of pregnancy from 791 women from the Cambridge Baby Growth Study, a prospective pregnancy and birth cohort. During each trimester participants completed a questionnaire which included questions about nausea, vomiting and antiemetic use. Associations with pre-pregnancy body mass indexes (BMI) were validated in 231 pregnant NIPTeR Study participants. Results: Circulating GDF15 concentrations were higher in women reporting vomiting in the second trimester than in women reporting no pregnancy nausea or vomiting: 11,581 (10,977-12,219) (n=175) vs. 10,593 (10,066-11,147) (n=193) pg/mL, p=0.02). In women who took antiemetic drugs during pregnancy (n=11) the GDF15 levels were also raised 13,157 (10,558-16,394) pg/mL (p =0.04). Serum GFD15 concentrations were strongly positively correlated with hCG levels but were inversely correlated with maternal BMIs, a finding replicated in the NIPTeR Study. Conclusions: Week 15 serum GDF15 concentrations are positively associated with second trimester vomiting and maternal antiemetic use in pregnancy. Given GDF15's site of action in the chemoreceptor trigger zone of the brainstem and its genetic associations with hyperemesis gravidarum, these data support the concept that GDF15 may be playing a pathogenic role in pregnancy-associated vomiting.

Graves' disease and pregnancy

This section deals with the specificities of managing Graves' disease during pregnancy. Graves' disease incurs risks of fetal, neonatal and maternal complications that are rare but may be severe: fetal hyper- or hypothyroidism, usually first showing as fetal goiter, neonatal dysthyroidism, premature birth and pre-eclampsia. Treatment during pregnancy is based on antithyroid drugs alone, without association to levothyroxine. An history of Graves' disease, whether treated radically or not, with persistent maternal anti-TSH-receptor antibodies must be well identified. Fetal monitoring should be initiated in a multidisciplinary framework that should be continued throughout pregnancy. Neonatal monitoring is also crucial if the mother still shows anti-TSH-receptor antibodies at end of pregnancy or underwent antithyroid treatment. The risk of recurrence of hyperthyroidism in the weeks following delivery requires maternal monitoring. The long-term neuropsychological progression of children of mothers with Graves' disease is poorly known.

Variables Contributing to Thyroid (Dys)Function in Pregnant Women: More than Thyroid Antibodies?

Variability in thyroid function in pregnant women is the result of 2 main determinants, each accounting for approximately half of it. The first is the genetically determined part of which the knowledge increases fast, but most remains to be discovered. The second determinant is caused by an ensemble of variables of which thyroid autoimmunity is the best known, but also by others such as parity, smoking, age, and BMI. More recently, new candidate variables have been proposed, such as iron, endocrine disruptors, and the ethnicity of the pregnant women. In the future, the diagnosis and treatment of thyroid (dys)function may be optimized by the use of each individual's pituitary-thyroid set point, corrected with a factor taking into account the impact of nongenetically determined variables.

Thyrotropin receptor, still much to be learned from the patients

In the absence of crystal available for the full-length thyrotropin receptor, knowledge of its structure and functioning has benefitted from the identification and characterization of mutations in patients with various thyroid dysfunctions. The characterization of activating mutations has contributed to the elaboration of a model involving the extracellular domain of the receptor as an inverse tethered agonist which, upon binding of the ligand, relieves the transmembrane domain from an inhibiting interaction and activates it. The models derived from comparisons with other receptors, enriched with the information provided by the study of mutations, have proven useful for the design of small-molecule agonists and antagonists that may be used in the future to treat thyroid dysfunctions. In this review, extrathyroidal expression of the thyrotropin receptor is described, the role of which is still poorly defined.

Gain-of-function mutations in G-protein-coupled receptor genes associated with human endocrine disorders

The human genome encodes more than 700 G-protein-coupled receptors (GPCRs), many of which are involved in hormone secretion. To date, more than 100 gain-of-function (activating) mutations in at least ten genes for GPCRs, in addition to several loss-of-function mutations, have been implicated in human endocrine disorders. Previously reported gain-of-function GPCR mutations comprise various missense substitutions, frameshift mutations, intragenic inframe deletions and copy-number gains. Such mutations appear in both germline and somatic tumour cells, and lead to various hormonal abnormalities reflecting excessive receptor activity. Phenotypic consequences of these mutations include distinctive endocrine syndromes, as well as relatively common hormonal abnormalities. Such mutations encode hyperfunctioning receptors with increased constitutive activity, broadened ligand specificity, increased ligand sensitivity and/or delayed receptor desensitization. Furthermore, recent studies proposed a paradoxical gain-of-function mechanism caused by inactive GPCR mutants. Molecular diagnosis of GPCR activating mutations serves to improve the clinical management of mutation-positive patients. This review aims to introduce new aspects regarding gain-of-function mutations in GPCR genes associated with endocrine disorders.

Severe thyrotoxicosis in an infant revealing familial nonautoimmune hyperthyroidism with a novel (C672W) stimulating thyrotropin receptor germline mutation

We describe severe thyrotoxicosis in young members of a family with nonautoimmune hyperthyroidism caused by a C672W germline mutation in exon 10 of TSHR gene. In this family, lack of genotype‐phenotype correlation and anticipation across generations could be linked to an increased iodine intake as recently observed in France.

Genetic analysis of hyperemesis gravidarum reveals association with intracellular calcium release channel (RYR2)

Hyperemesis Gravidarum (HG), severe nausea/vomiting in pregnancy (NVP), can cause poor maternal/fetal outcomes. Genetic predisposition suggests the genetic component is essential in discovering an etiology. We performed whole-exome sequencing of 5 families followed by analysis of variants in 584 cases/431 controls. Variants in RYR2 segregated with disease in 2 families. The novel variant L3277R was not found in any case/control. The rare variant, G1886S was more common in cases (p = 0.046) and extreme cases (p = 0.023). Replication of G1886S using Norwegian/Australian data was supportive. Common variants rs790899 and rs1891246 were significantly associated with HG and weight loss. Copy-number analysis revealed a deletion in a patient. RYR2 encodes an intracellular calcium release channel involved in vomiting, cyclic-vomiting syndrome, and is a thyroid hormone target gene. Additionally, RYR2 is a downstream drug target of Inderal, used to treat HG and CVS. Thus, herein we provide genetic evidence for a pathway and therapy for HG.

Nausea and vomiting of pregnancy - What's new?

Nausea and vomiting of pregnancy (NVP) is one of the most common disorders of pregnancy. The symptoms occur predominantly during the first trimester, although in a subgroup of patients they can continue throughout the entire pregnancy and can affect the woman's quality of life. A small percentage of women develop a severe form of NVP called hyperemesis gravidarum (HG) that if left untreated may lead to significant maternal morbidity and adverse birth outcomes. Overall, the morbidity in pregnant women with NVP is significant, although it tends to be underestimated. The pathogenesis of NVP remains unclear, but there is consensus that the disorder is multifactorial and that various genetic, endocrine and infectious factors may be involved. The treatment of NVP can be challenging as the optimal targets for therapy are not known. Currently, the therapy used depends on the severity of the disorder and it is focused on improving the symptoms while minimizing risks to mother and fetus. Therapies range from dietary changes, pharmacologic treatment or hospitalization with intravenous fluid replacement and nutrition therapy. The aims of this review are 1) to provide an overview of NVP, 2) to present possible links between the most important factors associated with the pathogenesis of NVP and 3) to discuss the effectiveness and safety of the pharmacologic and non-pharmacologic options available to treat this disorder.

Benign thyroid disease in pregnancy: A state of the art review

Thyroid dysfunction is the commonest endocrine disorder in pregnancy apart from diabetes. Thyroid hormones are essential for fetal brain development in the embryonic phase. Maternal thyroid dysfunction during pregnancy may have significant adverse maternal and fetal outcomes such as preterm delivery, preeclampsia, miscarriage and low birth weight. In this review we discuss the effect of thyroid disease on pregnancy and the current evidence on the management of different thyroid conditions in pregnancy and postpartum to improve fetal and neonatal outcomes, with special reference to existing guidelines on the topic which we dissect, critique and compare with each other. Overt hypothyroidism and hyperthyroidism should be treated appropriately in pregnancy, aiming to maintain euthyroidism. Subclinical hypothyroidism is often pragmatically treated with levothyroxine, although it has not been definitively proven whether this alters maternal or fetal outcomes. Subclinical hyperthyroidism does not usually require treatment and the possibility of non-thyroidal illness or gestational thyrotoxicosis should be considered. Autoimmune thyroid diseases tend to improve during pregnancy but commonly flare-up or emerge in the post-partum period. Accordingly, thyroid auto-antibodies tend to decrease with pregnancy progression. Postpartum thyroiditis should be managed based on the clinical symptoms rather than abnormal biochemical results.