Thyroid hormone resistance and large goiter mimicking infiltrative carcinoma in a pediatric patient

OBJECTIVES

Resistance to thyroid hormone (RTH) is a genetic condition, caused by mutations in the thyroid hormone receptor gene and characterized by impaired end organ responsiveness to thyroid hormone. Here we describe a novel case of THR associated with large goiter mimicking infiltrative c.

CASE PRESENTATION

A 13-year-old male with a hyperthyroid phenotype of RTH diagnosed as a toddler, on methimazole and nadolol therapies presented with an increase in goiter size and possible nodule. Thyroid ultrasound was concerning for a diffuse infiltrative process or malignancy. Methimazole was discontinued and he underwent further imaging, fine needle aspiration and core biopsies. Biopsy results were reassuring and imaging findings were subsequently attributed to RTH rather than malignancy. He started every other day liothyronine therapy, which led to a decrease in goiter size, thyroglobulin level, and improvement of hyperthyroid symptoms.

CONCLUSIONS

This is the first case to our knowledge describing the above thyroid imaging findings in association with RTH. It also adds important information to the pediatric literature regarding management of the hyperthyroid phenotype of RTH, including the role of liothyronine therapy.

Diagnosis of Resistance to Thyroid Hormone due to a Rare Mutation in the Thyroid Hormone Receptor Beta Gene in a Patient Previously Presumed to Have Graves' Disease

Clinicians may confuse an impaired sensitivity to thyroid hormone with hyperthyroidism and offer an inappropriate treatment. We report a diagnosis of resistance to thyroid hormone (RTH) caused by a rare mutation in the thyroid hormone receptor beta gene in a patient previously presumed to have Graves' disease. We have found only one published case of a novel point mutation, c.749T>C (p.Ile250Thr variant) associated with 50% reduction in thyroid hormone receptor binding affinity for triiodothyronine in the I250T mutant; it was found in this patient. A 66-year-old male veteran, with a history of non-ischemic cardiomyopathy and arrhythmias, was referred by a cardiologist with concerns for a possible thyrotropin (TSH) adenoma on account of elevated TSH and free thyroxine (FT4) levels. Pituitary imaging was negative. He was previously treated with radioiodine for presumptive Graves' disease in the civilian sector. Examination revealed a goiter with no nodules. Repeat TSH and FT4 levels were elevated and also free triiodothyronine (FT3) and reverse triiodothyronine. These findings and other test results were consistent with RTH, which was confirmed by genetic testing. Mutation analysis showed the patient to be heterozygous for the p.Ile250Thr variant. He later developed hypothyroidism. Resistance to thyroid hormone can be misdiagnosed as hyperthyroidism with consequent inappropriate treatment. Treatment is not needed in most RTH-beta patients. Thyroid ablation should generally be avoided. Clinicians must be cautious whenever they encounter concurrent elevation of TSH, FT4, and FT3. This RTH-beta patient has a rare I250T mutant of the thyroid hormone receptor beta gene, the second reported case in the literature.

Thyroid hormone resistance resulting from a novel mutation in the THRB gene in a Chinese child: A case report

INTRODUCTION

Thyroid hormone resistance (RTH) (mim # 188570) is a rare autosomal dominant genetic disorder characterized by reduced thyroid hormone response in target tissues. The clinical manifestations of RTH vary from no symptoms to symptoms of thyroid hormone deficiency to symptoms of thyroid hormone excess.

PATIENT CONCERN AND CLINICAL FINDINGS

A 24-month-old girl presented with growth retardation, tachycardia, and persistently elevated thyroid hormones despite antithyroid treatment.

DIAGNOSIS/INTERVENTION/OUTCOMES

The patient was diagnosed with RTH, after whole exon gene sequencing, found a de novo missense mutation (c.1375T > G,p.Phe459Val) in a novel locus of the thyroid hormone receptor beta gene. She had only mild growth retardation, so the decision was made to monitor her development without intervention. At her last follow-up at 5 years and 8 months of age, she continued to show growth retardation (-2 standard deviation below age-appropriate levels), in addition to delayed language development. Her comprehension ability and heart rate have remained normal.

CONCLUSIONS

We report a mild case of RTH caused by a novel thyroid hormone receptor beta gene mutation. RTH should be considered in the differential diagnosis of abnormal serum thyroxine levels during neonatal screening.

Resistance to Thyroid Hormones: A Case-Series Study

The aim of the study is to describe the clinical features of two unrelated patients with resistance to thyroid hormones (RTH), the first, a total thyroidectomized patient, and the second, a pregnant woman. We report the features found in her newborn who also showed RTH. Patient 1 is a 38-year-old man with total thyroidectomy managed for excessive thyroid stimulating hormone (TSH) production, which poorly responded to the replacement therapy. He was found with a THRβ c.1378G>A p.(Glu460Lys) heterozygous mutation, which was also present in other members of his family (son, brother, and father). Interestingly, Patient 1 had hypertension, dyslipidemia, and hepatic steatosis, which have been recently suggested as RTH-related comorbidities. Patient 2 is a 32-year-old pregnant woman with multinodular goiter, and the THRβ heterozygous variant c.959G>C, that, to the best of our knowledge, has been reported in literature only once. Her newborn had tachycardia and increased thyroid hormone levels, and showed the same mutation. After delivery, high parathyroid hormone (PTH) and calcium serum levels were found in Patient 2 and the scintigraphy showed the presence of adenoma of a parathyroid gland. This case-series study provides a practical example of the management of RTH in a thyroidectomized patient, a pregnant woman, and a newborn. A novel RTH pathogenic mutation is described for the second time in literature. Furthermore, the importance of metabolic assessment in patients with RTHβ has been highlighted and the possible correlation between RTH and primary hyperparathyroidism is discussed.

Clinically Symptomatic Resistance to Thyroid Hormone β Syndrome Because of THRB Gene Mosaicism

CONTEXT

Resistance to thyroid hormone β syndrome (RTHβ) is caused by pathogenic variants in the THRB gene, but such variants are found in only 85% of cases. We report the case of a patient with RTHβ phenotype but for whom we found a pathogenic variant of the THRB gene in a mosaic state.

CASE DESCRIPTION

The patient is a 52-year-old woman with clinical and biological signs of RTHβ. Symptoms included asthenia, cardiac palpitations, and diarrhea. Repeated thyroid function tests showed an elevated serum TSH, elevated serum free T4, and variably normal or slightly elevated serum fT3. Pituitary magnetic resonance imaging was normal, and the thyrotropin-releasing hormone test result was compatible with the diagnosis of RTHβ syndrome. Initial Sanger sequencing on blood samples could not highlight the presence of a mosaic variant because of insufficient sensitivity. When next-generation sequencing became accessible, blood samples were retested and we found a known pathogenic variant: c.949G > A; p.(ala317Thr), with an allelic frequency of 12%. Other samples from tissues of different embryological origin were also tested and found an allelic frequency of 5.7%, 17.9%, 9.9%, 6.4%, and 0% on urine tests, oral swab, nasal mucosa swab, skin biopsy, and conjunctival swab, respectively. Cloning confirmed the allelic frequency observed.

CONCLUSIONS

We highlight that a pathogenic variant in a mosaic state in the THRB gene may be the cause of an authentic RTHβ syndrome. High-throughput sequencing of multiple tissues eases the detection of pathogenic variant in a mosaic state and allows the correct diagnosis of patients with true RTHβ, thus avoiding patient mismanagement.

[Thyroxine replacement therapy in patients with thyroid cancer and thyroid hormone resistance syndrome]

Resistance to thyroid hormone (RTH) is a genetic syndrome defined by an impaired sensitivity to thyroid hormones. It is characterized by discrepancies between the blood levels of thyroid hormones (FT3, FT4) and TSH, and by the coexistence of hypothyroidism and hyperthyroidism symptoms. Here we describe the case of a patient affected with thyroid cancer and RTH in whom it was difficult to obtain a good control of TSH after total thyroidectomy despite high doses of thyroxine replacement therapy. This represents a unique model to improve the understanding of the alterations in the feedback mechanism in patients with RTH and to optimize the replacement therapy in patients with concomitant thyroid cancer who need adequate TSH control.

Thyroid Hormone Resistance: Multicentrical Case Series Study

Resistance to thyroid hormone syndrome (RTHS) is defined as increased thyroxine and triiodothyronine associated with normal or increased thyrotropin. This is usually due to a pathogenic variant of the gene coding for thyroid hormone receptor B (THRB). THRB is a rare genetic disorder characterized by an altered response of target tissue to the thyroid hormone action. Retrospective cross-sectional observational study with diagnosis of RTHS evaluated in secondary and tertiary hospitals for 6 years, from 2014 to 2020, in order to describe variables including age, sex, anthropometric data, clinical and biochemical characteristics of patients, who were divided according to age, in a pediatric group from 0 to 14 years (index cases), and an adult group composed of adult relatives of index cases. A molecular analysis of the THRB gene was performed. The total retrospective cohort included 7 pediatric patients and 15 adults. We found 22 cases with a clear male predominance (14/22). Mean age is 24.8 years old (22 days-70 years). Patients were referred because of symptoms 18.2% (4/22), analysis results 22.7% (5/22), or familial study 59.1% (13/22). About 31.8% (7/22) cases show goiter, 31.8% (7/22) sympathetic symptoms and 13.6% (3/22) abnormalities in behavior. In most cases, 77.3%, (17/22) show familial background of thyroid abnormalities. It is important to remark that 18.2% (4/22) relatives received previous incorrect treatments such as thyroidectomy, because of wrong diagnosis. In conclusion, a better understanding of RTHS, its prompt molecular diagnosis and genetic counseling, could avoid unnecessary tests and inappropriate treatments.

Reduced Sensitivity to Thyroid Hormone Is Associated with Diabetes and Hypertension

CONTEXT

Recently, reduced sensitivity to thyroid hormone as a more common finding in the general population and its possible association with metabolic parameters has been the focus of attention.

OBJECTIVE

The objective was to evaluate the cross-sectional association of thyroid hormone sensitivity with diabetes, metabolic syndrome (MetS), and its components.

METHODS

The study included a Tehranian representative sample of 5124 subjects aged ≥20 years participating in the Tehran Thyroid Study (2008-2011). Body weight, waist circumference, and blood pressure (BP) were measured, and serum concentrations of lipids and lipoproteins, fasting blood glucose, insulin, free thyroxine (fT4), and thyrotropin (TSH) were assayed. Thyroid hormone resistance was calculated by the Thyroid Feedback Quantile-based Index (TFQI) and Iranian-referenced Parametric TFQI (PTFQI) and compared with 2 other indices: Thyrotroph T4 Resistance Index (TT4RI) and TSH Index.

RESULTS

TFQI was significantly associated with high BP MetS criterion (OR = 1.14, 95% CI: 1.06, 1.23) and diabetes mellitus (OR = 1.16, 95% CI: 1.04, 1. 30, P = .009) in euthyroid subjects after adjusting for age, sex, smoking, physical activity, body mass index, and Homeostasis Model Assessment Index for Insulin Resistance. TFQI was not associated with new-onset diabetes contrary to known diabetes in subgroup analysis. The results were similar for PTFQI. TSHI (OR = 1.22, 95% CI: 1.08, 1.38, P = .001) and TT4RI (OR = 1.08, 95% CI: 1.01, 1.16, P < .001) were associated only with high BP in euthyroid subjects.

CONCLUSION

The new TFQI index seems to be the indicator of reduced sensitivity to thyroid hormone most suitable to associate its population variations with diabetes and hypertension in euthyroid subjects; however, interpretation for diabetes should be concerned with cautions, necessitating future studies.

Early Diagnosis and Treatment of an Infant with a Novel Thyroid Hormone Receptor α Gene (pC380SfsX9) Mutation

Resistance to thyroid hormone alpha (RTHα) is caused by mutations in thyroid hormone receptor α (THRA). Little is known about the natural history and treatment of RTHα, and diagnosis before the age of 1 year has not been previously reported. A de novo heterozygous THRA mutation (pC380SfsX9) was identified in a 10-month-old female investigated for developmental delay, hypotonia, macrocephaly, and severe constipation. Treatment with levothyroxine was accompanied by an appropriate rise in thyroxine (T4), triiodothyronine (T3), as well as decrease in thyrotropin levels and in the T3/T4 ratio with a trend toward normalization of peripheral markers of thyroid hormone action. THRA pC380SfsX9 results in extreme RTHα.

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.

Update on resistance to thyroid hormone syndromeβ

Resistance to thyroid hormone syndrome (RTH) is an autosomal dominant or recessive genetic disease caused by mutation of either the thyroid hormone receptorβ (THR-β) gene or the thyroid hormone receptorα (THR-α) gene. RTH due to mutations of the THR-β gene (hereafter, RTH-β) is characterized by a decreased response of the target tissue to thyroid hormone, increased serum levels of free triiodothyronine (FT3) and/or free thyroxine (FT4), and inappropriate secretion of thyroid-stimulating hormone (TSH, normal or elevated). Clinical manifestations of RTH-β vary from hyperthyroidism to hypothyroidism or simple goiter, and RTH-β is often misdiagnosed clinically. The present review was prepared for the purpose of expanding knowledge of RTH-β in order to reduce the rate of misdiagnosis.

Diagnosing Thyrotropin-Secreting Pituitary Adenomas by Short-Term Somatostatin Analogue Test

Background: Diagnosis of thyrotropin (TSH)-secreting pituitary adenomas (TSHoma) before surgery remains a challenge, especially for microadenomas. We aimed to establish a short-term somatostatin analogue (SSA) test to differentiate TSHomas from other causes of syndromes of inappropriate secretion of TSH (IST), mainly resistance to thyroid hormone β (RTHβ). Materials and Methods: We first evaluated the sensitivity and specificity of SSA test in a training cohort (TSHoma, n = 32; RTHβ, n = 20). The test was then validated in an independent cohort (TSHoma, n = 9; RTHβ, n = 2). We finally applied the SSA test in 12 perceptively enrolled IST cases with negative imaging findings and absent thyroid hormone receptor beta (THRB) mutations or mixed hormone imbalances. Results: Both TSHoma and RTHβ patients showed a decrease of TSH at the start of the SSA test, but the velocity of the TSH suppression slowly decreased in RTHβ patients after 2 hours. The suppression ratio of TSH at 24 hours versus 2 and 0 hours was significantly greater in TSHoma patients compared with RTHβ patients (70.58% ± 18.6% vs. 6.01% ± 25.41%, p < 0.0001, 79.83% ± 12.79% vs. 51.16% ± 13.62%, p < 0.0001, respectively). The 24- versus 2-hour suppression ratio showed the best diagnostic accuracy at a cut point of 44.46% in the training cohort, with a sensitivity of 95.00%, a specificity of 93.75%, and a positive predictive value (PPV) of 88.89%. The accuracy was confirmed in the validation cohort. Three out of 12 patients in the prospective cohort showed a TSH suppression ratio greater than 44.46% and all developed microadenomas during follow-up. Conclusions: A short-term SSA test provides an alternative diagnostic approach for TSHomas. A positive SSA test result is suggestive for a TSHoma even before positive findings become apparent on pituitary imaging. However, studies including larger number of patients, especially those with RTHβ, are needed to confirm our findings.

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.

Thyroid hormone resistance from newborns to adults: a Spanish experience

OBJECTIVE

Thyroid hormone resistance (RTH β) is a rare genetic disorder characterized by an altered response of target tissue to the action of thyroid hormone. Few studies on RTH β have been carried out in southern European populations. We aimed to describe the clinical and genetic characteristics at the time of diagnosis in a Spanish cohort of patients with genetically confirmed RTH β, with ages ranging from newborns to adults.

METHODS

Retrospective multicenter study of 28 patients who were genetically confirmed as RTH β. Clinical and biochemical data were collected from the reference centers, and the studied variables included age, sex, anthropometric data, clinical characteristics and biochemical results. In the Basque country, a simultaneous analysis of TSH and T4 is carried out in the program for the screening of inborn errors of metabolism. A molecular analysis of the thyroid hormone beta (THRB) gene was performed.

RESULTS

The total cohort included 20 adults and eight pediatric patients (six newborns). Of the total, 5 (17.8%) were diagnosed by clinical characteristics (goiter, hypertension or tachycardia), 13 (46.4%) were analyzed in the context of a family study and 10 (35.7%) were diagnosed after obtaining an altered fT4 and/or TSH level in a biochemical analysis performed due to clinical symptoms unrelated to RTH β. Four of the newborns included in the series were diagnosed by the result of neonatal screening, which allows us to estimate a minimum local incidence of RTH β of 1/18,750 live newborns. The genetic analysis showed the presence of 12 different heterozygous mutations in the THRB gene.

CONCLUSIONS

We report the clinical and genetic characteristics of a Spanish RTH β cohort, from neonates to adults. We also describe one novel mutation in the THRB gene as the cause of the disease. The simultaneous analysis of TSH and T4 carried out in the program for the screening of inborn errors of metabolism facilitates the early diagnosis of RTH β in newborns and has allowed us to estimate a minimum local incidence of RTH of 1/18,750 live newborns.

A novel thyroid hormone receptor alpha gene mutation, clinic characteristics, and follow-up findings in a patient with thyroid hormone resistance

Thyroid hormone receptor alpha (THRA) gene mutation is a thyroid hormone resistance syndrome characterized by near-normal thyroid function tests and tissue-specific hypothyroidism. In this case study, we report a novel de novo p.G291S heterozygous mutation in the THRA gene was detected at mutation analysis. A 4-year-old male patient was admitted due to short stature, motor-mental retardation, and constipation. At physical examination, coarse facial appearance, eyelid edema, pallor, and umbilical hernia were observed. Primary thyroid hormone resistance should be considered in patients with phenotypically hypothyroid features. Laboratory analysis found moderate elevation in free triiodothyronine (T3) levels, normochromic normocytic anemia, and elevated creatine kinase levels. In conclusion, THRA gene mutation should be considered in patients with clinical hypothyroid findings and increased/moderately elevated free T3, decreased/ normal free thyroxine, normal thyroid-stimulating hormone levels, and increased muscle enzymes.

Two Mutations in Thyroid Hormone Receptor Beta Gene (P453A and C36Y) in a Family with Resistance to Thyroid Hormone with Comorbid Myotonic Dystrophy

The co-occurrence of resistance to thyroid hormone beta (RTHβ) and myotonic dystrophy type 1 (DM1) was observed in a Japanese family. Two mutations, P453A and C36Y, were identified in the thyroid hormone receptor beta (THRB) gene. Whereas family members with THRB^P453A exhibited RTHβ, two members with THRB^C36Y but without THRB^P453A had normal thyroid function. Two members, one with RTHβ and the other without, had a triplet expansion in the dystrophia myotonia protein kinase gene, a hallmark of DM1. The member with both RTHβ and DM1 developed atrial fibrillation at the age of 16 years, suggesting a synergistic impact on the heart.

Assessing the clinical and molecular diagnosis of inherited forms of impaired sensitivity to thyroid hormone from a single tertiary center

AIM

Resistance to thyroid hormone (RTH), characterized by persistent hyperthyroxinemia with non-suppressed thyrotropin (TSH), is mostly caused by mutations in thyroid hormone receptor beta gene (THRB). Two differential diagnoses should be considered due to similar clinical and laboratory findings: TSH-producing pituitary adenoma (TPA) and Familial Dysalbuminemic Hyperthyroxinemia (FDH). The aim of this study is to describe our single tertiary center experience in the molecular diagnosis of RTH in Brazilian patients, analyzing their clinical and laboratory characteristics and the most common differential diagnosis.

SUBJECTS AND METHODS

We enrolled 30 subjects with clinical and laboratory features of RTH. Patient´s evaluations included clinical examination, thyroid hormone profile and imaging tests. Sequencing analysis for THRB hot spot region was conducted on all patients, and those without mutations in beta isoform of the thyroid hormone receptor (TRβ) (non-TR-RTH) were investigated for albumin gene (ALB) mutation.

RESULTS

Seventeen patients presented mutations in TRβ (RTHβ); six were non-TR-RTH, three had a diagnosis of FDH with a mutation in ALB, and four were diagnosed with TPA. Two characteristics were different to what is commonly described in the literature: higher serum TSH levels in RTHβ patients when compared to the non-TR-RTH group, but this difference did not extend to free T4 (FT4) level; also the percentage of non-TR-RTH was higher than what was reported in other series.

CONCLUSION

In the present series, most cases were RTHβ with higher levels of TSH. We described three novel mutations in THRB (p.M313V, p.R320G and p.R438P) and the first patients with FDH molecular diagnosis (p.R242H) documented in Brazil.

Clinical and Molecular Characteristics of Eight Israeli Families with Thyroid Hormone Receptor Beta Mutations

BACKGROUND

Reduced sensitivity to thyroid hormone (RSTH) syndrome describes a group of rare heterogeneous genetic disorders. Precise diagnosis is essential to avoid unnecessary treatment.

OBJECTIVES

To identify and characterize previously undiagnosed patients with RSTH in Israel.

METHODS

Patients with suspected RSTH throughout Israel were referred for study. After clinical evaluation, genomic DNA was obtained and all coding exons of the thyroid hormone receptor beta (THRB) gene were sequenced. If mutations were found, all available blood relatives were evaluated. The common polymorphism rs2596623, a putative intronic regulatory variant, was also genotyped. Genotype/phenotype correlations were sought, and the effect of mutation status on pregnancy outcome was determined.

RESULTS

Eight mutations (one novel; two de-novo, six dominant) were identified in eight probands and 13 family members. Clinical and genetic features were similar to those reported in other populations. Previous suggestions that rs2596623 predicts clinical features were not confirmed. There was no evidence of increased risk of miscarriage or fetal viability. Mothers carrying a THRB mutation tended to have increased gestational hypertension and low weight gain during pregnancy. Their affected offspring had increased risk of small-for-gestational age and poor postnatal weight gain.

CONCLUSIONS

Clinical heterogeneity due to THRB mutations cannot be explained by the variant rs2596623. Mothers and newborns with THRB mutations seem to be at increased risk of certain complications, such as gestational hypertension and poor intrauterine and postnatal growth. However, these issues are usually mild, suggesting that routine intervention to regulate thyroid hormone levels may not be warranted in these patients.

Pituitary resistance to thyroid hormone caused by a novel mutation (H435A) in the thyroid hormone receptor beta: A case report

RATIONALE

In patients with pituitary thyroid hormone resistance, the ability of the pituitary gland to detect (and down-regulate) the increase of triiodothyronine is selectively impaired, while the periphery remains sensitive to triiodothyronine levels, producing symptoms of peripheral thyrotoxicity. Subsequently, there is no feedback of pituitary production of thyroid-stimulating hormone (TSH), which is responsible for this hyperthyroidism.

PATIENT CONCERNS

We report a case of a 46-year-old Chinese woman diagnosed with a thyroid nodule, with normal thyroid function. She underwent conventional subtotal thyroidectomy, and replacement therapy (levothyroxine) was used for as convention. However, it was later proven that she had pituitary resistance to thyroid hormone, as supra-physiological doses of levothyroxine were required to normalize TSH levels, which resulted in peripheral thyrotoxicity.

DIAGNOSES

Based on the patient's symptoms, laboratory tests results, imaging examinations, and genetic analysis (which noted a gene mutation), a diagnosis of pituitary resistance to thyroid hormones was confirmed.

INTERVENTIONS

The dose of levothyroxine was adjusted periodically and β-adrenergic blocker was used as symptomatic treatment.

OUTCOMES

The outcome in the reported case has been satisfactory despite the persistence of non-suppressed TSH.

LESSONS

An inappropriate level of TSH should always be evaluated. We found a new mutation (H435A) of the thyroid hormone receptor beta gene, which allowed for the establishment of a definitive diagnosis.

Prenatal Diagnosis of Resistance to Thyroid Hormone and Its Clinical Implications

CONTEXT

Resistance to thyroid hormone-β (RTH-β) is an autosomal dominant disorder characterized by reduced sensitivity of target tissues to thyroid hormones (THs). Individuals with RTH-β have high TH levels usually due to mutations in the TH receptor-β (THRB) gene. The management of RTH-β during pregnancy is challenging, as wild-type (WT) fetuses born to RTH-β mothers have low birth weight and suppressed postnatal thyroid-stimulating hormone (TSH), due to intrauterine exposure to excess TH.

OBJECTIVE

To determine birth weight and postnatal TSH of WT fetuses carried by mothers with RTH-β whose fT4 levels were maintained below 20% of the upper limit of normal (ULN).

DESIGN

Retrospective chart review.

SETTING

Academic institution in collaboration with off-site hospitals and private practices.

PATIENTS

Thirteen women harboring THRB gene mutations were evaluated during 18 pregnancies.

INTERVENTION

Prenatal genetic diagnosis by amniocentesis. Women carrying WT fetuses were given the option of treatment with antithyroid medication by their treating physicians with the aim to avoid serum fT4 levels above 20% of the ULN.

RESULTS

No significant difference was found in birth weight corrected for gestational age and in serum TSH levels at birth between WT and RTH-β infants born to RTH-β mothers.

CONCLUSIONS

Prenatal diagnosis may play an important role in the management of RTH-β during pregnancy. Aiming for maternal fT4 levels not above 50% of the ULN in RTH-β mothers carrying WT fetuses seems to be a prudent approach that prevents the otherwise expected low birth weight and postnatal TSH suppression.

Contrasting Phenotypes in Resistance to Thyroid Hormone Alpha Correlate with Divergent Properties of Thyroid Hormone Receptor α1 Mutant Proteins

BACKGROUND

Resistance to thyroid hormone alpha (RTHα), a disorder characterized by tissue-selective hypothyroidism and near-normal thyroid function tests due to thyroid receptor alpha gene mutations, is rare but probably under-recognized. This study sought to correlate the clinical characteristics and response to thyroxine (T4) therapy in two adolescent RTHα patients with the properties of the THRA mutation, affecting both TRα1 and TRα2 proteins, they harbored.

METHODS

Clinical, auxological, biochemical, and physiological parameters were assessed in each patient at baseline and after T4 therapy.

RESULTS

Heterozygous THRA mutations occurring de novo were identified in a 17-year-old male (patient P1; c.788C>T, p.A263V mutation) investigated for mild pubertal delay and in a 15-year-old male (patient P2; c.821T>C, p.L274P mutation) with short stature (0.4th centile), skeletal dysplasia, dysmorphic facies, and global developmental delay. Both individuals exhibited macrocephaly, delayed dentition, and constipation, together with a subnormal T4/triiodothyronine (T3) ratio, low reverse T3 levels, and mild anemia. When studied in vitro, A263V mutant TRα1 was transcriptionally impaired and inhibited the function of its wild-type counterpart at low (0.01-10 nM) T3 levels, with higher T3 concentrations (100 nM-1 μM) reversing dysfunction and such dominant negative inhibition. In contrast, L274P mutant TRα1 was transcriptionally inert, exerting significant dominant negative activity, only overcome with 10 μM of T3. Mirroring this, normal expression of KLF9, a TH-responsive target gene, was achieved in A263V mutation-containing peripheral blood mononuclear cells following 1 μM of T3 exposure, but with markedly reduced expression levels in L274P mutation-containing peripheral blood mononuclear cells, even with 10 μM of T3. Following T4 therapy, growth, body composition, dyspraxia, and constipation improved in P1, whereas growth retardation and constipation in P2 were unchanged. Neither A263V nor L274P mutations exhibited gain or loss of function in the TRα2 background, and no additional phenotype attributable to this was discerned.

CONCLUSIONS

This study correlates a milder clinical phenotype and favorable response to T4 therapy in a RTHα patient (P1) with heterozygosity for mutant TRα1 exhibiting partial, T3-reversible, loss of function. In contrast, a more severe clinical phenotype refractory to hormone therapy was evident in another case (P2) associated with severe, virtually irreversible, dysfunction of mutant TRα1.

Resistance to thyroid hormone α, revelation of basic study to clinical consequences

In the past 3 years, 15 patients with resistance to thyroid hormone α (RTHα), nine THRA gene mutations have been reported, reforming classification of RTH. RTHα exhibits distinguished clinical manifestations from RTHβ, including growth retardation, skeletal dysplasia, impaired neurodevelopment, cardiovascular dysfunction, constipation and specific thyroid axis type. This review focuses on possible pathogenesis by revelatory basic science of RTHα animal models in vivo, and patients' mutant thyroid hormone receptor α (TRα) in vitro. Clinical manifestations and L-T4 effects are summarized, showing strong correlation to the severity of mutation mostly within the domain which dominated TR interaction with T3 and its corepressors/coactivators. In particular, we propose the diagnosis clues and promising treatment for clinicians.

Resistance to Thyroid Hormone Alpha in an 18-Month-Old Girl: Clinical, Therapeutic, and Molecular Characteristics

BACKGROUND

Recently, the first patients with resistance to thyroid hormone alpha (RTHα) due to inactivating mutations in the thyroid hormone receptor alpha (TRα) were identified. These patients are characterized by growth retardation, variable motor and cognitive defects, macrocephaly, and abnormal thyroid function tests. The objective was to characterize a young girl (18 months old) with a mutation in both TRα1 and TRα2, and to study the effects of early levothyroxine (LT4) treatment.

METHODS

The patient was assessed clinically and biochemically before and during 12 months of LT4 treatment. In addition, the consequences of the mutation for TRα1/2 receptor function were studied in vitro.

RESULTS

At 18 months of age, the patient presented with axial hypotonia, delayed motor development, severe growth retardation, and abnormally elevated triiodothyronine (T3)/thyroxine (T4) ratios. RTHα was suspected, and concomitantly a c.632A>G/p.D211G missense mutation was identified, affecting both the TRα1 and TRα2 proteins. This mutation was also found in the girl's father. LT4 treatment was started, resulting in a marked improvement of her hypotonia, motor skills, and growth. Functionally, the missense mutation led to decreased transcriptional activity of TRα1, which could be overcome by higher T3 levels in vitro. The mutant TRα1 showed a moderate dominant negative activity on wild type (WT) TRα1. In contrast, WT TRα2 and mutant TRα2 had negligible transcriptional activity and showed no dominant-negative effect over TRα1.

CONCLUSIONS

This report describes the phenotype of a young RTHα patient with a mild TRα mutation before and during early LT4 treatment. Treatment had beneficial effects on her muscle tone, motor development, and growth.

Characteristics of patients with late manifestation of resistance thyroid hormone syndrome: a single-center experience

Resistance to thyroid hormone (RTH) is a rare genetic disease caused by reduced tissue sensitivity to thyroid hormone. The hallmark of RTH is elevated serum levels of thyroid hormone with unsuppressed thyrotropin (TSH). However, the most common form of RTH results from minor defects in the ligand-binding domain or hinge domain of the TRβ gene, resulting in impaired T3-induced transcriptional activity, often showing mild presentation. Early diagnosis can be challenging. The objective of the current study was to characterize this specific group of RTH patients. This was a retrospective study. Patients diagnosed as RTH with TRβ mutations were enrolled in a single institute between 2004 and 2014. A total of 14 patients were diagnosed as RTH with mutation in THβ gene. The median age at diagnosis was 22.5 (IQR: 13.25-32.75). Goiter was the most common clinical finding. TSH was significantly elevated after TRH injection (median peak was 21.83 μIU/l, IQR: 13.59-31.48), 9.2-fold compared to the basal level. We found 10 mutations in TRβ gene, all located in the last four exons, and including one novel mutation, H271D. In vitro study found that H271D mutation reduced TR affinity to T3. Four patients with intact thyroid were diagnosed after 16 years old, defined as late manifestation. Compared to those diagnosed before 10 years old, patients with late manifestation presented with normal growth and mental development. Interestingly, three of them carried R438H mutation. We identified a novel p.H271D mutation in TRβ associated with RTH. Endocrinologists should be alert that RTH is frequently found in euthyroid patients with mild symptoms and often leads to misleading diagnosis as well as inappropriate treatment.

Description of the thyroid hormone resistance syndrome illustrated by such a case, which had two different carcinomas and was mistreated with iodine-131

OBJECTIVE

Hyperthyroidism with increased serum thyroid hormones and also increased thyroid stimulating hormone (TSH) is described as the resistance thyroid hormone (RTH) syndrome. This syndrome may be due to various factors including tumors. We describe the different types of RTH syndrome and mention that this syndrome may be misdiagnosed and mistreated. To illustrate the RTH syndrome we describe such a case which also had two different carcinomas. This case was treated with anti-thyroid drugs, triiodothyroacetic acid and iodine-131 (¹³¹I). In the following 5.5 years after ¹³¹I treatment, TSH progressively increased and was not suppressed by normal doses of L-thyroxine (L-T4). A thyroid nodule was diagnosed as papillary thyroid carcinoma (PTC) and a small cell neuroendocrine carcinoma was diagnosed in the nasal septum. Under L-T4 replacement treatment and after ablation of both carcinomas, TSH returned to normal. Small cell neuroendocrine carcinomas accompanied with PTC, are extremely rare causes of RTH.

CONCLUSION

A description of the resistance to thyroid hormone syndrome is presented and this syndrome is illustrated by a referring case which could be of a selective pituitary type or due to the neuroendocrine tumor.

Diabetes mellitus in a girl with thyroid hormone resistance syndrome: a little recognized interaction between the two diseases

The syndrome of resistance to thyroid hormone (RTH) is characterized by elevated serum free thyroid hormones (FT4 and FT3) in the presence of unsuppressed TSH levels, reflecting resistance to the normal negative feedback mechanisms in the hypothalamus and pituitary. The degree of resistance within peripheral tissues determines whether thyrotoxic clinical features are associated with this condition. Classic features include attention deficit hyperactivity disorder, growth delay, tachycardia, and goiter. However, other features, such as frequent ear, nose and throat infections, hearing deficit, and decreased bone mass have recently been recognized. The phenotype of RTH is variable, with most patients presenting with mild to moderate symptoms. In this report we describe a girl with familiar RTH and diabetes mellitus. This is, to our knowledge, the first report regarding this association. Nearly one year after long-term triiodothyroacetic acid (Triac) therapy, we observed a reduction of thyroid hormone levels with an amelioration of insulin resistance. The possible interactions between these disorders are discussed.

Resistance to thyroid hormone

Resistance to thyroid hormone (RTH) or thyroid hormone action defect (THAD) is the most frequent form of syndromes of reduced sensitivity to thyroid hormone. It is characterized by variable tissue hyposensitivity to thyroid hormone. RTHβ (formerly only RTH) is caused by mutations in the thyroid hormone receptor β gene (THRB). The clinical phenotype reflects the dysbalance between resistance of tissues predominantly expressing the thyroid hormone receptor β-isoforms 1 and 2 and the overstimulation of tissues mainly expressing the thyroid hormone receptor α-isoform to thyroid hormones. The hallmark of RTHβ is goiter, sinus tachycardia, attention deficit hyperactivity disorder in the context of increased levels of triiodothyronine/free thyroxine and nonsuppressed thyroid-stimulating hormone. Only recently have mutations in the thyroid hormone receptor α gene (THRA) been identified causing a new form of RTH, RTHα. The few patients described so far suffered from mental retardation of variable degree, short stature with decreased subischial leg length, chronic constipation and bradycardia. This review provides an overview of clinical, biochemical and genetic aspects of RTHα and RTHβ relevant for diagnosis, treatment and counseling of affected patients and families.

[Thyroid disease caused by receptor abnormality]

Hormone receptor abnormality is a syndrome of an abnormal mechanism caused by defective receptor function in hormone action. Resistance to thyroid hormone is a syndrome in which the responsiveness of the target organ to thyroid hormone is reduced. Resistance to thyroid hormone exhibits unsuppressed thyrotropin(TSH) despite elevated free thyroxin (FT4) and free 3,5,3'-triiodothyronine (FT3), termed the syndrome of the inappropriate secretion of TSH (SITSH). Resistance to thyroid hormone is mainly caused by a mutation in the thyroid hormone receptor beta (TRbeta) gene. Genetic analysis of the TRbeta gene is important to diagnose resistance to thyroid hormone. TSH receptor (TSHR) abnormality is classified as a gain-of-function mutation and loss-of-function mutation. Loss-of-function mutations in the TSHR gene occur as TSH resistance, which is found to have euthyroid hyperthyrotropinemia or hypothyroidism because of the reduced responsiveness of the receptor to TSH. R450H mutation in the TSHR gene is occasionally observed in Japanese patients with TSH resistance. In Japan, it is suggested that analysis of the R450H mutation in the TSHR gene is useful to determine the cause of hyperthyrotropinemia or hypothyroidism.

PRKAR1A and PDE4D mutations cause acrodysostosis but two distinct syndromes with or without GPCR-signaling hormone resistance

CONTEXT

Acrodysostosis is a rare skeletal dysplasia that is associated with multiple resistance to G protein-coupled receptor (GPCR) signaling hormones in a subset of patients. Acrodysostosis is genetically heterogeneous because it results from heterozygous mutations in PRKAR1A or PDE4D, two key actors in the GPCR-cAMP-protein kinase A pathway.

OBJECTIVE

Our objective was to identify the phenotypic features that distinguish the two genotypes causing acrodysostosis.

PATIENTS AND METHODS

Sixteen unrelated patients with acrodysostosis underwent a candidate-gene approach and were investigated for phenotypic features.

RESULTS

All patients had heterozygous de novo mutations. Fourteen patients carried a PRKAR1A mutation (PRKAR1A patients), five each a novel PRKAR1A mutation (p.Q285R, p.G289E, p.A328V, p.R335L, or p.Q372X), nine the reported PRKAR1A p.R368X mutation; two patients harbored a mutation in PDE4D (PDE4D patients) (one novel mutation, p.A227S; one reported, p.E590A). All PRKAR1A, but none of the PDE4D mutated patients were resistant to PTH and TSH. Two PRKAR1A patients each with a novel mutation presented a specific pattern of brachydactyly. One PDE4D patient presented with acroskyphodysplasia. Additional phenotypic differences included mental retardation in PDE4D patients. In addition, we report the presence of pigmented skin lesions in PRKAR1A and PDE4D patients, a feature not yet described in the acrodysostosis entity.

CONCLUSIONS

All PRKAR1A and PDE4D patients present similar bone dysplasia characterizing acrodysostosis. Phenotypic differences, including the presence of resistance to GPCR-cAMP signaling hormones in PRKAR1A but not PDE4D patients, indicate phenotype-genotype correlations and highlight the specific contributions of PRKAR1A and PDE4D in cAMP signaling in different tissues.

[Syndromes of resistance to thyroid hormone and inappropriate secretion of TSH (SITSH)]

Resistance to thyroid hormone (RTH) is a syndrome in which the responsiveness of end organs to thyroid hormone (TH) is reduced. Given that the TH-responsive end-organs include pituitary thyrotrophs, almost all patients with RTH manifest unsuppressed thyrotropin (TSH) despite elevated free-T4 and free-T3 levels. This abnormal finding in the thyroid function test is termed "syndrome of inappropriate secretion of TSH" (SITSH) or "central hyperthyroidism". Patients with TSH-secreting pituitary tumors(TSHoma) also manifest SITSH. Thus, the differential diagnosis of RTH vs. TSHoma is sometimes difficult and challenging. In this review article, the etiology of RTH and diagnostic approach for SITSH are explained and an algorithm for differential diagnosis of RTH vs. TSHoma is proposed.

Variable clinical presentation and outcome in pediatric patients with resistance to thyroid hormone (RTH)

Resistance to thyroid hormone (RTH) is characterized by elevated levels of thyroid hormones, normal or slightly increased TSH levels respondent to TRH, resistance to thyroid hormone administration, and variable clinical expression. To describe the diverse clinical and biochemical findings of six children from five unrelated families with molecular diagnosis of RTH (0.5-12.7 years) and their follow-up (3-20 years). All RTH patients and 4 affected parents' harbored mutations in exons 9 or 10 of the thyroid receptor β gene: p.M313T (de novo), pN331D, p.L341P, p.L346F, and p.P453L. At consultation 5/6 had goiter, 4/6 tachycardia, and 3/5 learning disabilities. Median hormone levels were: T(4) 257.4 nmol/l (NR: 77.2-180.2); FreeT(4) 39.9 pmol/(NR:10.3-28.3); T(3) 4.28 nmol/l (NR:1.23-3.39) TSH 2.8 mUI/l (NR: 0.5-5) always responsive to TRH. TSH levels remained detectable after supraphysiologic T(3) administration while SHBG levels showed a paradoxical decrease in 4/6. Thyroid antibodies, initially present in two subjects, became positive in other two during follow-up. All patients grew normally and presented variable symptoms that were treated according to need. Two patients developed psychiatric disorders. Only one of the four affected parents exhibited clinical signs of RTH (tachycardia and depression). Parent's thyroid profile showed similar TSH and T(3) levels but lower T(4) and FT(4) than their children. RTH has a distinctive biochemical profile with highly variable clinical manifestations and outcomes. Its recognition and molecular characterization avoid misleading diagnosis. Treatment has to be instituted according to each subject's own clinical requirements.

A new mutation in the thyroid hormone receptor gene of a Chinese family with resistance to thyroid hormone

BACKGROUND

Resistance to thyroid hormone (RTH) is a dominant inherited syndrome of reduced tissue responsiveness to thyroid hormone. It is usually due to mutations located at the ligand-binding domain and adjacent hinge region of the thyroid hormone receptor β (TRβ). We report the clinical and laboratory characteristics and the genetic analysis of a patient with this rare disorder and his family members.

METHODS

The clinical presentations and changes of thyroid function tests (TFTs) including magnetic resonance imaging (MRI) of pituitary and other laboratory tests were analysed. TFTs of his family's members were detected as well. Direct DNA sequencing of the TRβ gene was done for those with abnormal TFTs.

RESULTS

The RTH child had goiter, irritability, aggressiveness, and sudoresis. His TFTs showed high levels of circulating free thyroid hormones (FT(4) and FT(3)) and normal thyroid-stimulating hormone (TSH) concentrations. He felt worse when treated as hyperthyroidism (Grave disease) with thiamazole and his clinical presentations got improved obviously when treated as RTH with bromocriptine without obvious advert effect. We identified a novel missense mutation, A317D, located in exon 9 of the gene of this boy and his mother. His mother had not any clinical presentation, but having abnormal TFTs results.

CONCLUSIONS

This patient reported here was concordant with the criteria of RTH. The feature is dysfunction of hypothalamus-pituitary-thyroid axis. A novel mutation was found in the TRβ, A317D, of this family. This research verified the phenomena that there is a clinical heterogeneity within the same mutation of different RTH patients.

Resistance to thyroid hormone accompanied by Graves' disease

Resistance to thyroid hormone (RTH) is characterized by elevated serum levels of thyroid hormones and normal or slightly increased serum thyrotropin (TSH) levels. Recently it has been suggested that chronic TSH stimulation in RTH activates intrathyroidal lymphocytes, leading to thyroid damage and autoimmune thyroid disease (AITD). Therefore, individuals with RTH have an increased likelihood of AITD compared to unaffected relatives. We here report a 33-year-old woman in whom we diagnosed Graves' disease and treated her with thiamazole (MMI). For two years, her TSH levels were suppressed when thyroid hormones were elevated and conversely they were increased when thyroid hormones levels were decreased. These findings were common for a clinical course during treatment for Graves' disease with anti-thyroid drug. However, three years after the initiation of MMI therapy, she had a normal or gradually elevated serum TSH level even though the level of thyroid hormones never decreased, indicating inappropriate secretion of TSH. We concluded she had RTH clinically, and we demonstrated by direct sequence analysis a mutation of the TRβ gene, causing replacement of a glycine (G) with arginine (R) at codon 251. The finding of an elevated TSH level without decreased thyroid hormones should suggest the presence of RTH during therapy of Graves' disease.

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.

A case of resistance to thyroid hormone with thyroid cancer

Resistance to thyroid hormone (RTH) is an autosomal dominant hereditary disorder that is difficult to diagnose because of its rarity and variable clinical features. The magnitude of RTH is caused by mutations in the thyroid hormone receptor beta (TR beta) gene. We recently treated a 38-yr-old woman with RTH who had incidental papillary thyroid carcinoma. She presented with goiter and displayed elevated thyroid hormone levels with an unsuppressed TSH. She was determined to harbor a missense mutation of M310T in exon 9 of the TR beta gene, and diagnosed with generalized RTH. This mutation has not yet been reported in Korea. RTH is very rare and easily overlooked, but should be considered in patients who present with goiter and elevated thyroid hormone levels with an unsuppressed TSH. The association between thyroid cancer and RTH needs further study.

A mutation in thyroid hormone receptor beta causing "resistance to thyroid hormone" in a neonate

Resistance to thyroid hormone (RTH) is an inherited syndrome characterized by reduced tissue responsiveness to thyroid hormones. The main defects are due to mutations in thyroid hormone receptor beta (TRbeta). A male, term neonate was admitted because of indirect hyperbilirubinemia and polycythemia. Physical examination revealed ophtalmopathy. High serum T₄ with unsupressed thyroid stimulating hormone (TSH) levels suggested RTH. In this presented case, A317T mutation was detected on exon 9 of the TRb-1 gene and precise diagnosis had been confirmed with genetic testing. In neonates and infants exhibiting hypo or hyperthyroidism features with increased circulating levels of thyroid hormones with a normal or increased serum TSH concentration should raise the suspicion of RTH.

Resistance to thyroid hormone in a patient with coexisting Graves' disease

BACKGROUND

Resistance to thyroid hormone (RTH) is a rare disorder in which an abnormality in the binding domain of the thyroid hormone receptor results in end-organ insensitivity to the actions of thyroid hormones. This disorder is sometimes misdiagnosed as Graves' disease due to the presence of a goiter with high Iodine-123 thyroid uptake and high levels of total and free thyroid hormones. Additionally, some patients with RTH may experience palpitations or tachycardia. There is a previous report of a patient with pituitary RTH and concurrent Graves' disease.

SUMMARY

We describe a patient who was found to have a goiter with signs and symptoms of hyperthyroidism by his primary care physician. Work-up revealed a low thyroid stimulating hormone (TSH), high thyroid-stimulating immunoglobulins, high Iodine-123 thyroid uptake, as well as increased homogenous activity in both thyroid glands on nuclear scan and a suppressed TSH. Diagnosis of Graves' disease was made, and the patient underwent radioactive ablation of the thyroid gland. The patient subsequently developed hypothyroidism and required a much higher dose of levothyroxine than his weight-based estimate of a full replacement dose to maintain euthyroidism. On 325 micog of daily levothyroxine the patient was clinically euthyroid and had a normal TSH although his levels of T3 and T4 were high. Work-up revealed a mutation in the thyroid hormone beta-receptor gene, consistent with diagnosis of RTH.

CONCLUSIONS

RTH is often misdiagnosed as Graves' disease. However, these disorders can coexist, and the concurrent presence of both disorders in a patient can present diagnostic challenges. A previous report of a patient with Graves' disease associated with RTH was published before gene sequencing could be used to confirm diagnosis of RTH. We present a patient with Graves' disease and concurrent RTH that was confirmed by gene sequencing, showing a mutation in the thyroid hormone receptor beta gene.

Clinical features of primary hyperthyroidism caused by Graves' disease admixed with resistance to thyroid hormone (P453T)

A 34-year-old Japanese woman was referred to the hospital because of general fatigue and palpitations. She was diagnosed as having resistance to thyroid hormone (RTH) and Hashimoto's thyroiditis at the age of 28. She felt general fatigue, palpitations, heat intolerance, and sweating for 6 months. Thyroid function tests demonstrated elevated levels of free triidothyronine (T3) and free thyroxine (T4) that were above detectable ranges and a completely suppressed level of TSH that was below the detectable range. Titers of anti-TSH receptor antibody (TRAb) and thyroid-stimulating antibody (TSAb) were positive. A 20-minute Technetium-m99 pertechnetate thyroid uptake imaging study showed an elevated value of 39.53% and a normal-shaped thyroid gland. These results indicated that Graves' disease (GD) caused primary hyperthyroidism. Pituitary and peripheral tissues responded to the presence of excess thyroid hormone in the patient. Oral administration of methimazole was started and continued for 1 year 10 months, after which it was ceased. Two years after the cessation of methimazole treatment, level of free T4 was elevated compared to reference range, but levels of TSH and free T3 were within normal reference ranges. Titers of TRAb and TSAb remained negative for 2 years. These findings indicated that the patient's GD was in remission. In conclusion, it is difficult to make a differential diagnosis between GD with RTH and GD alone if RTH is not diagnosed before the onset of GD. An antithyroid drug is able to cause the remission of GD with RTH.

Severe psychomotor and metabolic damages caused by a mutant thyroid hormone receptor alpha 1 in mice: can patients with a similar mutation be found and treated?

Individuals suffering from the resistance to thyroid hormone syndrome (RTH) have a mutation in thyroid hormone receptor (TR) beta. Surprisingly, no patient with a mutation in TRalpha1 has been found. To facilitate their identification, animal models with a RTH-like mutation in TRalpha1 have been generated. The mutations introduced into the mouse decrease affinity to ligand, resulting in a 'receptor-mediated hypothyroidism' in tissues expressing the mutant receptor: brain, heart and bone. The mice present minor perturbances in thyroid hormone homeostasis, but show major aberrancies in postnatal development, psychomotor behaviour and metabolism. These parameters are akin to those seen in endemic cretinism and untreated congenital hypothyroidism. Treatment of the mice with high doses of triiodothyronine leads to normalization or amelioration of the dysfunctions when applied at adequate developmental periods.

CONCLUSION

Our studies on mice suggest the existence of a potentially debilitating disease caused by a mutant TRalpha1, and provide insights for identification and treatment of corresponding patients.

Resistance to thyroid hormone in a Turkish child with A317T mutation in the thyroid hormone receptor-beta gene

Resistance to thyroid hormone (RTH) syndrome is a rare disorder usually inherited as an autosomal dominant trait. The combination of elevated serum levels of free thyroid hormones with elevated thyroid-stimulating hormone (TSH) suggest differential diagnoses of RTH, thyroxine-binding globulin abnormalities, familial dysalbuminemic hyperthyroxinemia and TSH-secreting pituitary tumors. We report a patient with RTH in a Turkish family. The diagnosis was confirmed by the identification of a known disease-causing mutation in the thyroid hormone receptor-beta (THRbeta) gene, but is the first published in the Turkish population. Genetic analysis of the mother and the patient yielded a mutation in the THRbeta gene, A317T, due to a base pair substitution of an adenine for a guanine.

Resistance to thyroid hormone with missense mutation (V349M) in the thyroid hormone receptor beta gene

Resistance to thyroid hormone (RTH) is a syndrome characterized by reduced sensitivity to the thyroid hormone. It is generally caused by mutations in the thyroid hormone receptor beta (TR beta) gene. On the basis of its clinical features, two different forms of this syndrome have been described: generalized resistance and pituitary resistance. A total of 122 TR beta gene mutations have been identified thus far. A 38-year-old woman presented with intermittent palpitation. Thyroid function tests revealed elevated levels of free T4 and TSH. TSH a-subunit levels were 0.41 mlU/mL, and magnetic resonance images of the sellar region evidenced no abnormal findings. The TSH response to TRH stimulation was found to be normal. The sequence analysis of the TR beta gene verified a missense mutation in exon 11, and the observed amino acid alteration was a substitution of a valine for a methionine at codon 349. We report the first case of a woman with RTH, which was found to be caused by a missense mutation (V349M) in the TR beta gene.

Thyroid hormone resistance

Resistance to thyroid hormone (RTH) is a rare autosomal dominant inherited syndrome of reduced end-organ responsiveness to thyroid hormone. Patients with RTH have elevated serum free thyroxine (FT4) and free triiodothyronine (FT3) concentrations and normal or slightly elevated serum thyroid stimulating hormone (TSH) level. Despite a variable clinical presentation, the common characteristic clinical features are goitre but an absence of the usual symptoms and metabolic consequences of thyroid hormone excess. Patients with RTH can be classified on clinical grounds alone into either generalized resistance (GRTH), pituitary resistance (PRTH) or combined. Mutations in the thyroid hormone receptor (TR) beta gene are responsible for RTH and 122 different mutations have now been identified belonging to 300 families. With the exception of one family found to have complete deletion of the TRbeta gene, all others have been demonstrated to have minor alterations at the DNA level. The differential diagnosis includes a TSH-secreting pituitary adenoma and the presence of endogenous antibodies directed against thyroxine (T4) and triiodothyronine (T3). Failure to differentiate RTH from primary thyrotoxicosis has resulted in the inappropriate treatment of nearly one-third of patients. Although occasionally desirable, no specific treatment is available for RTH; however, the diagnosis allows appropriate genetic counselling.

[Resistance to thyroid hormone]

Resistance to thyroid hormone is a syndrome involving reduced responsiveness of target tissues to thyroid hormone. Most cases involve mutations of the thyroid hormone receptor beta gene. Since many patients demonstrate tachycardia, goiter and elevated serum thyroid hormone levels, some patients have been misdiagnosed with Graves' disease, and nearly one third of patients are being treated inappropriately. It is important to keep this diagnosis in mind when a patient with elevated thyroid hormone level accompanied by normal or slightly increased TSH levels (SITSH) is encountered. Therapy with TRIAC has been used in several patients.

Syndromes of hormone resistance in the hypothalamic-pituitary-thyroid axis

Forty years have elapsed since the first description of a syndrome of resistance in the hypothalamic-pituitary-thyroid axis, i.e., resistance to thyroid hormone action. In the last two decades many other types of resistance have been discovered, including resistance to the action of thyrotropin-releasing hormone (TRH), of thyroid-stimulating hormone (TSH), and of thyroid hormones (THs); the latter can be due not only to thyroid hormone receptor defects but also to alteration in genes encoding TH-specific transporters or components involved in metabolic pathways of THs. Moreover, alteration in genes encoding for second messengers may cause forms of resistance other than those due to receptor mutations, the most important one being that of an inactivating mutation in the G-protein alpha-subunit leading to TSH resistance in the setting of pseudohypoparathyroidism type 1a. Recognition of these rare thyroid disorders is of great importance not only for informed genetic counselling but also for avoiding diagnostic mistakes that may lead to incorrect and potentially dangerous treatments.

Difficulties in diagnosing and managing coexisting primary hypothyroidism and resistance to thyroid hormone

OBJECTIVE

To report a case of resistance to thyroid hormone compounded by autoimmune primary hypothyroidism and to discuss the unusual pattern of results of thyroid function tests.

METHODS

A clinical case history is presented and illustrated with laboratory findings. The difficulty of monitoring the patient's response to levothyroxine supplement is also discussed, and relevant issues are addressed, including reviews of the literature.

RESULTS

A 45-year-old woman presented with longstanding and nonspecific symptoms of general anxiety and lethargy. Clinically, she was assessed to be euthyroid with no goiter. Her thyrotropin (thyroid-stimulating hormone or TSH) level was 43.6 (1/4)IU/mL, free thyroxine was 27.6 pmol/L, and free triiodothyronine was 7.8 pmol/L. Her anti-thyroid peroxidase titer was 1:102,400. Primary hypothyroidism was diagnosed, and treatment with 50 (1/4)g of levothyroxine daily was initiated, with progressive dose escalation. The patient, however, had thyrotoxic symptoms when her TSH was rendered "normal." The patient then discontinued her levothyroxine therapy, with a consequent elevation of her TSH level to 170.8 (1/4)IU/mL in conjunction with severe lethargy and lassitude. Biochemical evidence of metabolic disturbances was also present at the time, with hypercholesterolemia and elevated creatine kinase concentration. Rechallenge with levothyroxine resulted in considerable improvement in her biochemical findings and symptoms.

CONCLUSION

This patient has an interesting combination of autoimmune primary hypothyroidism and resistance to thyroid hormone. Levothyroxine replacement therapy was complicated by the nonspecificity of symptoms and the lack of an established TSH target value in this condition. Consideration should be given to using the affected family members' mean TSH level, when available, as a target guide for replacement therapy.