Mass spectrometry in the diagnosis of thyroid disease and in the study of thyroid hormone metabolism.

The importance of thyroid hormones in the regulation of development, growth, and energy metabolism is well known. Over the last decades, mass spectrometry has been extensively used to investigate thyroid hormone metabolism and to discover and characterize new molecules involved in thyroid hormones production, such as thyrotropin-releasing hormone. In the earlier period, the quantification methods, usually based on gas chromatography-mass spectrometry, were complicated and time consuming. They were mainly focused on basic research, and were not suitable for clinical diagnostics on a routine basis. The development of the modern mass spectrometers, mainly coupled to liquid chromatography, enabled simpler sample preparation procedures, and the accurate quantification of thyroid hormones, of their precursors, and of their metabolites in biological fluids, tissues, and cells became feasible. Nowadays, molecules of physiological and pathological interest can be assayed also for diagnostic purposes on a routine basis, and mass spectrometry is slowly entering the clinical laboratory. This review takes stock of the advancements in the field of thyroid metabolism that were carried out with mass spectrometry, with special focus on the use of this technique for the quantification of molecules involved in thyroid diseases.

Identification of Two Different Phenotypes of Patients with Amiodarone-Induced Thyrotoxicosis and Positive Thyrotropin Receptor Antibody Tests.

Introduction: Serum thyrotropin (TSH) receptor antibodies (TRAbs) are occasionally found in patients with amiodarone-induced thyrotoxicosis (AIT), and usually point to a diagnosis of type 1 AIT (AIT1) due to Graves' disease (GD). However, the TRAb role and function in AIT have not been clarified. Methods: A retrospective cohort study of 309 AIT patients followed at a single academic center over a 30-year period. AIT TRAb-positive patients (n = 21, 7% of all cases) constituted the study group; control groups consisted of type 2 AIT (AIT2) TRAb-negative patients (n = 233), and 100 non-AIT patients with GD. Clinical and biochemical data at diagnosis and during the course of disease were compared. Histological samples of patients who had total thyroidectomy were reviewed. Stored serum samples were used for a functional assay of TRAb class G immunoglobulins (IgGs) in Chinese hamster ovary (CHO) cells stably transfected with complementary DNA encoding for the TSH receptor. Results: TRAb-positive patients were grouped according to color flow Doppler sonography, radioactive iodine thyroid uptake, and duration of amiodarone therapy before thyrotoxicosis in type 1 (n = 9, 43%; TRAb1) or type 2 (n = 12, 57%; TRAb2) AIT. TRAb1 patients had clinical and biochemical features indistinguishable from GD controls, and were responsive to methimazole. Conversely, TRAb2 patients had clinical features similar to AIT2 controls, and were responsive to glucocorticoids, but not to methimazole. The CHO cell functional assay demonstrated that TRAb1 IgGs had a stimulatory effect on cyclic AMP production, which was absent in TRAb2 IgGs. Pathology in TRAb1 showed hyperplastic thyroid follicles and mild lymphocyte infiltration, reflecting thyroid stimulation. On the contrary, TRAb2 samples revealed follicle destruction, macrophage infiltration, and sometimes fibrosis, consistent with a destructive process. Conclusions: Almost 60% of TRAb-positive AIT patients had a destructive thyroiditis. TRAb-positive tests in AIT patients do thus not necessarily imply a diagnosis of GD and AIT1, and should be evaluated in the clinical and biochemical setting of each AIT patient and confirmed by measuring thyroid-stimulating immunoglobulins.

Characterization of a novel mutation V136L in bone morphogenetic protein 15 identified in a woman affected by POI.

BACKGROUND: Premature ovarian insufficiency (POI) is an ovarian defect characterized by primary or secondary amenorrhea, hypergonadotropism and hypoestrogenism which occurs before the age of 40 years with a major genetic component. In this study we performed clinical evaluation and genetic analysis of a group of 18 patients with POI. The study involved 18 consecutive women with POI. Karyotiping and genetic analysis for research of mutations in GDF9 (Growth Differentation Factor 9) and BMP15 (Bone morphogentic protein 15) genes and FMR1 (Fragile X Mental Retardation 1) premutation were carried out. In vitro functional study of the novel BMP15 mutation was performed using COV434 (Human ovarian granulosa tumour cells 434) cells of ovarian granulosa, which consistently express BMP responsive element, and luciferase reporter assay. RESULTS: Three patients (17%) had a family history of POI. Ten patients (56%) had a family history of autoimmune diseases and nine patients (50%) showed a personal history of one or more autoimmune diseases. Of patients for whom morphological assessment was available, almost half (44%) had poor follicle assets or small ovaries's size at pelvic US. Two patients (13%) showed reduced bone density at DEXA (Dual Energy X-ray Absorptiometry). All the women had normal female kariotype and no mutations in the GDF-9 gene or FMR1 premutations were found. A novel heterozygous mutation c.406G > C (V136L) of BMP15 gene was identified in one patient. After transfection in COV434 cells, BMP15 variant showed a significantly reduced luciferase activity compared to wild type. CONCLUSIONS: POI is a multifactorial disease with several health implications. Autoimmunity and genetics represent the most common aetiology. We identified and characterized a novel BMP15 mutation, providing an additional elucidation of molecular basis of this complex disorder.

Clinical features, risk of mass enlargement, and development of endocrine hyperfunction in patients with adrenal incidentalomas: a long-term follow-up study.

PURPOSE: To evaluate the risk of mass enlargement and endocrine function modification in patients with adrenal incidentaloma (AI). METHODS: In this retrospective study, we examined clinical and hormonal characteristics of 310 patients with AI (200 females and 110 males; age: 58.3 ± 12.9 years), followed up for a median (interquartile range) of 31.4 months (13.0-78.6) and evaluated for possible modification in adrenal mass size and hormonal function. The hormonal evaluation included morning serum cortisol and plasma ACTH at 8 a.m., aldosterone, plasma renin activity/direct renin concentration, and 24-h urine metanephrines/normetanephrines. One microgram overnight dexamethasone suppression test (DST) was performed. Autonomous cortisol secretion (ACS) was diagnosed in the presence of cortisol after 1 mg DST > 5 µg/dl (138 nmol/l) or >1.8 and ≤5 µg/dl (50-138 nmol/l) and at least one of the following: (i) low ACTH; (ii) increased 24-h urinary-free cortisol; (iii) absence of cortisol rhythm; and (iv) post-LDDST cortisol level > 1.8 µg/dl (50 nmol/l). When there was no biochemical evidence of adrenal hormonal hyperactivity, AIs were classified as nonfunctioning (NFAIs). The mass was considered significantly enlarged when the size increase was more than 20% and at least 5 mm compared to baseline. RESULTS: At diagnosis, NFAIs were found in 209 patients, while ACS and overt adrenal hyperfunction were diagnosed in 81 and 20 patients, respectively. During follow-up, 3.3% and 1.5% of patients with NFAI developed subtle and overt endocrine hyperfunction, respectively, while a significant mass enlargement was observed in 17.7% of all AIs. The risk of developing ACS was significantly higher in patients with adenoma >28 mm (hazard ratio [HR] 12.4; 95% confidence interval [CI], 2.33-66.52, P = 0.003), in those with bilateral adrenal tumors (HR: 5.36; 95% CI, 1.17-24.48, P = 0.030), and with low/suppressed ACTH values (HR: 11.2, 95% CI 2.06-60.77; P = 0.005). The risk of mass enlargement was lower for patients in the fourth quartile of body mass index than those in the first quartile (HR 0.33; 95% CI, 0.14-0.78; P = 0.012). CONCLUSIONS: In patients with AI, the risk of developing hormonal hyperfunction and mass enlargement is overall low, although some tumor characteristics and anthropometric features might increase this risk. Taking account of all these aspects is important for planning a tailored follow-up in AI patients.

TSH elevations as the first laboratory evidence for pseudohypoparathyroidism type Ib (PHP-Ib).

Hypocalcemia and hyperphosphatemia because of resistance toward parathyroid hormone (PTH) in the proximal renal tubules are the most prominent abnormalities in patients affected by pseudohypoparathyroidism type Ib (PHP-Ib). In this rare disorder, which is caused by GNAS methylation changes, resistance can occur toward other hormones, such as thyroid-stimulating hormone (TSH), that mediate their actions through G protein-coupled receptors. However, these additional laboratory abnormalities are usually not recognized until PTH-resistant hypocalcemia becomes clinically apparent. We now describe four pediatric patients, first diagnosed with subclinical or overt hypothyroidism between the ages of 0.2 and 15 years, who developed overt PTH-resistance 3 to 20 years later. Although anti-thyroperoxidase (anti-TPO) antibodies provided a plausible explanation for hypothyroidism in one of these patients, this and two other patients revealed broad epigenetic GNAS abnormalities, which included loss of methylation (LOM) at exons AS, XL, and A/B, and gain of methylation at exon NESP55; ie, findings consistent with PHP-Ib. LOM at GNAS exon A/B alone led in the fourth patient to the identification of a maternally inherited 3-kb STX16 deletion, a well-established cause of autosomal dominant PHP-Ib. Although GNAS methylation changes were not detected in additional pediatric and adult patients with subclinical hypothyroidism (23 pediatric and 39 adult cases), hypothyroidism can obviously be the initial finding in PHP-Ib patients. One should therefore consider measuring PTH, along with calcium and phosphate, in patients with unexplained hypothyroidism for extended periods of time to avoid hypocalcemia and associated clinical complications.

The different requirement of L-T4 therapy in congenital athyreosis compared with adult-acquired hypothyroidism suggests a persisting thyroid hormone resistance at the hypothalamic-pituitary level.

BACKGROUND: Levothyroxine (l-T4) is commonly employed to correct hormone deficiency in children with congenital hypothyroidism (CH) and in adult patients with iatrogenic hypothyroidism. OBJECTIVE: To compare the daily weight-based dosage of the replacement therapy with l-T4 in athyreotic adult patients affected by CH and adult patients with thyroid nodular or cancer diseases treated by total thyroidectomy. DESIGN AND METHODS: A total of 36 adult patients (27 females and nine males) aged 18-29 years were studied; 13 patients (age: 21.5±2.1, group CH) had athyreotic CH treated with l-T4 since the first days of life. The remaining 23 patients (age: 24±2.7, group AH) had hypothyroidism after total thyroidectomy (14 patients previously affected by nodular disease and nine by thyroid carcinoma with clinical and biochemical remission). Patient weight, serum free thyroid hormones, TSH, thyroglobulin (Tg), anti-Tg, and anti-thyroperoxidase antibodies were measured. Required l-T4 dosage was evaluated. At the time of the observations, all patients presented free thyroid hormones within the normal range and TSH between 0.8 and 2 µIU/ml. RESULTS: Patients had undetectable Tg and anti-thyroid antibodies. The daily weight-based dosage of the replacement therapy with l-T4 to reach euthyroidism in patients of group CH was significantly higher than that in those of group AH (2.16±0.36 vs 1.73±0.24 µg/kg, P<0.005). Patients of group CH treated with l-T4 had significantly higher serum TSH levels than patients of group AH (P=0.05) as well as higher FT4 concentrations. CONCLUSIONS: To correct hypothyroidism, patients of group CH required a daily l-T4 dose/kg higher than group AH patients, despite higher levels of TSH. The different requirement of replacement therapy between adult patients with congenital and those with surgical athyroidism could be explained by a lack of thyroid hormones since fetal life in CH, which could determine a different set point of the hypothalamus-pituitary-thyroid axis.

Identification of a novel pax8 gene sequence variant in four members of the same family: from congenital hypothyroidism with thyroid hypoplasia to mild subclinical hypothyroidism.

BACKGROUND: Congenital hypothyroidism is often secondary to thyroid dysgenesis, including thyroid agenesis, hypoplasia, ectopic thyroid tissue or cysts. Loss of function mutations in TSHR, PAX8, NKX2.1, NKX2.5 and FOXE1 genes are responsible for some forms of inherited congenital hypothyroidism, with or without hypoplastic thyroid. The aim of this study was to analyse the PAX8 gene sequence in several members of the same family in order to understand whether the variable phenotypic expression, ranging from congenital hypothyroidism with thyroid hypoplasia to mild subclinical hypothyroidism, could be associated to the genetic variant in the PAX8 gene, detected in the proband. METHODS: We screened a hypothyroid child with thyroid hypoplasia for mutations in PAX8, TSHR, NKX2.1, NKX2.5 and FOXE1 genes. We studied the inheritance of the new variant R133W detected in the PAX8 gene in the proband's family, and we looked for the same substitution in 115 Caucasian European subjects and in 26 hypothyroid children. Functional studies were performed to assess the in vitro effect of the newly identified PAX8 gene variant. RESULTS: A new heterozygous nucleotide substitution was detected in the PAX8 DNA-binding motif (c.397C/T, R133W) in the proband, affected by congenital hypothyroidism with thyroid hypoplasia, in his older sister, displaying a subclinical hypothyroidism associated with thyroid hypoplasia and thyroid nodules, in his father, affected by hypothyroidism with thyroid hypoplasia and thyroid nodules, and his first cousin as well, who revealed only a subclinical hypothyroidism. Functional studies of R133W-PAX8 in the HEK293 cells showed activation of the TG promoter comparable to the wild-type PAX8. CONCLUSIONS: In vitro data do not prove that R133W-PAX8 is directly involved in the development of the thyroid phenotypes reported for family members carrying the substitution. However, it is reasonable to conceive that, in the cases of transcriptions factors, such as Pax8, which establish several interactions in different protein complexes, genetic variants could have an impact in vivo.

Presence in the pre-surgical fine-needle aspiration of potential thyroid biomarkers previously identified in the post-surgical one.

Fine-needle aspiration biopsy (FNA) is usually applied to distinguish benign from malignant thyroid nodules. However, cytological analysis cannot always allow a proper diagnosis. We believe that the improvement of the diagnostic capability of pre-surgical FNA could avoid unnecessary thyroidectomy. In a previous study, we performed a proteome analysis to examine FNA collected after thyroidectomy. With the present study, we examined the applicability of these results on pre-surgical FNA. We collected pre-surgical FNA from 411 consecutive patients, and to obtain a correct comparison with our previous results, we processed only benign (n=114), papillary classical variant (cPTC) (n=34) and papillary tall cell variant (TcPTC) (n=14) FNA. We evaluated levels of five proteins previously found up-regulated in thyroid cancer with respect to benign nodules. ELISA and western blot (WB) analysis were used to assay levels of L-lactate dehydrogenase B chain (LDHB), Ferritin heavy chain, Ferritin light chain, Annexin A1 (ANXA1), and Moesin in FNA. ELISA assays and WB analysis confirmed the increase of LDHB, Moesin, and ANXA1 in pre-surgical FNA of thyroid papillary cancer. Sensitivity and specificity of ANXA1 were respectively 87 and 94% for cPTC, 85 and 100% for TcPTC. In conclusion, a proteomic analysis of FNA from patients with thyroid nodules may help to distinguish benign versus malignant thyroid nodules. Moreover, ANXA1 appears to be an ideal candidate given the high sensitivity and specificity obtained from ROC curve analysis.

Iodine fortification of vegetables improves human iodine nutrition: in vivo evidence for a new model of iodine prophylaxis.

BACKGROUND: Iodine deficiency is the result of insufficient intake of dietary iodine and as a consequence causes multiple adverse effects. About 2 billion individuals in the world are affected by iodine deficiency. It has been found that the most effective way to control iodine deficiency is through the universal salt iodization. However, salt iodization alone may not be sufficient to assure adequate iodine nutrition. In most industrialized countries, excess consumption of salt has become recognized as a health risk. Therefore, biofortification of vegetables with iodine offers an excellent opportunity to increase iodine intake. AIM AND METHODS: The aim of this study was to test the efficiency of a new model of iodine prophylaxis in a group of 50 healthy volunteers through the intake of vegetables (potatoes, cherry tomatoes, carrots, and green salad) fortified with iodine. Each serving of vegetables consisted of 100 g of potatoes, carrots, tomatoes, or salad containing 45 mg of iodine (30% of the Recommended Daily Allowance), and the volunteers consumed a single serving of vegetables, as preferred, each day for 2 weeks. Urinary iodine (UI) excretion was measured before and after intake of vegetables. RESULTS: The UI concentration measured in volunteers before the intake of vegetables was 98.3 mg/L (basal value), increasing to 117.5 mg/L during the intake of vegetables. Seven days after the discontinuation of vegetable intake, UI was 85 mg/L. UI concentration increment was 19.6% compared with the basal value; therefore, the difference was statistically significant (P = .035). CONCLUSIONS: Biofortification of vegetables with iodine provides a mild but significative increase in UI concentration and, together with the habitual use of iodized salt, may contribute to improve the iodine nutritional status of the population without risks of iodine excess.

Congenital hypothyroidism caused by a novel homozygous mutation in the thyroglobulin gene.

UNLABELLED: Congenital hypothyroidism (CH) due to thyroglobulin (TG) deficit is an autosomal recessive disease (OMIM #274700) characterized by hypothyroidism, goiter, low serum TG, and a negative perchlorate discharge test. The aim of this study was to perform the genetic analysis of the TG gene in two sisters born from consanguineus parents and affected by CH and low serum TG levels. The index patient and her sister were identified at neonatal screening for CH and treated with L-thyroxine (L-T4). After discontinuation of L-T4 therapy, hypothyroidism was confirmed, serum TG was undetectable, and no organification defect after (123)I scintigraphy and perchlorate test was shown; thyroid ultrasound showed a eutopic gland of normal size. DNA was extracted from peripheral white blood cells of the two sisters and the father. All 48 exons of TG gene were amplified by polymerase chain reaction and subjected to direct sequencing. A novel homozygous point mutation in exon 10 of TG gene was identified in the patient and her sister. The mutation determined a stop codon at position 768 (R768X) resulting in an early truncated protein or in the complete absence of the protein. The father (euthyroid) was heterozygous carrier of the mutation. CONCLUSION: Genetic analysis of TG gene was performed in two sisters affected by CH. A novel point mutation of the TG gene determining a stop codon at position 768 of the protein was identified. The early truncated nonfunctioning protein or the absence of the protein due to the premature degradation of abnormal mRNA may be responsible of the observed phenotype.

Non-autoimmune subclinical hypothyroidism due to a mutation in TSH receptor: report on two brothers.

Subclinical hypothyroidism (SH) is a condition characterized by a mild persistent thyroid failure. The main cause is represented by autoimmune thyroiditis, but mutations in genes encoding proteins involved in TSH pathway are thought to be responsible for SH, particularly in cases arising in familial settings. Patients with the syndrome of TSH unresponsiveness may have compensated or overt hypothyroidism with a wide spectrum of clinical and morphological alterations depending on the degree of impairment of TSH-receptor (TSH-R) function. We describe the case of two brothers with non autoimmune SH carrying the same heterozygous mutation in the extracellular domain of TSH-R and presenting with different clinical, biochemical and morphological features. The first one had only a slight persistent elevation of TSH, a normal thyroid ultrasound and did never require l- thyroxine (L-T4) replacement treatment. The second one had a neonatal persistent moderate TSH levels increase associated with a thyroid gland hypoplasia and was treated with L-T4 since the first months of life.These two cases support the recent association of TSH-R mutations inheritance as an autosomal dominant pattern with variable expressivity and suggest that the decision to start replacement therapy in patients with persistent SH due to TSH resistance should be individualized.

Clinical characteristics and genetic analysis in women with premature ovarian insufficiency.

OBJECTIVE: Premature ovarian insufficiency (POI) is defined as a primary ovarian defect characterized by absent menarche (primary amenorrhea) or premature depletion of ovarian follicles before the age of 40 (secondary amenorrhea) with hypergonadotropism and hypoestrogenism. METHODS: We studied the clinical, biological, and genetic data related to 50 POI patients with a mean age of menopause of 29 years (94% with secondary amenorrhea, 6% with primary amenorrhea and 15% with a family history of POI). Seventeen patients were affected by endocrine autoimmune diseases, antral follicles were observed in 31 patients by ultrasonography. RESULTS: Karyotype analysis did not show any abnormality of the X chromosome. No mutation in FSH receptor and GDF-9 genes was reported, while in one patient a variant of BMP-15 gene (A180T) was found. Four patients had fragile X mental retardation 1 gene (FMR1) premutation and one an intermediate sized CGG repeats of the same gene. Two patients with FMR1 premutation were sister and developed secondary amenorrhea at the age of 34 and 37 years. The other two patients presented with oligoamenorrhea at the age of 39 and 34 years. The patient harboured the intermediate sized CGG repeats developed secondary amenorrhea at the age of 33 years. CONCLUSIONS: The genetic analysis performed on a cohort of patients with POI revealed that 8% had FMR1 premutation and only one patient a previously known variant of BMP-15 gene. No alteration of the karyotype and FSH receptor and GDF-9 genes was evidenced.

MicroRNA expression profile helps to distinguish benign nodules from papillary thyroid carcinomas starting from cells of fine-needle aspiration.

OBJECTIVE: MicroRNAs (miRNAs) are small endogenous noncoding RNAs that pair with target messengers regulating gene expression. Changes in miRNA levels occur in thyroid cancer. Fine-needle aspiration (FNA) with cytological evaluation is the most reliable tool for malignancy prediction in thyroid nodules, but cytological diagnosis remains undetermined for 20% of nodules. DESIGN: In this study, we evaluated the expression of seven miRNAs in benign nodules, papillary thyroid carcinomas (PTCs), and undetermined nodules at FNA. METHODS: The prospective study included 141 samples obtained by FNA of thyroid nodules from 138 patients. miRNA expression was evaluated by quantitative RT-PCR and statistical analysis of data was performed. Genetic analysis of codon 600 of BRAF gene was also performed. RESULTS: Using data mining techniques, we obtained a criterion to classify a nodule as benign or malignant on the basis of miRNA expression. The decision model based on the expression of miR-146b, miR-155, and miR-221 was valid for 86/88 nodules with determined cytology (97.73%), and adopting cross-validation techniques we obtained a reliability of 78.41%. The prediction was valid for 31/53 undetermined nodules with 16 false-positive and six false-negative predictions. The mutated form V600E of BRAF gene was demonstrated in 19/43 PTCs and in 1/53 undetermined nodules. CONCLUSIONS: The expression profiles of three miRNAs allowed us to distinguish benign from PTC starting from FNA. When the assay was applied to discriminate thyroid nodules with undetermined cytology, a low sensitivity and specificity despite the low number of false-negative predictions was obtained, limiting the practical interest of the method.

Metabolic engineering of the iodine content in Arabidopsis.

Plants are a poor source of iodine, an essential micronutrient for human health. Several attempts of iodine biofortification of crops have been carried out, but the scarce knowledge on the physiology of iodine in plants makes results often contradictory and not generalizable. In this work, we used a molecular approach to investigate how the ability of a plant to accumulate iodine can be influenced by different mechanisms. In particular, we demonstrated that the iodine content in Arabidopsis thaliana can be increased either by facilitating its uptake with the overexpression of the human sodium-iodide symporter (NIS) or through the reduction of its volatilization by knocking-out HOL-1, a halide methyltransferase. Our experiments show that the iodine content in plants results from a balance between intake and retention. A correct manipulation of this mechanism could improve iodine biofortification of crops and prevent the release of the ozone layer-threatening methyl iodide into the atmosphere.

Sporadic congenital nonautoimmune hyperthyroidism caused by P639S mutation in thyrotropin receptor gene.

Germline mutations of thyrotropin receptor (TSHR) gene determining a constitutive activation of the receptor were identified as a molecular cause of familial or sporadic congenital nonautoimmune hyperthyroidism (OMIM: 609152) (Nat Genet 7:396-401, 1994; N Engl J Med 332:150-154, 1995; Acta Endocrinol (Copenh) 100:512-518, 1982). We report the case of an Italian child subjected to the first clinical investigation at 24 months for an increased growth velocity; biochemical investigation showed high FT4 and FT3 serum values and undetectable thyrotropin in the absence of anti-thyroid antibodies; the thyroid gland was normal at ultrasound examination. Treatment with methimazole was started at the age of 30 months when her growth velocity was high and the bone age was advanced. DNA was extracted from her parents', brother's, and the patient's blood. Exons 9 and 10 of the TSHR gene were amplified by polymerase chain reaction and subjected to direct sequencing. In proband, a heterozygous substitution of cytosine to thymine determining a proline to serine change at position 639 (P639S) of the TSHR was detected while the parents and brothers of the propositus, all euthyroid, showed only the wild-type sequence of the TSHR gene. This mutation was previously described as somatic in patients affected by hyperfunctioning thyroid nodules and as germline in a single Chinese family affected by thyrotoxicosis and mitral valve prolapse. This constitutively activating mutation is able to activate both the cyclic AMP and the inositol phosphate metabolic pathways when expressed in a heterologous system. In conclusion, we describe the first case of sporadic congenital nonautoimmune hyperthyroidism caused by de novo germinal P639S mutation of TSHR.

Identification and functional analysis of novel dual oxidase 2 (DUOX2) mutations in children with congenital or subclinical hypothyroidism.

CONTEXT: Congenital hypothyroidism (CH) associated with goiter or a gland of normal size has been linked to dual oxidase 2 (DUOX2) mutations in the presence of iodide organification defect. OBJECTIVE: Thirty unrelated children with CH or subclinical hypothyroidism (SH) identified during infancy with a eutopic thyroid gland, coming from our Screening Centre for CH or referred from other regions of Italy, were studied with the perchlorate discharge test to identify organification defects. Eleven children with iodide organification defect were considered for the genetic analysis of TPO, DUOX2, and dual oxidase maturation factor 2 (DUOXA2) genes. PATIENTS: Eight children with CH and three with SH and eutopic thyroid gland were included in the study. After discontinuation of therapy, a partial or complete organification defect was shown after ¹²³I scintigraphy and perchlorate test. METHODS: TPO, DUOX2, and DUOXA2 genes were analyzed, and functional activity of DUOX2 variants was studied in HeLa cells. RESULTS: Sequencing of the DUOX2 gene revealed a deletion S965fsX994 in three children; two were euthyroid after 1 month of L-T4 discontinuation but developed SH after 5 and 18 months, respectively, whereas the other child had SH. One child with SH showed H678R, R701Q, and P982A substitutions, and another child with SH showed only the P982A. One child with SH showed the Y1150C mutation, and another euthyroid child showed the A728T mutation. Functional studies confirmed that S965fsX994, Y1150C, and A728T mutations were responsible for the defect in H2O2 production, whereas H678R, R701Q, and P982A did not alter H2O2 production in vitro. CONCLUSIONS: Genetic analysis of the DUOX2 gene was performed in 11 children with organification defect. Two new mutations (Y1150C and A728T) and the deletion S965FsX994 were responsible for the deficit in the organification process and the phenotypes. Three polymorphisms (H678R, P982A, and R701Q) were identified.

3-Iodothyronamine metabolism and functional effects in FRTL5 thyroid cells.

3-Iodothyronamine (T(1)AM), produced from thyroid hormones (TH) through decarboxylation and deiodination, is a potent agonist of trace amine-associated receptor 1 (TAAR1), a G protein-coupled receptor belonging to the family of TAARs. In vivo T(1)AM induces functional effects opposite to those produced on a longer time scale by TH and might represent a novel branch of TH signaling. In this study, we investigated the action of T(1)AM on thyroid and determined its uptake and catabolism using FRTL5 cells. The expression of TAAR1 was determined by PCR and western blot in FRTL5 cells, and cAMP, iodide uptake, and glucose uptake were measured after incubation with increasing concentrations of T(1)AM for different times. T(1)AM and its catabolites thyronamine (T(0)AM), 3-iodothyroacetic acid (TA(1)), and thyroacetic acid (TA(0)) were analyzed in FRTL5 cells by HPLC coupled to tandem mass spectrometry. The product of amplification of TAAR1 gene and TAAR1 protein was demonstrated in FRTL5 cells. No persistent and dose-dependent response to T(1)AM was observed after treatment with increasing doses of this substance for different times in terms of cAMP production and iodide uptake. A slight inhibition of glucose uptake was observed in the presence of 100 µM T(1)AM after 60 and 120 min (28 and 32% respectively), but the effect disappeared after 18 h. T(1)AM was taken up by FRTL5 cells and catabolized to T(0)AM, TA(1), and TA(0) confirming the presence of deiodinase and amine oxidase activity in thyroid. In conclusion, T(1)AM determined a slight inhibition of glucose uptake in FRTL5 cells, but it was taken up and catabolized by these cells.

Congenital hypothyroidism and late-onset goiter: identification and characterization of a novel mutation in the sodium/iodide symporter of the proband and family members.

BACKGROUND: Iodide transport defects (ITDs), rare causes of congenital hypothyroidism (CH), have been shown to arise from abnormalities of the sodium/iodide symporter (NIS). We describe a 16-year-old girl with CH caused by an ITD resulting from a novel mutation of NIS. SUMMARY: A 16-year-old girl with CH diagnosed by a neonatal screening program received early treatment with L-thyroxine replacement therapy. A (123)I scan had failed to reveal any iodide uptake by the thyroid and salivary glands; thus, thyroid agenesis was diagnosed. Thyroglobulin (Tg) was not measured when she was a neonate or infant. Unexpectedly, at the age of 14.5 years, a nodular goiter and high serum Tg concentrations (303 ng/mL; normal, <50) were identified. Her thyroid radioactive iodine uptake was very low as was the saliva to plasma iodide ratio (0.5). Analysis of her NIS gene revealed an in-frame six-nucleotide deletion of the coding sequence (1206-1211delGTCGGC) corresponding to the deletion of amino acids 287 and 288 of the human NIS protein located at the beginning of the VIII transmembrane segment. The proband was homozygous for this deletion, whereas both unrelated parents and her brother were heterozygous. COS-7 cells transfected with the mutant NIS failed to concentrate iodide, confirming that the mutation was the direct cause of the ITD in this patient. CONCLUSIONS: We describe a patient with CH caused by a previously not described mutation of the NIS gene that was inherited from her parents. We therefore recommend that thyroid ultrasonography be performed in CH patients with low radioactive iodine uptake and elevated serum Tg.

Identification and functional studies of two new dual-oxidase 2 (DUOX2) mutations in a child with congenital hypothyroidism and a eutopic normal-size thyroid gland.

CONTEXT: Some cases of congenital hypothyroidism (CH) are associated with a gland of normal size. OBJECTIVE: To explore the cause of organification defect in one child with CH and a eutopic thyroid gland, genetic analyses of TPO, DUOX2, and DUOXA2 genes were performed. PATIENT: One child with CH, a eutopic thyroid gland, and a partial organification defect was shown after (123)I scintigraphy and perchlorate test. METHODS: In the child with the organification defect, TPO, DUOX2, and DUOXA2 genes were analyzed. The functional activity of the DUOX2 mutants was studied after expression in eukaryotic cells. RESULTS: No TPO or DUOXA2 gene mutations were identified. Direct sequencing of the DUOX2 gene revealed a compound heterozygous genotype for S911L and C1052Y substitutions. S911L and C1052Y caused a partial defect in H(2)O(2) production after transient expression in HeLa cells. CONCLUSIONS: We performed a genetic analysis in one child with CH and a eutopic thyroid gland. Two new mutations in DUOX2 gene responsible for the partial deficit in the organification process were identified.