Aggressive metastatic follicular thyroid carcinoma with anaplastic transformation arising from a long-standing goiter in a patient with Pendred's syndrome

Primary Central Nervous System Lymphoma (PCNSL) Following Thyroid Cancer Surgery: A Case Report of Misdiagnosed Brain Metastasis and Literature Review

Objectives: This article reports a rare case of primary central nervous system lymphoma (PCNSL) found in a patient with thyroid cancer after surgery.

METHODS

The patient was initially misdiagnosed with brain metastases, and the diagnosis of PCNSL was later confirmed by pathology.

RESULTS

The analysis of this case and review of the relevant literature explores the possible mechanisms of the coexistence of thyroid cancer and PCNSL, as well as their diagnostic, differential diagnostic, and therapeutic challenges.

CONCLUSIONS

The article suggests a possible correlation between the coexistence of multiple cancers and autoimmune diseases and emphasizes that disease cannot be only considered in a monolithic way.

Knowns and unknowns about congenital hypothyroidism: 2022 update

Several excellent guidelines and expert opinions on congenital hypothyroidism (CH) are currently available. Nonetheless, these guidelines do not address several issues related to CH in detail. In this review, the authors chose the following seven clinical issues that they felt were especially deserving of closer scrutiny in the hope that drawing attention to them through discussion would help pediatric endocrinologists and promote further interest in the treatment of CH. 1. How high should the levothyroxine (L-T4) dose be for initial treatment of severe and permanent CH? 2. What is the optimal method for monitoring treatment of severe CH? 3. At what level does maternal iodine intake during pregnancy affect fetal and neonatal thyroid function? 4. Does serum thyroglobulin differ between patients with a dual oxidase 2 (DUOX2) variants and those with excess iodine? 5. Who qualifies for a genetic diagnosis? 6. What is the best index for distinguishing transient and permanent CH? 7. Is there any cancer risk associated with CH? The authors discussed these topics and jointly edited the manuscript to improve the understanding of CH and related issues.

Genetic susceptibility to hereditary non-medullary thyroid cancer

Non-medullary thyroid cancer (NMTC) is the most common type of thyroid cancer. With the increasing incidence of NMTC in recent years, the familial form of the disease has also become more common than previously reported, accounting for 5-15% of NMTC cases. Familial NMTC is further classified as non-syndromic and the less common syndromic FNMTC. Although syndromic NMTC has well-known genetic risk factors, the gene(s) responsible for the vast majority of non-syndromic FNMTC cases are yet to be identified. To date, several candidate genes have been identified as susceptibility genes in hereditary NMTC. This review summarizes genetic predisposition to non-medullary thyroid cancer and expands on the role of genetic variants in thyroid cancer tumorigenesis and the level of penetrance of NMTC-susceptibility genes.

Follicular thyroid cancer in a patient with Pendred syndrome

We present the clinical and molecular studies of a family with Pendred syndrome, in which one affected individual developed follicular thyroid cancer. Two siblings with classic Pendred syndrome triad were operated on because of enormous multinodular goiter. Histopathology showed a follicular thyroid cancer in the male and a multinodular goiter in the female. PDS gene analysis revealed G-to-A transition in the splice donor site of intron 8 (IVS8+1G>A/c.1001+1G>A). Careful surveillance is needed in all cases of thyroid nodules in patients with Pendred syndrome, due to the high risk of malignancy.

Genetics of primary congenital hypothyroidism-a review

PURPOSE

Congenital primary hypothyroidism (CH) is a state of inadequate thyroid hormone production detected at birth, caused either by absent, underdeveloped or ectopic thyroid gland (dysgenesis), or by defected thyroid hormone biosynthesis (dyshormonogenesis). A genetic component has been identified in many cases of CH. This review summarizes the clinical and biochemical features of the genetic causes of primary CH.

METHODS

A literature review was conducted of gene defects causing congenital hypothyroidism.

RESULTS

Mutations in five genes have predominantly been implicated in thyroid dysgenesis (TSHR, FOXE1, NKX2-1, PAX8, and NKX2-5), the primary cause of CH (85%), and mutations in seven genes in thyroid dyshormonogenesis (SLC5A5, TPO, DUOX2, DUOXA2, SLC6A4, Tg, and DEHAL1). These genes encode for proteins that regulate genes expressed during the differentiation of the thyroid, such as TPO and Tg genes, or genes that regulate iodide organification, thyroglobulin synthesis, iodide transport, and iodotyrosine deiodination. Besides thyroid dysgenesis and dyshormonogenesis, additional causes of congenital hypothyroidism, such as iodothyronine transporter defects and resistance to thyroid hormones, have also been associated with genetic mutations.

CONCLUSION

The identification of the underlying genetic defects of CH is important for genetic counseling of families with an affected member, for identifying additional clinical characteristics or the risk for thyroid neoplasia and for diagnostic and management purposes.

Coexisting well-differentiated and anaplastic thyroid carcinoma in the same primary resection specimen: immunophenotypic and genetic comparison of the two components in a consecutive series of 13 cases and a review of the literature

Anaplastic carcinoma (AC) is a rare but highly aggressive form of thyroid cancer. It mostly arises on a background of pre-existing well-differentiated cancer (WDC); however, whether it evolves directly from a WDC or originates as a second independent neoplasm is still to be defined. To obtain further insights into these mechanisms, we performed morphological, immunohistochemical, and next-generation sequencing analyses to compare AC and its associated WDC in a subset of 13 surgically resected specimens. Histologically, most WDC were of aggressive subtypes. Papillary carcinomas (8 cases; 62%) were tall cell (4/8), columnar (1/8), classic with hobnail features (1/8), classic and follicular variant in the remaining 2 cases; Hürthle cell and follicular carcinomas were present in 5 (38%) and in 1 (8%) patient, respectively. One patient harbored both a PTC, follicular variant, and a Hürthle cell carcinoma. We did not find any correlation between a histotype of WDC and a specific anaplastic growth pattern. Immunohistochemically, ACs retained pankeratin/PAX8 expression but with significantly lower levels than WDCs, and they tended to lose TTF1 expression, as can be expected within a dedifferentiation process. In addition, AC showed a more frequent expression of p63 and/or SMA, a mutated pattern of p53, and an abnormal expression of p16. Genetic analysis showed that the number of mutations was higher in AC than in the associated WDC, confirming a role of the progressive accumulation of genetic damage in this transition. We observed that mutations found in the WDCs were consistently identified in the anaplastic counterparts, further supporting the hypothesis of a developmental link.

Anaplastic Thyroid Cancer Arising from Dyshormonogenetic Goiter: c.3070T>C and Novel c.7070T>C Mutation in the Thyroglobulin Gene

Concomitant thyroid cancer in patients with congenital thyroid dyshormonogenesis (TD) is extremely rare and few cases of differentiated thyroid cancer in patients with TD have been reported thus far. In this study, we describe anaplastic thyroid cancer in a 46-year-old woman with TD who had two germline thyroglobulin (TG) gene mutation, c.3790T>C (p, Cys1264Arg) in exon 17 and a novel c.7070T>C (p.Leu2357Pro) in exon 41 of the TG gene. Two affected younger sisters were also found to have the same TG mutation but not anaplastic thyroid cancer. Any thyroid nodular lesions that develop in patients with TD should be investigated carefully.

Novel Splicing of Immune System Thyroid Stimulating Hormone β-Subunit-Genetic Regulation and Biological Importance

Thyroid stimulating hormone (TSH), a glycoprotein hormone produced by the anterior pituitary, controls the production of thyroxine (T₄) and triiodothyronine (T₃) in the thyroid. TSH is also known to be produced by the cells of the immune system; however, the physiological importance of that to the organism is unclear. We identified an alternatively-spliced form of TSHβ that is present in both humans and mice. The TSHβ splice variant (TSHβv), although produced at low levels by the pituitary, is the primary form made by hematopoietic cells in the bone marrow, and by peripheral leukocytes. Recent studies have linked TSHβv functionally to a number of health-related conditions, including enhanced host responses to infection and protection against osteoporosis. However, TSHβv also has been associated with autoimmune thyroiditis in humans. Yet to be identified is the process by which the TSHβv isoform is produced. Here, a set of genetic steps is laid out through which human TSHβv is generated using splicing events that result in a novel transcript in which exon 2 is deleted, exon 3 is retained, and the 3' end of intron 2 codes for a signal peptide of the TSHβv polypeptide.

Pendred syndrome

Pendred syndrome is an autosomal recessive disorder that is classically defined by the combination of sensorineural deafness/hearing impairment, goiter, and an abnormal organification of iodide with or without hypothyroidism. The hallmark of the syndrome is the impaired hearing, which is associated with inner ear malformations such as an enlarged vestibular aqueduct (EVA). The thyroid phenotype is variable and may be modified by the nutritional iodine intake. Pendred syndrome is caused by biallelic mutations in the SLC26A4/PDS gene, which encodes the multifunctional anion exchanger pendrin. Pendrin has affinity for chloride, iodide, and bicarbonate, among other anions. In the inner ear, pendrin functions as a chloride/bicarbonate exchanger that is essential for maintaining the composition and the potential of the endolymph. In the thyroid, pendrin is expressed at the apical membrane of thyroid cells facing the follicular lumen. Functional studies have demonstrated that pendrin can mediate iodide efflux in heterologous cells. This, together with the thyroid phenotype observed in humans (goiter, impaired iodine organification) suggests that pendrin could be involved in iodide efflux into the lumen, one of the steps required for thyroid hormone synthesis. Iodide efflux can, however, also occur in the absence of pendrin suggesting that other exchangers or channels are involved. It has been suggested that Anoctamin 1 (ANO1/TMEM16A), a calcium-activated anion channel, which is also expressed at the apical membrane of thyrocytes, could participate in mediating apical efflux. In the kidney, pendrin is involved in bicarbonate secretion and chloride reabsorption. While there is no renal phenotype under basal conditions, severe metabolic alkalosis has been reported in Pendred syndrome patients exposed to an increased alkali load. This review provides an overview on the clinical spectrum of Pendred syndrome, the functional data on pendrin with a focus on its potential role in the thyroid, as well as the controversy surrounding the relative physiological roles of pendrin and anoctamin.

Use of thyroglobulin as a tumour marker

It is worthwhile to measure serum thyroglobulin (TG) level in thyroid cancer before subjecting patients to surgery for two reasons. Firstly, if the level is high, it may give a clue to the local and metastatic tumour burden at presentation; secondly, if the level is normal, it identifies the patients who are unlikely to show rising TG levels in the presence of thyroid cancer. Those who have high serum TG before surgery will show up recurrence as rising serum TG during the postoperative period. Those who do not have high serum TG before surgery will not show up rising serum TG in the presence of recurrent disease. In the latter situation, normal TG level gives only a false reassurance regarding recurrence of disease. Nevertheless, rising serum TG during the postoperative period must be interpreted cautiously because this could be due to the enlargement of non-cancerous residual thyroid tissue inadvertently left behind during surgery.

Targeted Foxe1 Overexpression in Mouse Thyroid Causes the Development of Multinodular Goiter But Does Not Promote Carcinogenesis

Recent genome-wide association studies have identified several single nucleotide polymorphisms in the forkhead box E1 gene (FOXE1) locus, which are strongly associated with the risk for thyroid cancer. In addition, our recent work has demonstrated FOXE1 overexpression in papillary thyroid carcinomas. To assess possible contribution of Foxe1 to thyroid carcinogenesis, transgenic mice overexpressing Foxe1 in their thyroids under thyroglobulin promoter (Tg-Foxe1) were generated. Additionally, Tg-Foxe1 mice were exposed to x-rays at the age of 5 weeks or crossed with Pten(+/-) mice to examine the combined effect of Foxe1 overexpression with radiation or activated phosphatidylinositol-3-kinase/Akt pathway, respectively. In 5- to 8-week-old Tg-Foxe1 mice, severe hypothyroidism was observed, and mouse thyroids exhibited hypoplasia of the parenchyma. Adult 48-week-old mice were almost recovered from hypothyroidism, their thyroids were enlarged, and featured colloid microcysts and multiple benign nodules of macrofollicular-papilloid growth pattern, but no malignancy was found. Exposure of transgenic mice to 1 or 8 Gy of x-rays and Pten haploinsufficiency promoted hyperplastic nodule formation also without carcinogenic effect. These results indicate that Foxe1 overexpression is not directly involved in the development of thyroid cancer and that proper Foxe1 dosage is essential for achieving normal structure and function of the thyroid.

Targeted Next-Generation Sequencing Analysis of a Pendred Syndrome-Associated Thyroid Carcinoma

Pendred syndrome is an autosomal recessive disorder characterized by hearing loss and goiter and is caused by bi-allelic mutations (homozygous or compound heterozygous) of the PDS (SLC26A4) gene. The incidence of Pendred syndrome is 7.5-10/100,000 in the general population, and it carries a 1 % risk of developing thyroid carcinoma. Herein, we report a case of a patient with Pendred syndrome who developed a follicular variant of papillary thyroid carcinoma (FVPTC)-that is approximately at an odd of 1/1,000,000. Targeted next-generation sequencing with ThyroSeq v2 was performed on the tumor, and only a TP53 mutation (TP53 p.R175H) was identified. The mutation was limited to the tumor nodule of FVPTC as shown by immunohistochemistry. This report represents the first extensive molecular study of a Pendred syndrome-associated thyroid carcinoma. The evidences support that thyroid carcinomas arising from dyshormonogenetic goiter require additional genetic alteration in addition to the purported thyroid-stimulating hormone (TSH) overstimulation. It is intrigue to note that the mutant p53 is involved in the development of a low-grade malignant thyroid tumor as FVPTC in this patient.

Reduction of Cellular Expression Levels Is a Common Feature of Functionally Affected Pendrin (SLC26A4) Protein Variants

Sequence alterations in the pendrin gene (SLC26A4) leading to functionally affected protein variants are frequently involved in the pathogenesis of syndromic and nonsyndromic deafness. Considering the high number of SLC26A4 sequence alterations reported to date, discriminating between functionally affected and unaffected pendrin protein variants is essential in contributing to determine the genetic cause of deafness in a given patient. In addition, identifying molecular features common to the functionally affected protein variants can be extremely useful to design future molecule-directed therapeutic approaches. Here we show the functional and molecular characterization of six previously uncharacterized pendrin protein variants found in a cohort of 58 Brazilian deaf patients. Two variants (p.T193I and p.L445W) were undetectable in the plasma membrane, completely retained in the endoplasmic reticulum and showed no transport function; four (p.P142L, p.G149R, p.C282Y and p.Q413R) showed reduced function and significant, although heterogeneous, expression levels in the plasma membrane. Importantly, total expression levels of all of the functionally affected protein variants were significantly reduced with respect to the wild-type and a fully functional variant (p.R776C), regardless of their subcellular localization. Interestingly, reduction of expression may also reduce the transport activity of variants with an intrinsic gain of function (p.Q413R). As reduction of overall cellular abundance was identified as a common molecular feature of pendrin variants with affected function, the identification of strategies to prevent reduction in expression levels may represent a crucial step of potential future therapeutic interventions aimed at restoring the transport activity of dysfunctional pendrin variants.

Biological Impact of the TSHβ Splice Variant in Health and Disease

Thyroid stimulating hormone (TSH), a glycoprotein hormone composed of α and β chains, is produced by thyrotrope cells of the anterior pituitary. Within the conventional endocrine loop, pituitary-derived TSH binds to receptors in the thyroid, resulting in the release of the thyroid hormones thyroxine (T₄) and triiodothyronine (T₃). T₄ and T₃ in turn regulate nearly every aspect of mammalian physiology, including basal metabolism, growth and development, and mood and cognition. Although TSHβ has been known for years to be produced by cells of the immune system, the significance of that has remained largely unclear. Recently, a splice variant of TSHβ (TSHβv), which consists of a truncated but biologically functional portion of the native form of TSHβ, was shown to be produced by bone marrow cells and peripheral blood leukocytes, particularly cells of the myeloid/monocyte lineage. In contrast, full-length native TSHβ is minimally produced by cells of the immune system. The present article will describe the discovery of the TSHβv and will discuss its potential role in immunity and autoimmunity, inflammation, and bone remodeling.

Papillary thyroid carcinoma in one of identical twin patients with Pendred syndrome

Pendred syndrome is an autosomal recessive disorder characterized by sensorineural deafness, a partial defect in iodide organification, and dyshormonogenetic goiter. Several cases of Pendred syndrome with follicular thyroid carcinomas were reported previously. Here we report identical twin patients with Pendred syndrome, who had thyroid tumors with distinct histopathological findings. 34-year-old identical twins with congenital deafness and goiter were referred to our hospital with complaint of neck discomfort. The genetic testing showed that these twin patients were compound heterozygotes carrying the same two mutations in the Pendred's syndrome (PDS / SLC26A4) gene (c2168A > G and ins2110GCTGG), which confirmed the diagnoses of Pendred syndrome. They underwent thyroidectomy. Histological examination of the thyroid tumors resected from these twin patients revealed follicular variant of papillary thyroid carcinoma, and diffuse and nodular goiter without any evidence of malignancy, respectively. To our knowledge, the former is the first case of follicular variant of papillary thyroid carcinoma in Pendred Syndrome.

Minimally invasive follicular thyroid carcinoma developed in dyshormonogenetic multinodular goiter due to thyroid peroxidase gene mutation

BACKGROUND

The occurrence of thyroid carcinoma in patients with congenital hypothyroidism (CH) caused by dyshormonogenesis is very rare, and has only been reported in one patient harboring mutations in the thyroid peroxidase (TPO) gene.

PATIENT FINDINGS

We report on a 29-year follow-up of two consanguineous siblings with CH due to total iodide organification defect who also had sensorineural hearing loss. Molecular analysis revealed a novel biallelic mutation of the TPO gene in which phenylalanine substitutes serine at codon 292 (c.875C>T, p.S292F) in exon 8. Despite early initiation, adequate doses of levothyroxine treatment and consequently normal thyrotropin (TSH) levels, the proposita developed a huge multinodular goiter (MNG) and underwent total thyroidectomy due to tracheal compression. Pathological examination revealed a unifocal follicular thyroid carcinoma without vascular invasion in the left lobe of the thyroid gland.

SUMMARY

Our finding of follicular thyroid carcinoma arising from dyshormonogenetic MNG in a patient without elevated serum TSH levels indicates that genetic and environmental factors other than TSH level might be involved in the development of thyroid carcinoma in dyshormonogenetic MNG.

CONCLUSIONS

Despite the rare occurrence of thyroid carcinoma in dyshormonogenetic MNG, we recommend long-term follow-up and regular neck ultrasound imaging to prevent delayed diagnosis of thyroid carcinoma.

Monocarboxylate transporter 8 deficiency: altered thyroid morphology and persistent high triiodothyronine/thyroxine ratio after thyroidectomy

CONTEXT

Thyroid hormone transport across the plasma membrane depends on transmembrane transport proteins, including monocarboxylate transporter 8 (MCT8). Mutations in MCT8 (or SLC16A2) lead to a severe form of X-linked psychomotor retardation, which is characterised by elevated plasma triiodothyronine (T(3)) and low/normal thyroxine (T(4)). MCT8 contributes to hormone release from the thyroid gland.

OBJECTIVE

To characterise the potential impact of MCT8-deficiency on thyroid morphology in a patient and in Mct8-deficient mice.

DESIGN

Thyroid morphology in a patient carrying the A224V mutation was followed by ultrasound imaging for over 10 years. After thyroidectomy, a histopathological analysis was carried out. The findings were compared with histological analyses of mouse thyroids from the Mct8(-/y) model.

RESULTS

We show that an inactivating mutation in MCT8 leads to a unique, progressive thyroid follicular pathology in a patient. After thyroidectomy, histological analysis revealed gross morphological changes, including several hyperplastic nodules, microfollicular areas with stromal fibrosis and a small focus of microfollicular structures with nuclear features reminiscent of papillary thyroid carcinoma (PTC). These findings are supported by an Mct8-null mouse model in which we found massive papillary hyperplasia in 6- to 12-month-old mice and nuclear features consistent with PTC in almost 2-year-old animals. After complete thyroidectomy and substitution with levothyroxine (l-T(4)), the preoperative, inadequately low T(4) and free T(4) remained, while increasing the l-T(4) dosage led to T(3) serum concentrations above the normal range.

CONCLUSIONS

Our results implicate peripheral deiodination in the peculiar hormonal constellation of MCT8-deficient patients. Other MCT8-deficient patients should be closely monitored for potential thyroid abnormalities.

Thyroid cancer of follicular cell origin in inherited tumor syndromes

Well-differentiated thyroid cancer accounts for 95% of thyroid malignancies. In contrast to medullary thyroid carcinoma, in which about 25% are familial, only 5% of follicular cell-derived thyroid carcinomas are a component of a familial cancer syndrome. The familial follicular cell-derived tumors or nonmedullary thyroid carcinoma encompass a heterogeneous group of diseases, and are classified into 2 distinct groups: syndromic-associated tumors, occurring in syndromes in which nonmedullary thyroid carcinomas are the predominant tumor encountered, and nonsyndromic tumors, those occurring in tumor syndromes in which thyroid involvement is a minor component. The first group, syndromic-associated tumors, includes phosphase and tensin (PTEN)-hamartoma tumor syndrome/Cowden syndrome, familial adenomatous polyposis/Gardner syndrome, Carney complex type 1, Werner syndrome, and Pendred syndrome. Other syndromes, as McCune Albright syndrome, Peutz-Jeghers syndrome, and Ataxia-teleangiectasia syndrome may be associated with the development of follicular cell-derived tumors, but the link is less established than the above syndromes. The syndromic-associated tumors are the focus of this review. The second group of familial follicular cell-derived tumors syndromes or nonsyndromic tumors, in which nonmedullary thyroid carcinomas are the major findings, include pure familial papillary thyroid carcinoma, with or without oxyphilia, familial papillary thyroid carcinoma with papillary renal cell carcinoma, and familial papillary thyroid carcinoma with multinodular goiter. This review will discuss the clinical and pathological findings of the patients with familial syndrome-associated tumors: PTEN-hamartoma tumor syndrome/Cowden syndrome, familial adenomatous polyposis syndrome, Carney complex type 1, Werner syndrome, and Pendred syndrome.

Immunological regulation of metabolism--a novel quintessential role for the immune system in health and disease

The hypothalamus-pituitary-thyroid (HPT) axis is an integrated hormone network that is essential for maintaining metabolic homeostasis. It has long been known that thyroid stimulating hormone (TSH), a central component of the HPT axis, can be made by cells of the immune system; however, the role of immune system TSH remains enigmatic and most studies have viewed it as a cytokine used to regulate immune function. Recent studies now indicate that immune system-derived TSH, in particular, a splice variant of TSHβ that is preferentially made by cells of the immune system, is produced by a subset of hematopoietic cells that traffic to the thyroid. On the basis of these and other findings, we propose the novel hypothesis that the immune system is an active participant in the regulation of basal metabolism. We further speculate that this process plays a critical role during acute and chronic infections and that it contributes to a wide range of chronic inflammatory conditions with links to thyroid dysregulation. This hypothesis, which is amenable to empirical analysis, defines a previously unknown role for the immune system in health and disease, and it provides a dynamic connection between immune-endocrine interactions at the organismic level.

Familial syndromes associated with thyroid cancer in the era of personalized medicine

BACKGROUND

Well-differentiated thyroid cancer accounts for 95% of thyroid malignancies, and 5% of these patients will have familial disease. This compares to 25% of patients with medullary thyroid cancer (MTC) having a familial form; however, this accounts for only 1% of all patients with thyroid cancer. Most cases of familial thyroid cancer are nonmedullary (NMFTC), and have been shown to be present in familial cancer syndromes such as familial adenomatous polyposis, Cowden syndrome, Carney complex, Pendred syndrome, and Werner syndrome. This review discusses the contemporary management of the patients with familial-syndrome-associated thyroid cancer based on their individual risks for developing thyroid cancer.

SUMMARY

Most of the progress in the genetics of familial thyroid cancer has been in patients with MTC. The mutations in patients with isolated NMFTC have not been as well defined as in MTC. They are likely autosomal dominant with reduced penetrance. The patients with these familial syndromes most likely have a susceptibility gene that increases the risk of thyroid cancer. Most of the patients with a familial syndrome and NMFTC will have papillary thyroid carcinoma, suggesting that a specific gene for papillary thyroid carcinoma may also be present. In many cases, patients have a known familial syndrome that has defined risk for thyroid cancer.

CONCLUSIONS

Patients with familial syndromes that are associated with thyroid cancer can be individually categorized based on syndrome risks for developing thyroid cancer. The clinician must also be knowledgeable in recognizing the possibility of an underlying familial syndrome when a patient presents with thyroid cancer.

Biallelic p.R2223H mutation in the thyroglobulin gene causes thyroglobulin retention and severe hypothyroidism with subsequent development of thyroid carcinoma

CONTEXT

Dyshormonogenesis due to genetic defect in thyroglobulin (Tg) synthesis and secretion can lead to congenital hypothyroidism.

OBJECTIVES

The aim of the study was to analyze the TG gene for the presence of mutations and to study the underlying mechanisms leading to dyshormonogenesis.

CASES

Two siblings aged 25 and 31 yr presented with recurrent goitrous hypothyroidism with undetectable serum Tg. The older sibling was diagnosed with follicular variant of papillary thyroid carcinoma (FVPTC) at age 21 and metastatic FVPTC 8 yr later.

METHODS

The entire coding region of TG gene was sequenced. BRAF, RAS, and P53 mutations or PAX8/PPAR-gamma rearrangement were screened in the FVPTC. Tg expression was studied by immunohistochemistry.

RESULTS

Biallelic c.6725G>A (p.R2223H) and c.6396C>T (p.S2113L) sequence variations were detected in both patients and monoallelic variations in their family members. The c.6396C>T (p.S2113L) sequence variation was found in 14% of 100 population controls, whereas c.6725G>A variation was not present in the controls. Two previously reported polymorphisms (c.2200T>G and c.3082A>G) were present in all the family members. Strong cytoplasmic immunostaining of Tg was observed in the hyperplastic thyroid epithelial cells and weak or no staining in the follicular lumen. Cytoplasmic staining was localized in the endoplasmic reticulum. Reduced staining was found in the FVPTC. Neither RAS, BRAF, or P53 gene mutation nor a PAX8/PPAR-gamma rearrangement was detected in the tumor tissue.

CONCLUSIONS

Biallelic c.6725G>A (p.R2223H) mutation causes Tg retention in the endoplasmic reticulum, resulting in dyshormonogenesis. Prolonged TSH stimulation may promote malignant transformation and development of thyroid cancer. The c.6396C>T (p.S2113L) is a novel polymorphism.

Mutations of the thyroglobulin gene and its relevance to thyroid disorders

PURPOSE OF REVIEW

To perform an update review on thyroglobulin gene mutations associated with congenital hypothyroidism, thyroid cancer, and autoimmunity.

RECENT FINDINGS

Forty-two thyroglobulin mutations have been identified in dyshormonogenetic congenital hypothyroidism. Clinical and laboratory criteria defining defective thyroglobulin synthesis are mostly related to thyroglobulin mutations, generally caused by intracellular thyroglobulin transport defects to the colloid rather than defects in thyroid hormones synthesis. Some mutated thyroglobulin may escape the rigorous chaperone control and reach the colloid, allowing a wide phenotypic spectrum that includes euthyroidism in an adequate iodine environment. In some patients, continuous levothyroxine treatment does not reduce elevated serum thyroid-stimulating hormone (TSH) levels that may lead to goiter development. Prenatally, inactive mutant thyroglobulin will not be able to synthesize thyroid hormones and may increase pituitary thyrotroph threshold for thyroid hormone feedback. Congenital goiter is a risk factor for thyroid cancer and some thyroglobulin variants may confer susceptibility to thyroid autoimmunity.

SUMMARY

Advances in the understanding of thyroglobulin genetic defects and its severity should allow researchers to perform adequate molecular diagnosis, genetic counseling, and intrauterine treatment to prevent subtle deficits in central nervous system development. This knowledge should improve the understanding of physiological functions of the thyroid and influence of nutritional iodine.

Evaluation of the thyroid in patients with hearing loss and enlarged vestibular aqueducts

OBJECTIVE

To evaluate thyroid structure and function in patients with enlargement of the vestibular aqueduct (EVA) and sensorineural hearing loss.

DESIGN

Prospective cohort survey.

SETTING

National Institutes of Health Clinical Center, a federal biomedical research facility.

PATIENTS

The study population comprised 80 individuals, aged 1.5 to 59 years, ascertained on the basis of EVA and sensorineural hearing loss.

MAIN OUTCOME MEASURES

Associations among the number of mutant alleles of SLC26A4; volume and texture of the thyroid; percentage of iodine 123 ((123)I) discharged at 120 minutes after administration of perchlorate in the perchlorate discharge test; and peripheral venous blood levels of thyrotropin, thyroxine, free thyroxine, triiodothyronine, thyroglobulin, antithyroid peroxidase and antithyroglobulin antibodies, and thyroid-binding globulin.

RESULTS

Thyroid volume is primarily genotype dependent in pediatric patients but age dependent in older patients. Individuals with 2 mutant SLC26A4 alleles discharged a significantly (P < or = .001) greater percentage of (123)I compared with those with no mutant alleles or 1 mutant allele. Thyroid function, as measured by serologic testing, is not associated with the number of mutant alleles.

CONCLUSIONS

Ultrasonography with measurement of gland volume is recommended for initial assessment and follow-up surveillance of the thyroid in patients with EVA. Perchlorate discharge testing is recommended for the diagnostic evaluation of patients with EVA along with goiter, nondiagnostic SLC26A4 genotypes (zero or 1 mutant allele), or both.

A molecular analysis and long-term follow-up of two siblings with severe congenital hypothyroidism carrying the IVS30+1G>T intronic thyroglobulin mutation

OBJECTIVE: To extend the molecular analysis of the IVS30+1G>T intronic thyroglobulin (TG) mutation, and to report the eleven year follow-up of the affected patients. METHOSD: Two siblings with severe congenital hypothyroidism with fetal and neonatal goiter, harboring the IVS30+1G>T mutation were included. Nodular and non-nodular thyroid tissue specimens were collected. Specific thyroid genes expression was evaluated by real-timePCR and by immunohistochemistry. RESULTS: In non-nodular tissue specific thyroid genes mRNA were reduced when compared to normal thyroid sample. In the nodule, TPO and NIS expression was very low. Microscopic examinations showed very large follicular-lumina and swollen vesicles of endoplasmatic-reticulum. Strong cytoplasmatic and low follicular-lumen TG immunostaining were detected. Intracellular NIS, membrane TPO and TSHR immunostaining had higher positivity in non-nodular sample. Both patients had a long-term adequate developmental outcome, besides one patient have been lately-treated. CONCLUSIONS: IVS30+1G>T mutation not only lead to very enlarge endoplasmatic-reticulum, but also to alterations of specific thyroid genes expression. The clinical evolution of patients harboring these mutations strengthen the concept of the influence of environment, like iodine nutrition, to determine the final phenotypic appearance.

Two common and three novel PDS mutations in Thai patients with Pendred syndrome

Pendred syndrome is an autosomal recessive disorder characterized by congenital sensorineural deafness, goiter, and impaired iodide organification. It is caused by mutations in the PDS gene. Most published mutation studies of Pendred syndrome have dealt with Western populations. In this study, we examined clinical and molecular characteristics of 16 affected individuals in 6 unrelated Thai families. Of all the affected, 100% (16/16) had bilateral deafness, 68.8% (11/16) goiters, and 25% (4/16) hypothyroidism. Follicular thyroid carcinoma and Hürthle cell adenoma were found in affected members of a family, raising the possibility of an increased risk of thyroid carcinoma in Pendred syndrome patients. Sequence analysis of the entire coding region of the PDS gene successfully identified all 12 mutant alleles in these 6 families. The 12 identified mutant alleles constituted 6 distinct mutations including 3 splice site mutations (IVS4-1G>A, IVS7-2A>G, IVS9- 1G>A), one frame shift mutation (1548insC) and 2 missense mutations (T67S, H723R). Eight mutations out of 12 were constituted by IVS7- 2A>G and 1548insC, each one being present in 4 distinct alleles in our studied group. The identification of these two frequent PDS mutations will facilitate the molecular diagnosis of Pendred syndrome in Thai populations. In addition, three newly identified mutations, T67S, IVS4-1G>A, and IVS9-1G>A, were not observed in 50 unrelated healthy Thai controls.

Clinical case seminar: metastatic follicular thyroid carcinoma arising from congenital goiter as a result of a novel splice donor site mutation in the thyroglobulin gene

CONTEXT

Defects in thyroglobulin (Tg) synthesis are one of the causes of thyroid dyshormonogenesis. Only a few mutations in the Tg gene have been described.

OBJECTIVES

We describe a novel Tg gene mutation and discuss the mechanisms by which it causes dyshormonogenesis with subsequent malignant transformation.

CASES

Two siblings aged 21 and 19 yr presented with recurrent goiters for which they had undergone multiple thyroid surgeries since early childhood. The older sibling was diagnosed with metastatic follicular thyroid carcinoma at age 15 yr.

METHODS

The entire coding region and intron-exon boundaries of the Tg gene were amplified and sequenced from the patients. We also sequenced the boundaries of exon 5 and intron 5 from both parents. RT-PCR amplification of a cDNA fragment encompassing exons 4-6 was also performed.

RESULTS

A homozygous G to A point mutation at position +1 of the splice donor site of intron 5 (g.IVS5+1G-->A) was detected in both patients, whereas a monoallelic mutation was found in their parents. RT-PCR amplification of a cDNA fragment covering exons 4-6 revealed a 191-bp fragment in the patients and 351- and 191-bp fragments in the parents. Sequence analysis of these two fragments confirmed deletion of exon 5 in the 191-bp fragment.

CONCLUSIONS

Aberrant splicing occurred as a result of the g.IVS5+1G-->A mutation, which caused fusion of exons 4 and 6, resulting in the frame shift at codon position 141 and a premature stop codon at position 147 (FS141-->147X). The malignant transformation is likely a result of prolonged TSH stimulation.

High incidence of thyroid cancer in long-standing goiters with thyroglobulin mutations

In this paper, we report the high prevalence of thyroid malignancy in patients with thyroglobulin mutations in Japan. Mutations of the thyroglobulin gene cause defective thyroid hormone synthesis, resulting in congenital hypothyroidism. Since our report in 1999 on the thyroglobulin mutations C1264R and C1996S, we have identified 14 adult patients (7 males and 7 females) from 9 unrelated families. They visited hospitals for treatment of huge goiters that first appeared in childhood. Persistent growth of the thyroid gland, probably caused by thyrotropin (TSH) stimulation, partially compensated thyroid hormone production, resulting in lowered serum TSH concentrations in turn. Consequently, many patients had to undergo multiple operations. Of 11 patients who had undergone surgery, 7 had thyroid cancers. Of five patients whose thyroid tissue was available, we found a heterozygous activating mutation, either V599E or K600E, in cancerous tissue from each of 2 patients. From these observations, we conclude that goiter resulting from thyroglobulin mutations is associated with thyroid cancer.

Molecular analysis of the PDS gene in a nonconsanguineous Sicilian family with Pendred's syndrome

OBJECTIVE

The autosomal recessive Pendred's syndrome is defined by congenital sensorineural deafness, goiter, and impaired iodide organification. It is caused by mutations in the Pendred's syndrome (PDS) gene that encodes pendrin, a chloride/iodide transporter expressed in the thyroid, the inner ear, and the kidney. In this study we performed clinical and molecular analyses in three siblings from a nonconsanguineous Sicilian family who presented with the clinical features of Pendred's syndrome. PATIENTS AND MOLECULAR ANALYSES: In two sisters and one brother, the clinical diagnosis of Pendred's syndrome was established based on the findings of sensorineural hearing loss and large goiters. Thyroid function tests, perchlorate discharge tests, thyroid ultrasound, and scintigraphy were performed in all affected individuals. Exons 2 to 21 of the PDS gene were amplified by polymerase chain reaction (PCR) and both strands were submitted to direct sequence analysis.

RESULTS

The clinical diagnosis of Pendred's syndrome was supported by a positive perchlorate discharge test in the three afflicted siblings. Direct sequence analysis of the PDS gene revealed that all three harbored one allele with a novel mutation 890delC leading to a frameshift mutation and premature stop codon at position 302 (FS297 > 302X). On the other allele, two of the siblings had a previously described transition 1226G > A, which results in the substitution of arginine by histidine at position 409 (R409H). In the index patient, no mutation could be identified on the other allele. In functional studies, these mutants lose the ability of pendrin to mediate iodide efflux.

CONCLUSIONS

All three patients included in this study presented with the classic Pendred syndrome triad. Two siblings were compound heterozygous for mutations in the coding region of the PDS gene. The third individual could have an unidentified mutation in a regulatory or intronic region of the PDS gene, or an identical phenotype caused by distinct pathogenic mechanisms.

An outline of inherited disorders of the thyroid hormone generating system

To date, various genetic defects impairing the biosynthesis of thyroid hormone have been identified. These congenital heterogeneous disorders result from mutations of genes involved in many steps of thyroid hormone synthesis, storage, secretion, delivery, or utilization. In contrast to thyroid dyshormonogenesis, the elucidation of the underlying etiology of most cases of thyroid dysgenesis is much less understood. It is suggested that genetic factors might play a role in some cases of thyroid dysgenesis and the best candidate genes involved are those encoding transcription factors known to play a role in the embryonic development of the thyroid gland. Moreover, discordance for thyroid dysgenesis is the rule for monozygotic twins as recently reported and this may result from epigenetic phenomena, early somatic mutations, or postzygotic events. In the final part of this review the molecular defects involved in proteins that transport thyroid hormone in the circulation are described: thyroxine-binding globulin (TBG), transtiretin and albumin, that may be associated with altered thyroid function tests and other pathologic conditions such as amyloidotic polyneuropathy.