Syndromes of Resistance to Thyroid Hormone Action

2024 European Thyroid Association Guidelines on diagnosis and management of genetic disorders of thyroid hormone transport, metabolism and action

Impaired sensitivity to thyroid hormones encompasses disorders with defective transport of hormones into cells, reduced hormone metabolism, and resistance to hormone action. Mediated by heritable single-gene defects, these rare conditions exhibit different patterns of discordant thyroid function associated with multisystem phenotypes. In this context, challenges include ruling out other causes of biochemical discordance, making a diagnosis using clinical features together with the identification of pathogenic variants in causal genes, and managing these rare disorders with a limited evidence base. For each condition, the present guidelines aim to inform clinical practice by summarizing key clinical features and useful investigations, criteria for molecular genetic diagnosis, and pathways for management and therapy. Specific, key recommendations were developed by combining the best research evidence available with the knowledge and clinical experience of panel members, to achieve a consensus.

Cardiovascular morbidity and mortality in patients in Wales, UK with resistance to thyroid hormone β (RTHβ): a linked-record cohort study

BACKGROUND

Individuals with resistance to thyroid hormone owing to mutations in the thyroid hormone receptor β gene (RTHβ) exhibit impaired tissue sensitivity to thyroid hormones, but retain sensitivity in cardiac tissue. Long-term health and survival outcomes in this rare disorder have not been evaluated. We investigated all-cause mortality and cardiovascular event risk in a cohort of patients with RTHβ, followed-up in UK endocrine clinics.

METHODS

In a retrospective cohort design, we linked genetically confirmed patients with RTHβ and age-matched and sex-matched population controls to outcomes in datasets within the Welsh Secure Anonymised Information Linkage (SAIL) Databank. Kaplan-Meier and Cox regression models analysed associations of RTHβ with all-cause mortality and cardiovascular events.

FINDINGS

We identified 61 patients with a genetic diagnosis of RTHβ between Jan 1, 1997, and Dec 31, 2019, and matched them with 2750 controls. Compared with controls, patients exhibited increased risks for all-cause mortality (hazard ratio [HR] 2·84, 95% CI 1·59-5·08), atrial fibrillation (10·56, 4·72-23·63), heart failure (HR 6·35, 95% CI 2·26-17·86), and major adverse cardiovascular events (MACE), comprising cardiovascular death, acute myocardial infarction, heart failure, or strokes (HR 3·49, 95% CI 2·04-5·99). The median age of first occurrence of any adverse event was 11 years earlier in patients (56 years, 95% CI 44-65) compared with controls (67 years, 65-70). Cubic spline analyses showed positive associations between FT4 concentrations at diagnosis and mortality or MACE, with FT4 concentration of 30 pmol/L or greater conferring increased risk. Compared with no intervention, treatment with antithyroid drugs, surgery or radioiodine gland ablation, or thyroxine did not control thyroid hormone excess.

INTERPRETATION

We have documented reduced survival and increased cardiovascular morbidity in a cohort of patients with RTHβ for the first time. These outcomes might be driven by lifelong cardiac exposure to thyroid hormone excess; and effective therapies, targeting hormone resistant pathways, could potentially curtail this risk.

FUNDING

Royal College of Physicians, Wellcome Trust Investigator Award, and NIHR Cambridge Biomedical Research Centre.

A novel variant of THRβ and its 4-year clinical course in a Korean boy with resistance to thyroid hormone

Thyroid hormone resistance (RTH) is characterized by a decreased sensitivity of target tissues to thyroid hormones due to a defect in the THRα- and THRβ-encoded thyroid hormone receptors (THRs). The clinical manifestations range from no symptoms to simple goiter and hypo- or hyperthyroidism, depending on the receptor subtype distribution in the tissues. Here, we report the case of a thyroid hormone-resistant 12-month-old boy carrying a novel THRβ variant who was initially diagnosed with congenital hypothyroidism. An extensive evaluation revealed increased free T4 level and inappropriately increased thyroid-stimulating hormone (TSH) level; a normal lipid profile, sex hormone-binding globulin, and free alpha subunit of TSH; exaggerated TSH response to THR; and no radiological evidence of pituitary adenoma. A targeted next-generation sequencing panel identified a heterozygote c.993T>G (p.Asn331Lys) mutation in the THRβ gene. During the first year of life, a higher dose of levothyroxine was administered to the patient due to uncompensated RTH. Levothyroxine treatment was continued after 3 years to maintain TSH level <5 mIU/mL, but the observed weight gain was poor, height increase was insufficient, and bone development was delayed. However, neither hyperactivity nor developmental delay was observed. Patients with RTH exhibit various clinical features. Due to its heterogeneous nature, genetic test for accurate diagnosis is important to provide proper management.

Atrial Fibrillation with Heart Failure in a Case with Resistance to Thyroid Hormone Due to a Rare Thyroid Hormone Receptor β Gene Mutation

Resistance to thyroid hormone (RTH) is a rare disease typically associated with elevated levels of thyroid hormones and non-suppressed thyroid stimulating hormones. The most common cause of RTH is thyroid hormone receptor β (THRβ) gene mutation. Most individuals with RTH are considered clinical euthyroid. We report a family with a rare heterozygous point mutation, c.959G>T, (p.R320L) of the THRβ gene. The proband developed atrial fibrillation and life-threatening heart failure with pulmonary edema, which was quite different from previously reported THRβ gene mutations. Considering the rareness of RTH and the heterogeneity of its phenotypes, our report allows for a better understanding of the manifestation and management of patients with RTH and THRβ gene mutation.

Factors influencing the levothyroxine dose in the hormone replacement therapy of primary hypothyroidism in adults

Levothyroxine (LT4) is a safe, effective means of hormone replacement therapy for hypothyroidism. Here, we review the pharmaceutical, pathophysiological and behavioural factors influencing the absorption, distribution, metabolism and excretion of LT4. Any factor that alters the state of the epithelium in the stomach or small intestine will reduce and/or slow absorption of LT4; these include ulcerative colitis, coeliac disease, bariatric surgery, Helicobacter pylori infection, food intolerance, gastritis, mineral supplements, dietary fibre, resins, and various drugs. Once in the circulation, LT4 is almost fully bound to plasma proteins. Although free T4 (FT4) and liothyronine concentrations are extensively buffered, it is possible that drug- or disorder-induced changes in plasma proteins levels can modify free hormone levels. The data on the clinical significance of genetic variants in deiodinase genes are contradictory, and wide-scale genotyping of hypothyroid patients is not currently justified. We developed a decision tree for the physician faced with an abnormally high thyroid-stimulating hormone (TSH) level in a patient reporting adequate compliance with the recommended LT4 dose. The physician should review medications, the medical history and the serum FT4 level and check for acute adrenal insufficiency, heterophilic anti-TSH antibodies, antibodies against gastric and intestinal components (gastric parietal cells, endomysium, and tissue transglutaminase 2), and Helicobacter pylori infection. The next step is an LT4 pharmacodynamic absorption test; poor LT4 absorption should prompt a consultation with a gastroenterologist and (depending on the findings) an increase in the LT4 dose level. An in-depth etiological investigation can reveal visceral disorders and, especially, digestive tract disorders.

Discovery of a Highly Selective and H435R-Sensitive Thyroid Hormone Receptor β Agonist

The design and development of agonists selectively targeting thyroid hormone receptor β (TRβ) and TRβ mutants remain challenging tasks. In this study, we first adopted the strategy of breaking the "His-Phe switch" to solve two problems, simultaneously. A structure-based design approach was successfully utilized to obtain compound 16g, which is a potent TRβ agonist (EC₅₀: 21.0 nM, 85.0% of the maximum efficacy of 1) with outstanding selectivity for TRβ over TRα and also effectively activates the TRβ^H435R mutant. Then, we developed a highly efficient synthetic method for 16g. Our serials of cocrystal structures revealed detailed structural mechanisms in overcoming subtype selectivity and rescuing the H435R mutation. 16g also showed excellent lipid metabolism, safety, metabolic stability, and pharmacokinetic properties. Collectively, 16g is a well-characterized selective and mutation-sensitive TRβ agonist for further investigating its function in treating dyslipidemia, nonalcoholic steatohepatitis (NASH), and resistance to thyroid hormone (RTH).

Higher maternal thyroid resistance indices were associated with increased neonatal thyroid-stimulating hormone- analyses based on the Huizhou mother-infant cohort

OBJECTIVES

This study aimed to explore the relationship of maternal thyroid function and thyroid resistance parameters with neonatal thyroid-stimulating hormone (TSH).

METHODS

This work was a longitudinal study. Singleton pregnant women without a history of thyroid disorders were recruited in their first prenatal visit from October 2018 to June 2020. Maternal thyroid markers including TSH, free triiodothyronine (FT3), free thyroxine (FT4), and neonatal TSH were tested in the clinical laboratory of the hospital by electrochemiluminescence immunoassay. Thyroid resistance indices including Thyroid Feedback Quantile-based Index (TFQI), TSH index (TSHI), and thyrotroph T4 resistance index (TT4RI) were estimated in accordance with maternal FT4 and TSH levels. Multivariable linear and logistic regression was applied to explore the associations of maternal thyroid indices with infantile TSH level.

RESULTS

A total of 3,210 mothers and 2,991 newborns with valid TSH data were included for analysis. Multivariable linear regression indicated that maternal thyroid variables were significantly and positively associated with neonatal TSH levels with standardized coefficients of 0.085 for TSH, 0.102 for FT3, 0.100 for FT4, 0.076 for TSHI, 0.087 for TFQI, and 0.089 for TT4RI (all P < 0.001). Compared with the lowest quartile, the highest quartile of TSHI [odds ratio (OR) = 1.590, 95% CI: 0.928-2.724; P_trend = 0.025], TFQI (OR = 1.746, 95% CI: 1.005-3.034; P_trend = 0.016), and TT4RI (OR = 1.730, 95% CI: 1.021-2.934; P_trend = 0.030) were significantly associated with an increased risk of elevated neonatal TSH (>5 mIU/L) in a dose-response manner.

CONCLUSION

The longitudinal data demonstrated that maternal thyroid resistance indices and thyroid hormones in the first half of gestation were positively associated with neonatal TSH levels. The findings offered an additionally practical recommendation to improve the current screening algorithms for congenital hypothyroidism.

Developments in pediatrics in 2020: choices in allergy, autoinflammatory disorders, critical care, endocrinology, genetics, infectious diseases, microbiota, neonatology, neurology, nutrition, ortopedics, respiratory tract illnesses and rheumatology

In this article, we describe the advances in the field of pediatrics that have been published in the Italian Journal of Pediatrics in 2020. We report progresses in understanding allergy, autoinflammatory disorders, critical care, endocrinology, genetics, infectious diseases, microbiota, neonatology, neurology, nutrition, orthopedics, respiratory tract illnesses, rheumatology in childhood.

TSH adenoma and syndrome of resistance to thyroid hormones-Two cases report of syndrome of inappropriate secretion of thyrotropin

SITSH (syndrome of inappropriate secretion of thyrotropin) is a rare clinical state defined as uninhibited serum thyroid stimulating hormone in the presence of elevated thyroid hormone. This state is complicated and mainly caused by the abnormal feedback of hypothalamus-pituitary thyroid axis. The TSH adenoma (TSH-oma) and resistance to thyroid hormones (RTH) are the main etiologies of SITSH. As is well known that the treatment strategies of RTH and TSH-oma are apparently different, thus identifying the difference between RTH and TSH-oma is of great significance for the diagnosis and treatment of SITSH. CASE DESCRIPTION: A 62-year-old man with a state of elevated thyroid hormones and inappropriate elevated serum TSH level was hospitalized in 2016. Results of the pituitary enhanced magnetic resonance imaging and the somatostatin test respectively demonstrated a space-occupying lesion of pituitary and an elevated serum sex hormone binding globulin (SHBG) and inhibited TSH secretion, which indicated the occurrence of TSH-oma. In 2019, a 23-year-old girl with a state of elevated thyroid hormones and inappropriate normal serum TSH was hospitalized. Interestingly, whole exome sequencing detection suggested a pathogenic mutation in thyroid hormone receptor β (THRB) gene, which has been shown to be associated with RTH. CONCLUSIONS: The difference between TSH-oma and RTH ought to be clarified for their accurate diagnose and treatment. The clinical experiences of the two cases reported here suggest that more detail information such as family medical history, serum SHBG level, and THRB gene test is helpful for the diagnose and treatment of TSH-oma and RTH. Additionally, we also summarized the identification points, diagnosis process, and treatment strategies for these two rare diseases.

Clinical and laboratory aspects of 3,3',5'-triiodothyronine (reverse T3)

Reverse T3 (3,3',5'-triiodothyronine or rT3) is the third most abundant iodothyronine circulating in human blood and is produced by the inner ring deiodination of the pro-hormone thyroxine (T4). Unlike the more abundant and active metabolite T3, the measurement of serum rT3 is yet to find a routine clinical application. As rT3 binds weakly to the T3 thyroid nuclear hormone receptors, it is thought to represent an inactive end-product of thyroid hormone metabolism, diverting T4 away from T3 production. The analysis of serum rT3 has, up until recently, been measured by competitive radioimmunoassay, but these methods have been superseded by mass-spectrometric methods which are less susceptible to interference from other more abundant iodothyronines. Serum rT3 concentration is increased as part of the non-thyroidal illness syndrome, and by administration of common medications such as amiodarone which inhibit the metabolism of rT3. Serum rT3 concentration is also affected by genetic conditions that affect the iodothyronine deiodinases, as well as thyroid transporters and transport proteins. Analysis of rT3 can provide a useful diagnostic fingerprint for these conditions. rT3 has been shown to bind extra-nuclear iodothyronine receptors with a potential role in cell proliferation; however, the clinical relevance of these findings awaits further study.

Temporal Pole Responds to Subtle Changes in Local Thyroid Hormone Signaling

To study thyroid hormone (TH) signaling in the human brain, we analyzed published microarray data sets of the temporal pole (Brodmann area 38) of 19 deceased donors. An index of TH signaling built on the expression of 19 well known TH-responsive genes in mouse brains (T3S+) varied from 0.92 to 1.1. After Factor analysis, T3S+ correlated independently with the expression of TH transporters (MCT8, LAT2), TH receptor (TR) beta and TR coregulators (CARM1, MED1, KAT2B, SRC2, SRC3, NCOR2a). Unexpectedly, no correlation was found between T3S+ vs DIO2, DIO3, SRC1, or TRα. An unbiased systematic analysis of the entire transcriptome identified a set of 1649 genes (set #1) with strong positive correlation with T3S+ (r > 0.75). Factor analysis of set #1 identified 2 sets of genes that correlated independently with T3S+, sets #2 (329 genes) and #3 (191 genes). When processed through the Molecular Signatures Data Base (MSigDB), both sets #2 and #3 were enriched with Gene Ontology (GO)-sets related to synaptic transmission and metabolic processes. Ranking individual human brain donors according to their T3S+ led us to identify 1262 genes (set #4) with >1.3-fold higher expression in the top half. The analysis of the overlapped genes between sets #1 and #4 resulted in 769 genes (set #5), which have a very similar MSigDB signature as sets #2 and #3. In conclusion, gene expression in the human temporal pole can be assessed through T3S+ and fluctuates with subtle variations in local TH signaling.

Hyperthyroxinemia with a non-suppressed TSH: how to confidently reach a diagnosis in this clinical conundrum

Disorders of thyroid function are among the commonest referrals to endocrinology. While interpretation of thyroid function testing is usually straightforward, accurate interpretation becomes significantly more challenging when the parameters do not behave as would be expected in normal negative feedback. In such cases, uncertainty regarding further investigation and management arises. An important abnormal pattern encountered in clinical practice is that of high normal or raised free thyroxine (fT4) with inappropriately non-suppressed or elevated thyroid-stimulating hormone (TSH). In this short review using two clinical vignettes, we examine the diagnostic approach in such cases. A diagnostic algorithm is proposed to ensure that a definitive diagnosis is reached in these challenging cases.