A novel activating mutation in transmembrane helix 6 of the thyrotropin receptor as cause of hereditary nonautoimmune hyperthyroidism

Novel presentation of the c.1856A > G (p.Asp619Gly) TSHR gene-activating variant: relapsing hyperthyroidism in three subsequent generations manifesting in early childhood and an in vitro functional study

BACKGROUND

Familial non-autoimmune hyperthyroidism is a rare disease caused by germline activating variants in the thyroid-stimulating hormone receptor (TSHR) gene. The c.1856A > G (p.Asp619Gly) pathogenic variant has been described in cases of toxic adenoma but never before, to our knowledge, in a case of familial non-autoimmune hyperthyroidism.

PATIENT FINDINGS

A 3-year-old boy was admitted for acute gastroenteritis presenting with goiter and tall stature. Laboratory findings revealed peripheral hyperthyroidism and negativity for thyroid autoantibodies. Antithyroid drug treatment was effective, but relapses occurred shortly after attempts to decrease the drug dose. As the boy's father and paternal grandmother also experienced relapsing hyperthyroidism manifesting in early childhood, genetic testing of TSHR was indicated. The c.1856A > G (p.Asp619Gly) pathogenic variant was found in all three affected family members. Functional in vitro characterization of the variant verified that it enhances constitutional activation of the receptor, leading to increased production of cyclic adenosine monophosphate. Total thyroidectomy was indicated in the boy due to an unsatisfactory prognosis. Due to persistent positive thyroglobulin serum concentration, a diagnostic radioiodine scan was performed approximately 2 years later. Residual thyroid tissue was revealed; therefore, radioiodine ablative therapy was performed. Despite adequate thyroxine substitution over a long period of follow-up, TSH remained suppressed.

CONCLUSIONS

Unlike Graves' disease, familial non-autoimmune hyperthyroidism cases present with antithyroid drug-dependence. Not ultrasound but positive thyroglobulin serum concentration indicated residual thyroid tissue. Early detection of residual thyroid tissue and radioiodine ablation prevented the subject from experiencing relapsing hyperthyroidism and undergoing unnecessary repeated surgery. Life-long hormone substitution should be adjusted to free thyroxine rather than TSH serum concentrations.

Hyperthyroidism and Papillary Thyroid Carcinoma in Thyrotropin Receptor D633H Mutant Mice

BACKGROUND

Constitutively active thyrotropin receptor (TSHR) mutations are the most common etiology of non-autoimmune hyperthyroidism (NAH). Thus far, the functionality of these mutations has been tested in vitro, but the in vivo models are lacking.

METHODS

To understand the pathophysiology of NAH, the patient-derived constitutively active TSHR D633H mutation was introduced into the murine Tshr by homologous recombination.

RESULTS

In this model, both subclinical and overt hyperthyroidism was observed, depending on the age, sex, and genotype. Homozygous mice presented hyperthyroidism at two months of age, while heterozygous animals showed only suppressed thyrotropin. Interestingly, at six months of age, thyroid hormone concentrations in all mutant mice were analogous to wild-type mice, and they showed colloid goiter with flattened thyrocytes. Strikingly, at one year of age, nearly all homozygous mice presented large papillary thyroid carcinomas. Mechanistically, this papillary thyroid carcinoma phenotype was associated with an overactive thyroid and strongly increased stainings of proliferation-, pERK-, and NKX2-1 markers, but no mutations in the "hot-spot" areas of common oncogenes (Braf, Nras, and Kras) were found.

CONCLUSIONS

This is the first study to reveal the dynamic age-, sex-, and genotype-dependent development of NAH. Furthermore, the study shows that a constitutively active TSHR can trigger a malignant transformation of thyrocytes.

Inheritable and sporadic non-autoimmune hyperthyroidism

Hyperthyroidism is a clinical state that results from high thyroid hormone levels which has multiple etiologies, manifestations, and potential therapies. Excluding the autoimmune Graves disease, autonomic adenomas account for the most import cause of non-autoimmune hyperthyroidism. Activating germline mutations of the TSH receptor are rare etiologies for hyperthyroidism. They can be inherited in an autosomal dominant manner (familial or hereditary, FNAH), or may occur sporadically as a de novo condition, also called: persistent sporadic congenital non-autoimmune hyperthyroidism (PSNAH). These three conditions: autonomic adenoma, FNAH and PSNAH constitute the inheritable and sporadic non-autoimmune hyperthyroidism. Particularities in epidemiology, etiology, molecular and clinical aspects of these three entities will be discussed in this review in order to guide to an accurate diagnosis allowing among others genetic counseling and presymptomatic diagnosis for the affected families. The optimal treatment based on the right diagnosis will avoid consequences of a persistent or relapsing hyperthyroidism.

A Japanese family with nonautoimmune hyperthyroidism caused by a novel heterozygous thyrotropin receptor gene mutation

BACKGROUND

Hyperthyroidism caused by activating mutations of the thyrotropin receptor gene (TSHR) is rare in the pediatric population.

METHODS

We found a Japanese family with hyperthyroidism without autoantibody. DNA sequence analysis of TSHR was undertaken in this family. The functional consequences for the Gs-adenylyl cyclase and Gq/11-phospholipase C signaling pathways and cell surface expression of receptors were determined in vitro using transiently transfected human embryonic kidney 293 cells.

RESULTS

We identified a heterozygous mutation (M453R) in exon 10 of TSHR. In this family, this mutation was found in all individuals who exhibited hyperthyroidism. The results showed that this mutation resulted in constitutive activation of the Gs-adenylyl cyclase system. However, this mutation also caused a reduction in the activation capacity of the Gq/11-phospholipase C pathway, compared with the wild type.

CONCLUSION

We demonstrate that the M453R mutation is the cause of nonautoimmune hyperthyroidism.

Prevalence of thyrotropin receptor germline mutations and clinical courses in 89 hyperthyroid patients with diffuse goiter and negative anti-thyrotropin receptor antibodies

BACKGROUND

We studied the frequency of thyrotropin (TSH) receptor mutations in hyperthyroid patients with diffuse goiter and negative TSH receptor antibodies (TRAb), and the clinical pictures of the hyperthyroid patients in the presence and absence of mutations.

PATIENTS AND METHODS

From 2003 through 2012, 89 hyperthyroid patients with diffuse goiter and negative TRAb based on a second- or third-generation assay underwent sequence analysis of the TSH receptor gene from peripheral leukocytes. The outcome of hyperthyroidism in patients with a TSH receptor mutation and their affected family members was compared with that in patients without any mutation after a 1-10-year follow-up.

RESULTS

Germline mutations of the TSH receptor occurred in 4 of the 89 patients (4.5%), including 3 definitive constitutively activating mutations (L512Q, E575K, and D617Y). The main difference in the clinical outcome of hyperthyroidism was that no patients with a TSH receptor mutation achieved euthyroidism throughout the follow-up, while 23.5% of patients without any mutation entered remission. The progression from subclinical to overt hyperthyroidism was not significantly different between patients with or without a mutation. Meanwhile, 10.3% of TRAb-negative patients without any TSH receptor mutation developed TRAb-positive Graves' hyperthyroidism during the follow-up.

CONCLUSIONS

The prevalence of nonautoimmune hyperthyroidism with TSH receptor mutations is lower than that of latent Graves' disease in TRAb-negative patients with hyperthyroidism. However, all affected patients with a TSH receptor mutation showed persistent hyperthyroidism regardless of subclinical or overt hyperthyroidism throughout the follow-up.

2012 European thyroid association guidelines for the management of familial and persistent sporadic non-autoimmune hyperthyroidism caused by thyroid-stimulating hormone receptor germline mutations

All cases of familial thyrotoxicosis with absence of evidence of autoimmunity and all children with persistent isolated neonatal hyperthyroidism should be evaluated for familial non-autoimmune autosomal dominant hyperthyroidism (FNAH) or persistent sporadic non-autoimmune hyperthyroidism (PSNAH). First, all index patients should be analysed for the presence/absence of a thyroid-stimulating hormone (TSH) receptor (TSHR) germline mutation, and if they display a TSHR germline mutation, all other family members including asymptomatic and euthyroid family members should also be analysed. A functional characterization of all new TSHR mutations is necessary. Appropriate ablative therapy is recommended to avoid relapses of hyperthyroidism and its consequences, especially in children. Therefore, in children the diagnosis of FNAH or PSNAH needs to be established as early as possible in the presence of the clinical hallmarks of the disease.

Shared sporadic and somatic thyrotropin receptor mutations display more active in vitro activities than familial thyrotropin receptor mutations

BACKGROUND

Germline thyrotropin receptor (TSHR) mutations are associated with sporadic congenital nonautoimmune hyperthyroidism and familial nonautoimmune hyperthyroidism. Somatic TSHR mutations are associated with toxic thyroid nodules (TTNs). The objective of the study was to define a relation of the clinical appearance and the in vitro activity (IVA) of the TSHR mutations described by several authors for these thyroid disorders.

METHODS

We analyzed the IVAs published as linear regression analysis (LRA) of the constitutive activity as a function of the TSHR expression and the basal cyclic adenosine monophosphate (cAMP) values to determine differences between exclusively somatic, exclusively familial, and shared sporadic and somatic TSHR-mutations. Further, we investigated correlations of the LRAs/basal cAMP values with clinical activity characteristics (CACs) of TTNs, such as largest diameter of the TTN and the age of the patient at thyroid surgery.

RESULTS

Shared sporadic and somatic mutations showed higher median LRA (14.5) and higher median basal cAMP values (fivefold) than exclusively familial mutations (6.1, p = 0.0002; 2.9-fold, p < 0.0001, respectively). Moreover, mutations shared between sporadic congenital nonautoimmune hyperthyroidism and toxic thyroid nodules (TTNs) showed higher median LRA/basal cAMP values (p < 0.0001) than exclusively somatic mutations in TTNs (5.1; 3.89-fold, respectively). Exclusively somatic mutations and exclusively familial mutations showed no significant difference in their median LRA values (p = 0.786) but a significant difference for basal cAMP values (p = 0.0006). The two examined CACs showed no correlation with the IVA characterized by LRA/basal cAMP values or with the presence or absence of a TSHR-mutation.

CONCLUSIONS

This systematic analysis of published constitutively activating TSHR-mutations, their CACs, and their IVA provides evidence for higher IVA of shared sporadic and somatic TSHR mutations as compared with familial TSHR mutations. CACs of somatic TSHR mutations in TTNs did not have a clear association with the IVA as characterized by LRA or basal cAMP values.

Genetic hyperthyroidism: hyperthyroidism due to activating TSHR mutations

Three syndromes affecting the thyroid gland are described in the literature separately: familial nonautoimmune hyperthyroidism, sporadic congenital nonautoimmune hyperthyroidism, and autonomous adenomas. Recent studies have shown that these three syndromes are caused by similar activating mutations of the TSH receptor gene (TSHR), and that the consequences of these mutations on the physiology and gene expression of the thyroid are qualitatively, but not quantitatively, similar. The three syndromes and two suggested unrecognized variants are in fact facets of the same disease, genetic hyperthyroidism due to TSHR mutations, the expression of which depends on the intensity of activation, its timing, and on the number of affected cells.

Subclinical nonautoimmune hyperthyroidism in a family segregates with a thyrotropin receptor mutation with weakly increased constitutive activity

BACKGROUND

Subclinical hyperthyroidism is usually associated with Graves' disease or toxic nodular goiter. Here we report a family with hereditary subclinical hyperthyroidism caused by a constitutively activating germline mutation of the thyrotropin receptor (TSHR) gene.

METHODS

The proband was a 64-year-old Japanese woman who presented with a thyroid nodule and was found to be euthyroid with a suppressed serum TSH. The nodule was not hot. Although antibodies to thyroid peroxidase and thyroglobulin antibodies were present, TSHR antibodies were not detected by TSH-binding inhibition or by bioassay. Two of her middle-aged sons, but not her daughter, also had subclinical hyperthyroidism without TSHR antibodies. Without therapy, the clinical condition of the affected individuals remained unchanged over 3 years without development of overt hyperthyroidism.

RESULTS

A novel heterozygous TSHR point mutation causing a glutamic acid to lysine substitution at codon 575 (E575K) in the second extracellular loop was detected in the three family members with subclinical hyperthyroidism, but was absent in her one daughter with normal thyroid function. In vitro functional studies of the E575K TSHR mutation demonstrated a weak, but significant, increase in constitutive activation of the cAMP pathway.

CONCLUSION

Although hereditary nonautoimmune overt hyperthyroidism is very rare, TSHR activating mutations as a cause of subclinical hyperthyroidism may be more common and should be considered in the differential diagnosis, especially if familial.

Lack of consistent association of thyrotropin receptor mutations in vitro activity with the clinical course of patients with sporadic non-autoimmune hyperthyroidism

BACKGROUND

Up to date, 14 patients with sporadic non-autoimmune hyperthyroidism (SNAH) caused by sporadic germline mutations in the TSH receptor (TSHR) gene have been reported. Despite considerable differences in the activity of hyperthyroidism, all SNAH case reports concluded that the demonstrated constitutive activity explains the phenotype.

AIM

Recently, linear regression analysis (LRA) of constitutive activity as a function of TSHR expression determined by 125I-bTSH binding or fluorescence activated cell sorting analysis was described as a more reliable way of characterizing the in vitro activity (IVA) of a constitutively activating TSHR mutation. Therefore, we analyzed a possible genotype-phenotype correlation in a systematic review of the case reports and investigated the TSHR mutation's LRA in selected cases.

MATERIAL AND METHODS

We determined the LRA for all sporadic germline mutations which had not previously been reported. Moreover, we systematically evaluated all case reports of SNAH for evidence of an association of the clinical course (CC) with the IVA of the mutated TSHR.

RESULTS

The LRA determined were: M453T (5.2+/-0.8), L512Q (4.5+/-0.7), I568T (25.6+/-6.3), F631L (45.9+/-9.4), T632I (14.5+/-2.7), D633Y (16.4+/-6.4). None of the 10 examined clinical signs showed a significant association with the LRA. Moreover, the comparison of the CC of patients harboring the same mutation (S281N, M453T, I568T, S505N) also showed no relation of the clinical activity with a high LRA.

CONCLUSION

Considering the different diagnostic circumstances, therapeutic strategies and the limitations of a systematic analysis of case reports due to the restricted number of case reports and limited follow-up we found no consistent relation of the TSHR mutation's IVA determined by LRA with the CC of patients with SNAH. This may also be due to the action of genetic, epigenetic, and environmental modifiers.

Hyperthyroidism caused by a germline activating mutation of the thyrotropin receptor gene: difficulties in diagnosis and therapy

BACKGROUND

Germline activating mutations of the thyrotropin receptor (TSHR) gene have been considered as the only known cause of sporadic nonautoimmune hyperthyroidism in the pediatric population. Here we describe the long-term follow-up and evaluation of a patient with sporadic nonautoimmune primary hyperthyroidism who was found to have a de novo germline activating mutation of the TSHR gene.

SUMMARY

The patient was an infant who presented at the age of 10 months in an unconscious state with exsiccation, wet skin, fever, and tachycardia. Nonautoimmune primary hyperthyroidism was diagnosed, and brain magnetic resonance imaging and computed tomography showed also Arnold-Chiari malformation type I. Continuous propylthiouracil treatment resulted in a prolonged clinical cure lasting for 10 years. At the age of 11 years and 5 months the patient underwent subtotal thyroidectomy because of symptoms of trachea compression caused by a progressive multinodular goiter. However, 2 months after surgery, hormonal evaluation indicated recurrent hyperthyroidism and the patient was treated with propylthiouracil during the next 4 years. At the age of 15 years the patient again developed symptoms of trachea compression. Radioiodine treatment resulted in a regression of the recurrent goiter and a permanent cure of hyperthyroidism without relapse during the last 3 years of his follow-up. Sequencing of exon 10 of the TSHR gene showed a de novo heterozygous germline I630L mutation, which has been previously described as activating mutation at somatic level in toxic thyroid nodules.

CONCLUSIONS

The I630L mutation of the TSHR gene occurs not only at somatic level in toxic thyroid nodules, but also its presence in germline is associated with nonautoimmune primary hyperthyroidism. Our case report demonstrates that in this disorder a continuous growth of the thyroid occurs without any evidence of elevated TSH due to antithyroid drug overdosing. This may justify previous recommendations for early treatment of affected patients with removal of as much thyroid tissue as possible.

Thyroid gene expression in familial nonautoimmune hyperthyroidism shows common characteristics with hyperfunctioning autonomous adenomas

CONTEXT

Dominant activating mutations of the TSH receptor are the cause of familial nonautoimmune hyperthyroidism (FNAH) (inherited mutations affecting the whole gland since embryogenesis) and the majority of hyperfunctioning autonomous adenomas (AAs) (somatic mutations affecting only one cell later in the adulthood).

OBJECTIVE

The objective of the study was defining the functional and molecular phenotypes of FNAH and comparing them with the ones of AA.

DESIGN

Functional phenotypes were determined in vitro and molecular phenotypes by hybridization on microarray slides.

PATIENTS

Nine patients with FNAH were investigated, six for functional in vitro study of the tissue and five for gene expression.

RESULTS

Iodide metabolism, H(2)O(2), cAMP, and inositol phosphate generation in FNAH slices stimulated or not with TSH were normal. The mitogenic response of cultured FNAH thyrocytes to TSH was normal but more sensitive to the hormone. Gene expression profiles of FNAH and AAs showed that among 474 genes significantly regulated in FNAH, 93% were similarly regulated in AAs. Besides, 783 genes were regulated only in AAs. Bioinformatic analysis pointed out common down-regulations of genes involved in immune response, cell/cell and cell/matrix adhesions, and apoptosis. Pathways up-regulated only in AAs mainly involve diverse biosyntheses. These results are consonant with the larger growth of AAs than FNAH tissues.

CONCLUSIONS

Whether hereditary or somatic after birth, activating mutations of the TSH receptor have the same qualitative consequences on the thyroid cell phenotype, but somatic mutations in AAs have a much stronger effect than FNAH mutations. Both are variants of one disease: genetic hyperthyroidism.

The superagonistic activity of bovine thyroid-stimulating hormone (TSH) and the human TR1401 TSH analog is determined by specific amino acids in the hinge region of the human TSH receptor

Bovine TSH (bTSH) has a higher affinity to the human TSHR (hTSHR) and a higher signaling activity than human TSH (hTSH). The molecular reasons for these phenomena are unknown. Distinct negatively charged residues (Glu297, Glu303, and Asp382) in the hinge region of the hTSHR are known to be important for bTSH binding and signaling. To investigate the potential relevance of these positions for differences between bTSH and hTSH in the interaction to the hTSHR, we determined bTSH- and hTSH-mediated cAMP production of several substitutions at these three hinge residues. To examine specific variations of hTSH, we also investigated the superagonistic hTSH analog TR1401 (TR1401), whose sequence differs from hTSH by four additional positively charged amino acids that are also present in bTSH. To characterize possible interactions between the acidic hTSHR positions Glu297, Glu303, or Asp382 and the additional basic residues of TR1401, we investigated TR1401 binding and signaling properties. Our data reveal increased cAMP signaling of the hTSHR using TR1401 and bTSH compared with hTSH. Whereas Asp382 seems to be important for bTSH- and TR1401-mediated but not for hTSH-mediated signaling, the substitution E297K exhibits a decreased signaling for all three TSH variants. Interestingly, bTSH and TR1401 showed only a slightly different binding pattern. These observations imply that specific residues of the hinge region are mediators of the superagonistic activity of bTSH and TR1401 in contrast to hTSH. Moreover, the simultaneous localization of binding components in the glycoprotein hormone molecule and the receptor hinge region permits important reevaluation of interacting hormone receptor domains.

Expanding clinical spectrum of non-autoimmune hyperthyroidism due to an activating germline mutation, p.M453T, in the thyrotropin receptor gene

OBJECTIVE

To describe clinical and genetic features of a Thai family with non-autoimmune hyperthyroidism (NAH) caused by an activating germline mutation in the thyrotropin receptor (TSHR) gene.

PATIENTS

Three affected individuals from the same family (a father and his two children) were studied. Clinical and imaging findings were reviewed and compared. GENETIC ANALYSIS: Genomic DNA was extracted from peripheral blood leukocytes and mutation analysis of the entire coding sequence of the TSHR gene was performed in both children and their parents by direct DNA sequencing.

RESULTS

A heterozygous germline T to C transition in exon 10 of the TSHR gene (c.1358T-->C) resulting in the substitution of methionine (ATG) by threonine (ACG) at codon 453 (p.M453T) was identified in the father and his two children. They presented with different clinical severity and variable age of onset. In addition to hyperthyroidism, ventriculomegaly and bilateral shortening of the fifth metacarpal bones and the middle phalanges of the fifth fingers were consistently found in all affected individuals.

CONCLUSIONS

Ventriculomegaly and bilateral shortening of the fifth metacarpal bones and the middle phalanges of the fifth fingers might be characteristic features of NAH because of an activating TSHR germline mutation. In addition, the shortening of the middle phalanges of the fifth fingers has never been previously described, expanding the phenotypic spectrum of the disease.

A somatic gain-of-function mutation in the thyrotropin receptor gene producing a toxic adenoma in an infant

BACKGROUND

Activating mutations of the thyroid stimulating hormone receptor gene (TSHR) are rare in the neonate and in the pediatric population. They are usually present in the germline, and are either inherited or occur de novo. Somatic mutations in TSHR are unusual in the pediatric population.

METHODS

We describe a nine-month-old infant with thyrotoxicosis who harbored an activating somatic mutation in TSHR that was not present in the germline.

RESULTS

As genomic DNA analysis failed to show a TSHR gene mutation, a radioiodide scan was performed to reveal a unilateral localization of uptake suppressing the remaining thyroid tissue. Genomic and complementary DNA analyses of the active thyroid tissue, removed surgically, identified a missense mutation (D633Y) located in the sixth transmembrane domain of the TSHR. The absence of this TSHR mutation in circulating mononuclear cells and in unaffected thyroid tissue confirmed the somatic nature of this genetic alteration.

CONCLUSIONS

To the authors' knowledge, this is the youngest patient to receive definitive treatment for hyperthyroidism due to an activating mutation of TSHR.

A family with a novel TSH receptor activating germline mutation (p.Ala485Val)

Autosomal dominant nonautoimmune hyperthyroidism (ADNAH) is caused by gain of function mutations in the TSH receptor (TSHr) gene and characterized by toxic thyroid hyperplasia with a variable age of onset in the absence of thyroid antibodies and clinical symptoms of autoimmune thyroid disease in at least two generations. We report here a Turkish family with a novel TSHr gene mutation with distinct features all consistent with ADNAH. Thyroid function tests of the proband were as follows: free T3: 13.1 pg/ml (N: 1.8-4.6); free T4: 5.1 ng/dl (N: 0.9-1.7); TSH: 0.01 microIU/ml (N: 0.2-4.2); and TSH receptor antibody: 2 IU/ml (N: 0-10). A heterozygous missense mutation in exon 10 of the TSHr gene (c.1454C>T) resulting in the substitution of valine for alanine at codon 485 (p.Ala485Val) was found in the father and his son and daughter. This mutation had arisen de novo in the father. Functional studies of the novel TSHr germline mutation demonstrated a higher constitutive activation of adenyl cyclase than wild type without any effect on phospholipase C activity. In conclusion, our data indicate that gain of function germline mutations in the TSHr gene should be investigated in families with members suffering from thyrotoxicosis and progressive growth of goiter, but without clinical and biochemical evidence of autoimmune thyroid disease. In addition, patients harboring the same mutation of the TSHr gene may show wide phenotypic variability with respect to the age at onset, and severity of hyperthyroidism and thyroid growth.

TSH signalling and cancer

Thyroid cancers are the most frequent endocrine neoplasms and mutations in the thyrotropin receptor (TSHR) are unusually frequent. Here we present the state-of-the-art concerning the role of TSHR in thyroid cancer and discuss it in light of the cancer stem cell theory or the classical view. We briefly review the gene and protein structure updating the cancer related TSHR mutations database. Intriguingly, hyperfunctioning TSHR mutants characterise differentiated cancers in contrast to undifferentiated thyroid cancers which very often bear silenced TSHR. It remains unclear whether TSHR alterations in thyroid cancers play a role in the onset or they appear as a consequence of genetic instability during evolution, but the presence of functional TSHR is exploited in therapy. We outline the signalling network build up in the thyrocyte between TSHR/PKA and other proliferative pathways such as Wnt, PI3K and MAPK. This networks integrity surely plays a role in the onset/evolution of thyroid cancer and needs further research. Lastly, future investigation of epigenetic events occurring at the TSHR and other loci may give better clues for molecular based therapy of undifferentiated thyroid carcinomas. Targeted demethylating agents, histone deacetylase inhibitors combined with retinoids and specific RNAis may help treatment in the future.

Congenital neonatal hyperthyroidism caused by germline mutations in the TSH receptor gene

Neonatal hyperthyroidism, a rare and serious disorder, occurs in two forms. An autoimmune form associated with maternal Graves' disease, resulting from transplacental passage of maternal thyroid-stimulating antibodies, and a non-autoimmune form, resulting from mutations in the stimulatory G protein or the thyrotropin receptor (TSHR) causing constitutive activation of intracellular signaling cascades. To date, 29 separate cases of thyrotoxicosis caused by germline mutations of the TSHR have been documented. These cases have expressed themselves in a range of clinical consequences. This report describes a new case of a newborn with non-autoimmune hyperthyroidism secondary to a constitutively active TSHR mutation (S281N) whose clinical course was complicated by severe respiratory compromise. Typical clinical findings in this disorder are discussed by a review of all previously published cases.

A novel thyrotropin receptor germline mutation (Asp617Tyr) causing hereditary hyperthyroidism

Constitutively activating germline mutations of the thyrotropin receptor (TSHR) gene have been identified as a molecular cause of hereditary nonautoimmune hyperthyroidism. We describe here a Japanese kindred with two affected individuals who showed overt hyperthyroidism and mild goiter in the absence of TSHR antibodies. A novel heterozygous germline point mutation, identified in both individuals, resulted in an amino acid substitution of aspartic acid for tyrosine at codon 617 (Asp617Tyr) in the third intracellular loop of the TSHR. Screening of 7 additional family members led to the identification of the same mutation in 4 relatives: 1 had undergone thyroidectomy due to hyperthyroidism but 3 were asymptomatic with subclinical hyperthyroidism. In vitro functional studies of the Asp617Tyr TSHR demonstrated a constitutive activation of the cyclic adenosine monophosphate pathway, but not of the inositol phosphate cascade, with data similar to those of Asp619Gly, the first constitutively activating mutant TSHR identified. Treatment with inorganic iodine for 7 months successfully relieved all symptoms of hyperthyroidism in both patients.

A new case of familial nonautoimmune hyperthyroidism caused by the M463V mutation in the TSH receptor with anticipation of the disease across generations: a possible role of iodine supplementation

OBJECTIVE

Hereditary (familial) nonautoimmune hyperthyroidism (FNAH) is caused by activating thyroid-stimulating hormone (thyrotropin) receptor (TSHR) germline mutations. We describe a family with recurrent thyrotoxicosis and goiter across three generations, including an 8-year-old girl.

MAIN OUTCOME

Sequences of the TSHR gene in the index patient, her father, her paternal grandmother, and a paternal uncle demonstrated the presence of an identical germline TSHR mutation. The mutation was heterozygous and determined the substitution of valine for methionine (codon 463; ATG-->GTG) in the second transmembrane domain of the TSHR in all the affected patients, but in none of the unaffected family members.

CONCLUSIONS

We compared the clinical presentation of FNAH in the family reported by us with the other cases harboring the same mutation reported in the literature. This analysis revealed high variability in the phenotypical expression of the disease. In the family reported by us, we also observed a clear anticipation of the onset of the disease across generations, and we discussed whether such a phenomenon can be the consequence of the increased iodine supplementation in the area where the family lives.