Clinical features and genetic analysis of four Brazilian kindreds with resistance to thyroid hormone

Assessment of Cardiometabolic Risk Factors and Insulin Sensitivity by Hyperinsulinemic-Euglycemic Clamp in Resistance to Thyroid Hormone β Syndrome

Background: Resistance to thyroid hormone beta (RTHβ) is a rare disease resulting from mutations in the THRB gene, characterized by reduced T3 action in tissues with high thyroid hormone receptor β expression. Thyroid hormones regulate body composition and metabolism in general, and increased or decreased hormone levels are associated with insulin resistance. This study evaluated the presence of cardiometabolic risk factors and insulin sensitivity in patients with RTHβ. Methods: In all, 16 patients, 8 adults (52.3 ± 16.3 years of age) and 8 children (10.9 ± 3.9 years of age), were compared to 28 control individuals matched for age, sex, and body mass index (BMI). Anthropometry evaluation and blood samples were collected for glycemia, lipids, insulin, interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), leptin, adiponectin, ultrasensitive C-reactive protein (CRPus), free thyroxine, total triiodothyronine, thyrotropin, and anti-thyroid peroxidase measurements. Body composition was assessed using dual-emission X-ray absorptiometry and bioimpedance. Insulin sensitivity was evaluated in adult patients and controls using the hyperinsulinemic-euglycemic clamp (HEC), whereas homeostasis model assessment of insulin resistance (HOMA-IR) was calculated in all individuals studied. Results: Patients and controls presented similar weight, BMI, abdominal perimeter, and total fat body mass. Patients with RTHβ demonstrated higher total cholesterol (TC), p = 0.04, and low-density lipoprotein cholesterol (LDL-C), p = 0.03, but no alteration was observed in other parameters associated with metabolic risk, such as leptin, TNF-α, and CRPus. Two adult patients met the criteria for metabolic syndrome. There was no evidence of insulin resistance assessed by HEC or HOMA-IR. Elevated IL-6 levels were observed in patients with RTHβ. Conclusion: Using HEC as the gold standard method, no evidence of reduced insulin sensitivity in skeletal muscle was documented in RTHβ adult patients; however, higher levels of TC and LDL-C were observed in these patients, which suggest the need for active monitoring of this abnormality to minimize cardiometabolic risk. In addition, we demonstrated, for the first time, that the increase in IL-6 levels in patients with RTHβ is probably secondary to metabolic causes as they have normal levels of TNF-α and CRPus, which may contribute to an increase in cardiovascular risk. A larger number of patients must be studied to confirm these results.

An overview of thyroid function tests in subjects with resistance to thyroid hormone and related disorders

Confirmation of sustained syndrome of inappropriate secretion of thyrotropin (SITSH) is a milestone in diagnosis of β type of resistance to thyroid hormone (RTHβ). The differential diagnoses of RTHβ include TSH-producing pituitary adenoma (TSHoma) and familial dysalbuminemic hyperthyroxinemia (FDH), which also present SITSH. Recently, patients with RTHα caused by a mutation in thyroid hormone receptor α were reported and they did not present SITSH but a decline in the serum T4/T3 ratio. This review was aimed to overview thyroid function tests in RTH and related disorders. First, the characteristics of the thyroid function in RTHβ, TSHoma, and FDH obtained from a Japanese database are summarized. Second, the degrees of SITSH in patients with truncations and frameshifts were compared with those in patients with single amino acid deletions and single amino acid substitutions obtained from the literature. Third, the degrees of SITSH in homozygous patients were compared with those in heterozygous patients with cognate mutations. Finally, the FT3/FT4 ratios in RTHα are summarized. In principle, the TSH values in FDH were within the normal range and apparent FT4 values in FDH were much higher than in RTHβ and TSHoma. The FT3/FT4 values in RTHβ were significantly lower than in TSHoma. The degrees of SITSH in patients with truncations and frameshifts were more severe than those in patients with single amino acid deletions and single amino acid substitutions, and those in homozygous patients were more severe than those in heterozygous patients with cognate mutations. The FT3/FT4 ratios in RTHα were higher than 1.0.

Clinical, Genetic, and Protein Structural Aspects of Familial Dysalbuminemic Hyperthyroxinemia and Hypertriiodothyroninemia

Familial dysalbuminemic hyperthyroxinemia (FDH-T4) and hypertriiodothyroninemia (FDH-T3) are dominantly inherited syndromes characterized by a high concentration of thyroid hormone in the blood stream. The syndromes do not cause disease, because the concentration of free hormone is normal, but affected individuals are at risk of erroneous treatment. FDH-T4 is the most common cause of euthyroid hyperthyroxinemia in Caucasian populations in which its prevalence is about 1 in 10,000 individuals, but the prevalence can be much higher in some ethnic groups. The condition is caused by a genetic variant of human serum albumin (HSA); Arg218 is mutated to histidine, proline, or serine or Arg222 is changed to isoleucine. The disorder is characterized by greater elevation in serum l-thyroxine (T4) than in serum triiodothyronine (T3); T4 can be increased by a factor 8-15. The high serum concentration of T4 is due to modification of a binding site located in the N-terminal half of HSA (in subdomain IIA). Thus, mutating Arg218 or Arg222 for a smaller amino acid reduces the steric restrictions in the site and creates a high-affinity binding site. The mutations can also affect binding of other ligands and can perhaps cause modified pharmacokinetics of albumin-binding drugs. In normal HSA, the high-affinity site has another location (in subdomain IIIB). Different locations of these sites imply that persons with and without FDH-T4 can have different types of interactions, and thereby complications, when given albumin-binding drugs. FDH-T3 is caused by a leucine to proline mutation in position 66 of HSA, which results in a large increment of the binding affinity for T3 but not for T4. For avoiding unwanted treatment of euthyroid persons with hyperthyroxinemia or hypertriiodothyroninemia, protein sequencing and/or sequencing of the albumin gene should be performed.

Role of Thyroid Hormones in Skeletal Development and Bone Maintenance

The skeleton is an exquisitely sensitive and archetypal T3-target tissue that demonstrates the critical role for thyroid hormones during development, linear growth, and adult bone turnover and maintenance. Thyrotoxicosis is an established cause of secondary osteoporosis, and abnormal thyroid hormone signaling has recently been identified as a novel risk factor for osteoarthritis. Skeletal phenotypes in genetically modified mice have faithfully reproduced genetic disorders in humans, revealing the complex physiological relationship between centrally regulated thyroid status and the peripheral actions of thyroid hormones. Studies in mutant mice also established the paradigm that T3 exerts anabolic actions during growth and catabolic effects on adult bone. Thus, the skeleton represents an ideal physiological system in which to characterize thyroid hormone transport, metabolism, and action during development and adulthood and in response to injury. Future analysis of T3 action in individual skeletal cell lineages will provide new insights into cell-specific molecular mechanisms and may ultimately identify novel therapeutic targets for chronic degenerative diseases such as osteoporosis and osteoarthritis. This review provides a comprehensive analysis of the current state of the art.

Resistance to thyroid hormone due to mutations in the THRB gene impairs bone mass and affects calcium and phosphorus homeostasis

CONTEXT

Resistance to thyroid hormone (RTH) is an inherited syndrome of reduced tissue responsiveness to thyroid hormone, which is usually due to mutations in the thyroid hormone receptor β gene (THRB). Few studies have been conducted to investigate bone and mineral metabolism in RTH.

OBJECTIVE

The objective of the study was to evaluate the clinical and biochemical parameters related to bone and mineral metabolism in RTH due to mutations in the THRB gene (RTHβ).

DESIGN AND PARTICIPANTS

We conducted a cross-sectional study on 14 patients with RTHβ (RTHG), eight adults and six children, and 24 control subjects (CG).

OUTCOMES

Serum measures included total calcium (TCa), inorganic phosphate (iP), alkaline phosphatase (AP), parathyroid hormone (PTH), 25-hydroxyvitamin D (25OHD), osteocalcin (OC), carboxyterminal telopeptide (CTX), and fibroblast growth factor 23 (FGF-23). We estimated the renal threshold phosphate concentration (TmPO4/GFR) and assessed bone mass using dual X-ray absorptiometry.

RESULTS

Adults and children with RTH showed higher serum levels of TCa than controls (P=.029 and, P=.018 respectively). However, only children with RTH exhibited lower serum levels of iP than controls (P=.048). FGF-23 was higher in RTHβ children (P=.04). RTHβ adults had lower whole-body (P=.01) and lumbar spine (P=.01) bone mineral density than control subjects. The same pattern was observed when the results were expressed as Z-scores between groups, with a lower value in RTHG than in CG for the lumbar spine of adults (P=.03). No difference was observed between groups in PTH, 25OHD, AP, OC, and CTX.

CONCLUSION

Biochemical abnormalities are seen in children with RTH (Low iP, high FGF23), while high calcium (with normal UCa) is seen in RTH subjects of all ages, and later on, in adult life, low BMD is seen. Considering that the TRα1 isoform is the predominant TR in the skeleton, we hypothesize that probably these patients may exhibit enhanced calcium flux from bone to circulation. Our data represent a challenge for new studies to unveil the control of calcium and phosphorus homeostasis and fracture risk in these patients.

Is there a role for inherited TRβ mutation in human carcinogenesis? [corrected]

Resistance to thyroid hormone (RTH) is a rare autosomal dominant inherited disorder characterized by end-organ reduced sensitivity to thyroid hormone. This syndrome is caused by mutations of the thyroid hormone receptor (TR) β gene, and its clinical presentation is quite variable. Goiter is reported to be the most common finding. A close association of TRβ mutations with human cancers has become apparent, but the role of TRβ mutants in the carcinogenesis is still undefined. Moreover, higher TSH levels, described in RTH syndrome, are correlated with increased risk of thyroid malignancy, whereas TSH receptor stimulation is likely to be involved in tumor progression. We report here an illustrative case of a 29 year-old patient with RTH caused by a mutation in exon 9 (A317T) of TRβ gene, who presented multicentric papillary thyroid cancer. We review the literature on this uncommon feature, and discuss the potential role of this mutation on human tumorigenesis, as well as the challenges in patient follow-up.

Thyroid hormone resistance detected by routine neonatal screening

We report the clinical and laboratory findings, and molecular analysis of a Brazilian patient with resistance to thyroid hormone syndrome (RTH) detected by neonatal screening. The index case was born at term by normal delivery with 2,920 g and 45 cm. TSH of the neonatal screening test performed on the 5(th) day of life was of 13.1 µU/mL (cut-off = 10 µU/mL). In a confirmatory test, serum TSH level was 4.3 µU/mL, total T4 was 19 µg/dL (confirmed in another sample, Total T4 = > 24.0 µg/dL), free T4 was 3.7 ηg/dL, and free T3 was 6.7 pg/mL. Direct sequencing of the beta thyroid hormone receptor gene revealed mutation c.1357C>A (P453T), confirming the diagnosis of RHT. Family study demonstrated the presence of RTH in his 1-year-and-3-month-old sister, in his 35-year-old father, and in his 68-year-old paternal grandfather. All of them had goiter and only his father had received an erroneous diagnosis of hyperthyroidism. The present case shows that clinical evaluation and a judicious interpretation of total T4/free T4 concentrations in a newborn recalled due to slightly altered neonatal TSH can contribute to the diagnosis of RTH.

E449X mutation in the thyroid hormone receptor beta associated with autoimmune thyroid disease and severe neuropsychomotor involvement

OBJECTIVE

To report the clinical and molecular aspects of a patient with a diagnosis of Resistance to Thyroid Hormone (RTH) harboring the E449X mutation associated with autoimmune thyroid disease and severe neuropsychomotor retardation.

METHODS

We present a case report including clinical and laboratory findings, and molecular analysis of a Brazilian patient with RTH.

RESULTS

A 23-year old male presented hyperactivity disorder, attention deficit, delayed neuropsychomotor development, and goiter. Since the age of 1 year and 8 months, his mother had sought medical care for her son for the investigation of delayed neuropsychomotor development associated with irritability, aggressiveness, recurrent headache, profuse sudoresis, intermittent diarrhea, polyphagia, goiter, and low weight. Laboratory tests revealed normal TSH, increased T3, T4, antithyroglobulin and antimicrosomal antibody titers. Increasing doses of levothyroxine were prescribed, reaching 200 microg/day, without significant changes in his clinical-laboratory picture. Increasing doses of tiratricol were introduced, with a clear clinical improvement of aggressiveness, hyperactivity, tremor of the extremities, and greater weight gain. Molecular study revealed a nonsense mutation in exon 10, in which a substitution of a guanine to tyrosine in nucleotide 1345 (codon 449) generates the stop codon TAA, confirming the diagnosis of RTH.

CONCLUSION

This patient has severe neuropsychomotor retardation not observed in a single previous report with the same mutation. This may reflect the lack of a genotype-phenotype correlation in affected cases with this syndrome, suggesting that genetic variability of factors other than beta receptor of thyroid hormone (TRbeta) might modulate the phenotype of RTH.

Genotyping of resistance to thyroid hormone in South American population. Identification of seven novel missense mutations in the human thyroid hormone receptor beta gene

Thyroid Hormone Receptor beta (THRB) defects, typically transmitted as autosomal dominant traits, cause Resistance to Thyroid Hormone (RTH). We analyzed the THRB gene in thirteen South American patients with clinical evidence RTH from eleven unrelated families. Sequence analysis revealed seven novel missense mutations. Four novel mutations were identified in exon 9. The first, a c.991A>G transition which originates a substitution of asparagine by aspartic acid (p.N331D). The second nucleotide alteration consists of a guanine to cytosine transversion at position 1003 (c.1003G>C) and results in substitution of the alanine at codon 335 by proline (p.A335P). The third mutation, a c.1022T>C transition produces a change of leucine by proline (p.L341P). The fourth mutation detected in exon 9 was a c.1036C>T transition which replaces the leucine at codon 346 by phenylalanine (p.L346F). The sequencing of the exon 10 detected three novel missense mutations. The first, a c.1293A>G transition changing isoleucine 431 for methionine (p.I431M). The second, the cytosine at position 1339 was replaced by adenine (c.1339C>A) resulting in the replacement of proline by threonine (p.P447T). The third mutation detected in exon 10 was a c.1358C>T transition resulting in the substitution of proline at codon 453 by leucine (p.P453L). Finally, sequencing analysis of the THRB gene revealed three substitutions previously described (p.A268G, p.P453T and p.F459C). The p.P453T was found in two patients. In conclusion, we report thirteen patients with RTH caused by heterozygous mutations of the THRB gene. Seven of the identified mutations correspond to novel substitutions.

Hypothalamic-pituitary axis and peripheral tissue responses to TRH stimulation and liothyronine suppression tests in normal subjects evaluated by current methods

OBJECTIVE

To reevaluate the responses of thyrotropin-releasing hormone (TRH) stimulation test in baseline condition as well as after the administration of graded supraphysiological doses of liothyronine (L-T(3)) in normal subjects.

DESIGN

To assess various parameters related to the hypothalamic-pituitary axis and peripheral tissue responses to L-T(3) in 22 normal individuals (median age: 30.5 years). Subjects were submitted to an intravenous TRH test at baseline condition and also to the oral administration of sequential and graded doses of L-T(3) (50, 100, and 200 microg/day), each given over 3 days, at an outpatient clinic. Blood samples were obtained for thyrotropin (TSH) and prolactin (PRL) at basal and then 15, 30, and 60 minutes after the TRH injection. Effects of L-T(3) administration on cholesterol, creatine kinase, retinol, ferritin, and sex hormone-binding globulin (SHBG) were also measured at basal and after the oral administration of L-T(3).

MAIN OUTCOME

TRH administration resulted in an increase of 4- to 14-fold rise in serum TSH (8.3 +/- 2.5-fold), and in a slight rise in serum PRL concentrations (3.8 +/- 1.5-fold). Administration of graded doses of triiodothyronine (T(3)) resulted in a dose-dependent suppression of TSH and PRL. Basal thyroxine-binding globulin (TBG) and cholesterol levels decreased, and ferritin and SHBG increased after L-T(3) administration, while creatine kinase and retinol did not change throughout the study. There was a positive correlation between basal TSH and TSH peak response to TRH at basal condition and after each sequential L-T(3) doses. On the other hand, TSH peak response to the TRH test did not predict cholesterol, TBG, ferritin, or SHBG values.

CONCLUSION

Using the current methods on hormone and biochemical analysis, we standardized the response of many parameters to TRH stimulation test after sequential and graded T(3) suppression test in normal subjects. Our data suggest that the evaluation of the responses of the hypothalamus-pituitary axis to TRH test as well as the impact of L-T(3) on peripheral tissues were not modified by the current methods.