Long-Term Carbimazole Treatment of Neonatal Nonautoimmune Hyperthyroidism due to a New Activating TSH Receptor Gene Mutation (Ala428Val)

Central TSH Dysregulation in a Patient with Familial Non-Autoimmune Autosomal Dominant Hyperthyroidism Due to a Novel Thyroid-Stimulating Hormone Receptor Disease-Causing Variant

Background and Objectives. Familial non-autoimmune autosomal dominant hyperthyroidism (FNAH) is a rare cause of childhood hyperthyroidism. It is caused by the thyroid-stimulating hormone receptor (TSHR) gene variants. So far, only around 40 families with FNAH have been reported. Patients with activating TSHR variants demonstrated the same classical signs and symptoms of hyperthyroidism as seen in patients with Graves' disease. Since 2012, ablative therapy is recommended to avoid relapses of hyperthyroidism and its consequences. Case Presentation. We presented a young adult male patient with a novel heterozygous TSHR disease-causing variant p.Arg418Lys (c.1253G>A) in the exon 10, who presented with a mild but progressive FNAH, with a follow-up since infancy. Discussion. Constantly suppressed TSH, including during the euthyreosis in childhood and hypothyreosis after iodine ablation therapy, suggested central dysregulation of the TSH secretion.

Nonautoimmune congenital hyperthyroidism due to p.Asp633Glu mutation in the TSHR gene

Most cases of congenital hyperthyroidism are autoimmune forms caused by maternal thyroid stimulating antibodies. Nonautoimmune forms of congenital hyperthyroidism caused by activating mutations of the thyrotropin receptor (TSHR) gene are rare. A woman gave birth to a boy during an emergency cesarean section at 33 weeks of gestation due to fetal tachycardia. On the 24th day of life, thyroid function tests were performed due to persistent tachycardia, and hyperthyroidism was confirmed. Auto-antibodies to TSHR, thyroid peroxidase, and thyroglobulin were not found. The patient was treated with propylthiouracil and propranolol, but hyperthyroidism was not well controlled. At 3 months of age, the patient had craniosynostosis and hydrocephalus, and underwent a ventriculoperitoneal shunt operation. Direct sequencing of the TSHR gene showed a heterozygous mutation of c.1899C>A (p.Asp633Glu) in exon 10. No mutations were discovered in any of the parents in a familial genetic study. We have reported a case of sporadic nonautoimmune congenital hyperthyroidism, by a missense mutation of the TSHR gene, for the first time in South Korea.

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.

Sporadic nonautoimmune neonatal hyperthyroidism due to A623V germline mutation in the thyrotropin receptor gene

Neonatal hyperthyroidism is a rare disorder and occurs in two forms. An autoimmune form is associated with maternal Graves' disease, resulting from transplacental passage of maternal thyroid-stimulating antibodies and a nonautoimmune form is caused by gain of function mutations in the thyrotropin receptor (TSHR) gene. Thyrotoxicosis caused by germline mutations in the TSHR gene may lead to a variety of clinical consequences. To date, 55 activating mutations of the TSHR gene have been documented. Fourteen cases with sporadic activating TSHR germline mutations have been described. Here we report a male infant with nonautoimmune hyperthyroidism due to an activating germline TSHR mutation (A623V), whose clinical picture started in the newborn period with severe hyperthyroidism. His parents did not have the same mutation. This mutation had been previously detected as a somatic mutation in patients with toxic adenomas. This is the first report of a sporadic case of nonautoimmune congenital hyperthyroidism associated with A623V mutation.

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.

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 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.

A new silent germline mutation of the TSH receptor: coexpression in a hyperthyroid family member with a second activating somatic mutation

BACKGROUND

Up to date, three thyroid-stimulating hormone receptor (TSHR) germline variants have been reported for which no functional consequences have been detected by in vitro characterizations. However, familial nonautoimmune hyperthyroidism and hot nodules are clearly associated with constitutively activating TSHR germline mutations. We describe a family with a new TSHR germline mutation that is associated with euthyroidism in 13 family members and hyperthyroidism in 1 family member.

METHODS

Mutation analysis of the TSHR gene was performed by denaturing gradient gel electrophoresis. TSHR constructs were characterized by determination of cell surface expression, 3'-5'-cyclic adenosine monophosphate (cAMP) accumulation, and constitutive cAMP activity.

RESULTS

A novel TSHR germline mutation (N372T) was found in a man who presented with thyrotoxicosis. The mutation was also detected in 13 family members, all of whom were euthyroid. Interestingly, an additional constitutively active somatic mutation (S281N) was identified on the second parental TSHR allele of the hyperthyroid index patient. Linear regression analysis showed a lack of constitutive activity for N372T. Moreover, coexpression studies of N372T with S281N did not reveal any evidence for a functional influence of N372T on the constitutively active mutation (CAM).

CONCLUSIONS

N372T is unlikely to cause altered thyroid function. This is consistent with the finding that only the index patient with the additional somatic mutation S281N was hyperthyroid.

Pharmacogenomic and Structural Analysis of Constitutive G Protein–Coupled Receptor Activity

G protein-coupled receptors (GPCRs) respond to a chemically diverse plethora of signal transduction molecules. The notion that GPCRs also signal without an external chemical trigger, i.e., in a constitutive or spontaneous manner, resulted in a paradigm shift in the field of GPCR pharmacology. The discovery of constitutive GPCR activity and the fact that GPCR binding and signaling can be strongly affected by a single point mutation drew attention to the evolving area of GPCR pharmacogenomics. For a variety of GPCRs, point mutations have been convincingly linked to human disease. Mutations within conserved motifs, known to be involved in GPCR activation, might explain the properties of some naturally occurring, constitutively active GPCR variants linked to disease. In this review, we provide a brief historical introduction to the concept of constitutive receptor activity and the pharmacogenomic and structural aspects of constitutive receptor activity.

Subclinical hyperthyroidism due to a thyrotropin receptor (TSHR) gene mutation (S505R)

AIM

To identify the molecular defect by which non-autoimmune subclinical hyperthyroidism was caused in a 6-mo-old infant who presented with weight loss.

METHODS

Congenital non-autoimmune hyperthyroidism is caused by activating germline mutations in the thyrotropin receptor (TSHR) gene. Therefore, the TSHR gene was sequenced directly from the patient's genomic DNA.

RESULTS

Molecular analysis revealed a heterozygous point mutation (S505R) in the TSHR gene as the underlying defect.

CONCLUSION

A constitutively activating mutation in the TSHR gene has to be considered not only in patients with severe congenital non-autoimmune hyperthyroidism, but also in children with subclinical non-autoimmune hyperthyroidism.