Mutations in the iodotyrosine deiodinase gene and hypothyroidism.

DEHAL1 has been identified as the gene encoding iodotyrosine deiodinase in the thyroid, where it controls the reuse of iodide for thyroid hormone synthesis. We screened patients with hypothyroidism who had features suggestive of an iodotyrosine deiodinase defect for mutations in DEHAL1. Two missense mutations and a deletion of three base pairs were identified in four patients from three unrelated families; all the patients had a dramatic reduction of in vitro activity of iodotyrosine deiodinase. Patients had severe goitrous hypothyroidism, which was evident in infancy and childhood. Two patients had cognitive deficits due to late diagnosis and treatment. Thus, mutations in DEHAL1 led to a deficiency in iodotyrosine deiodinase in these patients. Because infants with DEHAL1 defects may have normal thyroid function at birth, they may be missed by neonatal screening programs for congenital hypothyroidism.

CD73 expression in normal, hyperplastic, and neoplastic thyroid: a systematic evaluation revealing CD73 overexpression as a feature of papillary carcinomas.

CD73 converts AMP to adenosine, an immunosuppressive metabolite that promotes tumorigenesis. This study presents a systematic evaluation of CD73 expression in benign, hyperplastic, and neoplastic thyroid. CD73 expression was assessed by immunohistochemistry in 142 thyroid samples. CD73 was expressed in normal thyroid (3/6) and goiter (5/6), with an apical pattern and mild intensity. Apical and mild CD73 expression was also present in oncocytic cell adenomas/carcinomas (9/10; 5/8) and in follicular adenomas/carcinomas (12/18; 23/27). In contrast, papillary thyroid carcinomas featured extensive and intense CD73 staining (49/50) (vs. normal thyroid/goiter, p < 0.001). Seven of nine anaplastic carcinomas were CD73-positive with heterogeneous extensiveness of staining. Medullary and poorly differentiated carcinomas were mostly CD73-negative (1/6; 2/2). These results were corroborated by NT5E mRNA profiling. Papillary carcinomas feature enhanced CD73 protein and mRNA expression with distinct and intense staining, more pronounced in the invasive fronts of the tumors.

Lack of complex I is associated with oncocytic thyroid tumours.

Oncocytic tumours are characterised by hyperproliferation of mitochondria. We immunohistochemically analysed all enzymes of the oxidative phosphorylation system in 19 oncocytic thyroid tumours. A specific lack of complex I was detected, which was expressed at <5% of the level determined in surrounding non-cancerous tissue.

Pten loss in the mouse thyroid causes goiter and follicular adenomas: insights into thyroid function and Cowden disease pathogenesis.

Inactivation and silencing of the tumor suppressor PTEN are found in many different epithelial tumors, including thyroid neoplasia. Cowden Disease patients, who harbor germ-line PTEN mutations, often display thyroid abnormalities, including multinodular goiter and follicular adenomas, and are at increased risk of thyroid cancer. To gain insights into the role PTEN plays in thyroid function and disease, we have generated a mouse strain, in which Cre-mediated recombination is used to specifically delete Pten in the thyrocytes. We found that Pten mutant mice develop diffuse goiter characterized by extremely enlarged follicles, in the presence of normal thyroid-stimulating hormone and T4 hormone levels. Loss of Pten resulted in a significant increase in the thyrocyte proliferative index, which was more prominent in the female mice, and in increased cell density in the female thyroid glands. Surprisingly, goitrogen treatment did not cause a substantial increase of the mutant thyroid size and increased only to some extent the proliferation index of the female thyrocytes, suggesting that a relevant part of the thyroid-stimulating hormone-induced proliferation signals are funneled through the phosphatidylinositol-3-kinase (PI3K)/Akt cascade. Although complete loss of Pten was not sufficient to cause invasive tumors, over two thirds of the mutant females developed follicular adenomas by 10 months of age, showing that loss of Pten renders the thyroid highly susceptible to neoplastic transformation through mechanisms that include increased thyrocyte proliferation. Our findings show that constitutive activation of the PI3K/Akt cascade is sufficient to stimulate continuous autonomous growth and provide novel clues to the pathogenesis of Cowden Disease and sporadic nontoxic goiter.

Pseudodominant inheritance of goitrous congenital hypothyroidism caused by TPO mutations: molecular and in silico studies.

CONTEXT AND OBJECTIVE: Most cases of goitrous congenital hypothyroidism (CH) from thyroid dyshormonogenesis 1) follow a recessive mode of inheritance and 2) are due to mutations in the thyroid peroxidase gene (TPO). We report the genetic mechanism underlying the apparently dominant inheritance of goitrous CH in a nonconsanguineous family of French Canadian origin. DESIGN, SETTING, AND PARTICIPANTS: Two brothers identified by newborn TSH screening had severe hypothyroidism and a goiter with increased (99m)Tc uptake. The mother was euthyroid, but the father and two paternal uncles had also been diagnosed with goitrous CH. After having excluded PAX8 gene mutations, we hypothesized that the underlying defect could be TPO mutations. RESULTS: Both compound heterozygous siblings had inherited a mutant TPO allele carried by their mother (c.1496delC; p.Pro499Argfs2X), and from their father, one brother had inherited a missense mutation (c.1978C-->G; p.Gln660Glu) and the other an insertion (c.1955insT; p.Phe653Valfs15X). The thyroid gland of one uncle who is a compound heterozygote for TPO mutations (p.Phe653Valfs15X/p.Gln660Glu) was removed because of concurrent multiple endocrine neoplasia type 2A. Immunohistochemistry revealed normal TPO staining, implying that Gln660Glu TPO is expressed properly. Modeling of this mutant in silico suggests that its three-dimensional structure is conserved, whereas the electrostatic binding energy between the Gln660Glu TPO and its heme group becomes repulsive. CONCLUSION: We report a pedigree presenting with pseudodominant goitrous CH due to segregation of three different TPO mutations. Although goitrous CH generally follows a recessive mode of inheritance, the high frequency of TPO mutations carriers may lead to pseudodominant inheritance.

Studies on the goitrogenic mechanism of action of N,N,N',N'-tetramethylthiourea.

N,N,N',N'-Tetramethylthiourea (TMTU) is a rat goitrogen inducing thyroid hyperplasia, hypertrophy, and tumor formation. Little is known about the exact underlying mechanism of action. As thyroid peroxidase (TPO) and type I iodothyronine deiodinase (ID-I) have been established as targets of goitrogenic thiourea derivatives, we investigated interactions of TMTU with target enzymes using a partially purified fraction from hog thyroids or solubilized hog thyroid microsomes and 10,000g supernatant from rat liver homogenate, respectively, as enzyme sources. For comparison, comprehensively characterized goitrogenic thiourea derivatives were studied as well. In contrast to propylthiouracil (PTU), and like ethylenethiourea (ETU), TMTU only marginally affected TPO-catalyzed oxidation of guaiacol. TMTU, like ETU, concentration-dependently suppressed TPO-catalyzed iodine formation with concomitant oxidative metabolism. Suppression ceased upon consumption of thiourea derivatives, the rate of the reappearing iodine formation was similar to that of controls. TMTU, like ETU, also suppressed non-enzymatic and TPO-catalyzed monoiodination of l-tyrosine with a stoichiometry of 2:1, i.e., one molecule of thiourea derivative suppressed two times monoiodination. TMTU and ETU were unable to irreversibly inhibit TPO. In contrast to PTU, TMTU did not inhibit ID-I. These findings provide evidence that TMTU interferes with thyroid hormone synthesis at the level of iodination and demonstrate a metabolic route for the oxidative detoxification of TMTU in the thyroid suggesting that low-level or intermittent exposure to TMTU would have only minimal effects on thyroid hormone synthesis. Finally, it can be concluded that meaningful toxicological studies on TPO inhibition can be performed without a need for highly purified TPO.

Prevalence of c.2268dup and detection of two novel alterations, c.670_672del and c.1186C>T, in the TPO gene in a cohort of Malaysian-Chinese with thyroid dyshormonogenesis.

OBJECTIVES: The c.2268dup mutation in the thyroid peroxidase (TPO) gene is the most common TPO alteration reported in Taiwanese patients with thyroid dyshormonogenesis. The ancestors of these patients are believed to originate from the southern province of China. Our previous study showed that this mutation leads to reduced abundance of the TPO protein and loss of TPO enzyme activity in a Malaysian-Chinese family with goitrous hypothyroidism. The aim of our study was to provide further data on the incidence of the c.2268dup mutation in a cohort of Malaysian-Chinese and its possible phenotypic effects. SETTING: Cohort study. PARTICIPANTS: Twelve biologically unrelated Malaysian-Chinese patients with congenital hypothyroidism were recruited in this study. All patients showed high thyrotropin and low free thyroxine levels at the time of diagnosis with proven presence of a thyroid gland. PRIMARY OUTCOME MEASURE: Screening of the c.2268dup mutation in the TPO gene in all patients was carried out using a PCR-direct DNA sequencing method. SECONDARY OUTCOME MEASURE: Further screening for mutations in other exonic regions of the TPO gene was carried out if the patient was a carrier of the c.2268dup mutation. RESULTS: The c.2268dup mutation was detected in 4 of the 12 patients. Apart from the c.2268dup and a previously documented mutation (c.2647C>T), two novel TPO alterations, c.670_672del and c.1186C>T, were also detected in our patients. In silico analyses predicted that the novel alterations affect the structure/function of the TPO protein. CONCLUSIONS: The c.2268dup mutation was detected in approximately one-third of the Malaysian-Chinese patients with thyroid dyshormonogenesis. The detection of the novel c.670_672del and c.1186C>T alterations expand the mutation spectrum of TPO associated with thyroid dyshormonogenesis.

Five novel inactivating mutations in the thyroid peroxidase gene responsible for congenital goiter and iodide organification defect.

Thyroid peroxidase (TPO) defects, typically transmitted as autosomal recessive traits, result in hypothyroid goiters with failure to convert iodide into organic iodine. We analyzed the TPO gene in 14 unrelated patients with clinical evidence of iodide organification defects. Seven of the affected individuals harbored mutations in the TPO gene; one was compound heterozygous, the others were simply heterozygous for TPO mutations. Five novel mutations have been identified, one of which was found to be a single nucleotide deletion, while the other four were single nucleotide substitutions. A frameshift mutation c.387delC was detected in exon 5 which leads to an early termination signal in exon 7 (p.N129fsX208). Two missense mutations were identified in exon 8. The first, a c.920A>C transversion that results in a p.N307T substitution, was found in two patients. The second, a c.1297G>A transition, results in p.V433M. A c.1496C>T transition was detected in exon 9 that caused the substitution p.P499L. Finally, in exon 14 a c.2422T>C transition was identified, causing a p.C808R change. In addition, the previously reported GGCC duplication in exon 8 (c.1186_1187insGGCC; p.R396fsX472) was also detected in two affected individuals, one of whom was a compound heterozygous (p.R396fsX472/p.V433M).

Defective organification of iodide causing congenital goitrous hypothyroidism.

A 26-yr-old Japanese woman with congenital goitrous hypo-thyroidism and sensorineural deafness underwent a thyroidectomy. Examination of the thyroid gland revealed characteristic features of multinodular goiter. The T3 and T4 content in thyroglobulin (Tg) were 0.03 and 0.02 mol/mol Tg, respectively. Iodide incorporation into Tg, using slices of the thyroid tissue, revealed that iodide organification of thyroid tissue from our patient was markedly lower than that of normal controls. Then, guaiacol and iodide oxidation activities of thyroid peroxidase (TPO) in our patient's thyroid tissue were lower than those of normal controls (guaiacol assay: 1.92 vs. 30.0 +/- 5.7 mGU/mg protein; iodide assay: 1.1 vs. 6.6 +/- 2.8 mIU/mg protein). Lineweaver-Burk plot analysis of the oxidation rates of guaiacol and iodide indicated that this patient's TPO had a defect in the binding of guaiacol and iodide, but the coupling activity of the patient's TPO was not decreased compared with those of two normal thyroids. In this case and in control subjects, Nothern gel analysis of TPO messenger RNA from unstimulated and TSH-stimulated thyroid cells revealed a 3.2 kilobase species in the former and four distinct messenger RNA species of 4.0, 3.2, 2.1, and 1.7 kilobases in the latter. Western blot analysis of TPOs obtained from this patient and from control subjects identified the same 107 kDa protein, using antimicrosomal antibody-positive serum. We analyzed the coding sequence in the patient's TPO gene by using polymerase chain reaction technique. A single point mutation of G-->C at 1265 base pair was detected only in the TPO gene, but this point mutation does not alter the amino acid residue. It is possible that posttranslational modification such as abnormal glycosylation may occur in the TPO molecules. Furthermore, it is possible that there are differences in the tertiary structures of the TPO molecules between our patient and normal subjects. The above abnormalities of TPO molecules may play an important role in our patient's dyshormonogenesis.

Influence of thyroglobulin on basal and stimulated human thyroid adenylate cyclase activity.

The interaction of thyroglobulin (Tg), thyroid-stimulating immunoglobulins (TSI), and TSH on human thyroid plasma membranes from nontoxic goiter was studied in vitro by an adenylate cyclase assay system using human thyroid homogenate. Purified Tg [3 X 10(-10) M (0.2 micrograms/ml) to 3 X 10(-8) M (20 micrograms/ml)] exerted a dose- and time-dependent inhibitory influence on basal adenylate cyclase activity. The inhibition was prevented by preincubation with Tg antibody in excess. Tg (3 X 10(-8) M) caused a significant reduction in the TSH- and TSI-stimulated adenylate cyclase activities, but did not influence stimulation with NaF (8 mM). Fractions of thyroid homogenates were obtained by differential centrifugation, and the maximal inhibitory influence of Tg was located in the 5000 X g fraction. Thus, Tg is an efficient inhibitor of basal and TSH- or TSI- stimulated adenylate cyclase activities, and might be involved in a short loop counterregulation of thyroid adenylate cyclase sensitivity in vivo.

Thyrotrophin and thyroid-stimulating immunoglobulins have similar characteristics in activating human thyroid membrane adenylate cyclase.

The activation of adenylate cyclase by TSH and thyroid-stimulating immunoglobulins (TSIg) was investigated in membranes prepared from non-toxic goitres. The assay conditions for maximal adenylate cyclase stimulation by TSH in the absence and presence of a cell cytosol preparation were determined. Cell cytosol had no detectable effect on the characteristics of activation by TSH although it increased the production of cyclic AMP in response to the hormone. In the presence of cell cytosol, membrane protein, pH and substrate concentration dependency of adenylate cyclase activation by both TSH and TSIg were similar. In a comparison of the time-courses of activation there was no apparent lag phase in the activation of adenylate cyclase by TSIg but the onset of activation was slower and linearity persisted longer than with TSH.

Protein kinase C activity in experimentally developed and regressed rat thyroid goitres.

The presence of protein kinase C activity in rat thyroid glands was demonstrated by kinetic studies, using lysine-rich histone as substrate. DE 52 cellulose chromatography resolved thyroidal protein kinase C activity into two peaks, the first eluting at 50 mM and the second at 150 mM salt solution. They contained respectively 40% and 60% of the total activity. In cytosols from experimentally induced goitres, which are hyperplastic tissues, protein kinase C activity rose 3-4-fold compared to control glands. In this tissue, protein kinase C seems to be present in reversibly activated form, since its activity was completely inhibited in the absence of calcium and phospholipids. After removal of growth stimulus, rapid involution of goitres occurred, producing a spectacular decrease in protein kinase C activity. In goitres regressed for 5 days, the level of protein kinase C was lower than in untreated control tissue. The protein kinase C activities in control glands and developed and regressed goitres were 1.88, 5.85 and 0.74 pmoles 32P/mg tissue, respectively. These results clearly demonstrate, for the first time, a direct correlation between the protein kinase C level and the thyroid gland growth activity induced by endogenous stimuli.

Expression of telomerase genes in thyroid carcinoma.

Telomerase (T) is a ribonucleoprotein complex that includes the telomerase RNA component (hTR), telomerase associated protein (TP1) and the telomerase catalytic subunit (hTERT). Telomerase has been shown in stem cells and found to be activated in tumor tissues and immortalized cells. We wanted to test whether the expression of the telomerase complex subunits correlate with the enzyme activity in human thyroid tissue. Hence, we determined the expression of hTERT, hTR and TP1 mRNA by RT-PCR and compared the results to telomerase activity as detected by the telomeric repeat amplification protocol (TRAP) assay. Fifteen benign goiters (G), 11 follicular carcinomas (FTC) including 2 oncocytic follicular carcinomas (also called Hurthle cell carcinoma, oFTC), 12 papillary carcinomas (PTC) including 3 microcarcinomas (mPTC), and 12 undifferentiated anaplastic thyroid carcinomas (UTC) were investigated. Experienced pathologists performed histological and pTNM classification in each specimen. RT-PCR analysis revealed that TP1 was ubiquitously expressed in all G and carcinomas. hTR was expressed in 4 out of 15 G, in 2 out of 3 mPTC, in 5 out of 9 PTC, in 5 out of 9 FTC, in all oFTC and in 9 out of 12 UTC samples. Regarding all carcinomas, no statistically significant correlation was observed between hTR-expression and tumor stage, lymph node or distant metastasis. hTERT-expression was associated with malignancy and tumor stage. All mPTC and 13 out of 15 G did not express hTERT, whereas all samples of pT3-4 tumor stage of FTC, PTC, UTC and all oFTC were positive for hTERT. No telomerase activity could be detected in G. Telomerase activity in carcinoma was only measurable in tissues that expressed the catalytic subunit hTERT. Our data indicate that telomerase activity is up-regulated in neoplastic cells. In contrast to TP1 and hTR, hTERT and telomerase activity may be of help in identifying invasive tumors and may be additional markers for classification of benign goiter and malignant thyroid carcinoma.

Distribution of the 72-kd type IV collagenase in nonneoplastic and neoplastic thyroid tissue.

The 72-kd type IV collagenase (matrix metalloproteinase-2 [MMP-2]) is a neutral metalloproteinase that initiates the degradation of type IV collagen in basement membranes. Its production by tumor cells has been correlated with the invasive and metastatic potential of neoplasms. Two recently developed affinity-purified antibodies against synthetic peptides from the amino terminus (H1) and an internal domain (Ab48) of the molecule were used to investigate immunohistochemically the distribution of this enzyme in a variety of thyroid tissues. All primary carcinomas (20 papillary, seven follicular, and three medullary) as well as nine of 11 metastases were positive, with the more aggressive tumors (tall cell variant of papillary carcinomas and invasive follicular carcinomas) tending to be more reactive than the low-grade tumors (classic and microinvasive papillary carcinomas and minimally invasive follicular tumors). Negative or minimal positivity was found in six cases of normal thyroid, one goiter, and two cases of Graves' disease. Immunoreactive follicular cells were seen focally in areas of inflammation, fibrosis, and distortion of normal follicles, and in Hashimoto's thyroiditis (four cases). Five of nine adenomas showed positive cells, but this could be related to previous trauma to the area. We conclude that there is increased production of the 72-kd type IV collagenase (MMP-2) in thyroid cancer; however, this enzyme also is elevated in benign conditions that are undergoing remodeling and repair.

Immunohistochemical localization of inducible and endothelial constitutive nitric oxide synthase in neoplastic and autoimmune thyroid disorders.

AIM: To investigate the distribution of nitric oxide synthase in tissues derived from patients with autoimmune or neoplastic disorders of the thyroid gland in order to test whether the expression of inducible nitric oxide synthase or endothelial constitutive nitric oxide synthase (two subtypes of EC 1.14.13.39) may be related to the inflammatory activity or degree of neoplasia. EXPERIMENTAL DESIGN: The expression of nitric oxide synthases was examined by immunohistochemistry in tissues from patients with either Hashimoto's thyroiditis (n=6), hyperplastic glands (Graves' disease) (n=7), adenomas (n=8), multinodular goitres (n=7), papillary carcinomas (n=4) or follicular carcinomas (n=5). RESULTS: Expression of inducible nitric oxide synthase was found in 22 of the tissues and was not specific for any of the examined thyroid disorders. Expression of endothelial constitutive nitric oxide synthase was found in some of the epithelial cells in all the tissues. There was no correlation between the intensity and distribution of the immunostaining and the thyroid disorders. CONCLUSION: Demonstration of nitric oxide synthase cannot be used for diagnostic purposes. The expression of endothelial constitutive nitric oxide synthase in all tissues indicates that the enzyme may be of importance for the function or growth of the thyroid epithelial cells.

Thyroid-stimulating hormone activates phospholipase C in normal and neoplastic thyroid tissue.

BACKGROUND: Thyroid-stimulating hormone (TSH) stimulates thyroid growth through two signal transduction pathways: the G protein-adenylate cyclase system and the G protein-phospholipase C (PLC) system. The adenylate cyclase system has been studied extensively, but there is little information available concerning PLC activity in thyroid neoplasms. METHODS: Human thyroid membranes were incubated for 30 minutes at 37 degrees C in the presence or absence of bovine TSH (300 mU/ml). PLC activity was assayed by liberation of inositol phosphates from the enzymatic hydrolysis of tritiated phosphatidylinositol bisphosphate. Fifty-six tissues were assayed (normal, 23; multinodular goiter, 5; follicular adenoma, 9; and differentiated thyroid cancer, 19 [9 low risk and 10 high risk]). RESULTS: TSH significantly increased PLC activity in normal, benign, and most malignant thyroid neoplasms. Although there were no differences in basal or TSH-stimulated PLC activity between the groups of normal thyroid, multinodular goiter, follicular adenoma, or the cancers, one half of the high-risk cancers had an aberrant PLC response. CONCLUSIONS: This is the first demonstration that TSH stimulates PLC activity in normal and neoplastic human thyroid tissue. Aberrant TSH-stimulated PLC activity was present in half of the aggressive thyroid neoplasms.

Differentiation of two abnormalities in thyroid peroxidase causing organification defect and goitrous hypothyroidism.

Clinical and laboratory evaluations are reported on two patients with congenital goiter and hypothyroidism due to iodide organification defect. In one patient, a 31-year-old white male with severe mental retardation, administration of perchlorate caused discharge of 69% of the radioiodine accumulated in the thyroid gland. Thyroid tissue had negligible peroxidase activity in the tyrosine-iodinase, triliodide, and guaiacol assays. Preincubation of subcellular fractions with hematin restored activity. The restored enzyme was labile to high concentrations of H2O2 (5.6times 10-4 h2o2 produced inhibition in the triiodide assay). Heating of the enzyme for 5 min at 46 degrees C produced 50% inactivation, while higher temperatures were required to half-inactivate normal peroxidases. This case represents a second example of the "peroxidase apoenzyme-prosthetic group defect" causing congenital goiter. The second patient, an example of the "deficient peroxidase defect," was a 10-yr-old girl with 35% discharge of thyroidal radioiodine by perchlorate. Peroxidase activity in the goiter tissue was quantitatively decreased (10%-20% of normal values) but kinetically normal with respect to apparent Km for H2O2. Hematin had little effect on the enzyme. Peroxidase activity had abnormal subcellular distribution, since pellets sedimenting between 39,000 and 105,000 g contained most of the activity. Normal thyroglobulin was observed in the thyroid gland of the patient. Two distinct defects of the peroxidase system can produce congenital goiter by limiting organification of iodide.

Deficient cytochrome b5 reductase activity in nontoxic goiter with iodide organification defect.

A 37-yr-old woman with nontoxic goiter is presented. The thyroid 131I uptake at 3 and 24 hr were, respectively, 77.1% and 81.4% dose. Thiocyanate discharged 65.5% of the accumulated 131I in 30 min. In vitro organification of iodine in the thyroid homogenate from the patient was impaired and it was restored to normal by the addition of H2O2, glucose, and glucose oxidase system, FAD, or reduced cytochrome b5. Riboflavin, FMN, oxidized cytochrome b5, oxidized or reduced cytochrome c, NAD(H), and NADP(H) were ineffective in the reaction. The microsomal NADH-cytochrome b5 reductase activity was definitely low in the patient's thyroid. It was augmented to a normal level by incubation of the microsomes with FAD for 30 min or more. The activities of thyroid peroxidase, G6-PD, 6-PGD, catalase, protease, and NADPH-cytochrome c reductase were within normal limits. The major thyroid protein was normal thyroglobulin which could be readily iodinated in the presence of H2O2 and horse radish peroxidase. These findings suggest the correlation of an iodide organification defect with a cytochrome b5 reductase deficiency. Administration of high doses of FAD led to the restoration of thyroidal iodide organification mechanism associated with an increased thyroid hormone production and to a marked decrease of the goiter. Riboflavin was given without effect even at a high dosage level. Consequently, it seems likely that the deficient cytochrome b5 reductase activity in this patient is due to a defect in the biosynthesis of FAD, the coenzyme of the reductase, from riboflavin.

Catecholamine-thyroid hormone interactions: II. Thyroid hormone and platelet MAO activity in patients with thyroid disorders.

Platelet monoamine oxidase (MAO) activity and serum thyroxine indices were determined in 62 children and adolescents currently undergoing medical treatment for various thyroid disorders. The platelet MAO activity of these patients was similar to that of control and contrast groups previously reported, and there were no differences when patients were grouped according to specific thyroid disorders. Estimated free thyroxine and total thyroxine levels were generally in the upper normal or slightly elevated range and were not significantly related to MAO activity.

Thyroid peroxidase in dyshormonogenetic goiters with organification and thyroglobulin defects.

Thyroid peroxidase (TPO) iodide and guaiacol oxidation activities were evaluated in eight dyshormonogenetic goiters. Two of these had a defective thyroglobulin; the TPO iodide oxidation (431 and 316 U/g ptn) and iodination (31 and 8.6 nmol I/mg ptn) activities were within the normal ranges. The goiters from two siblings with positive perchlorate iodide discharge tests also had normal TPO iodide oxidation (602 and 299 U/g ptn) and iodination activities (44 and 11 nmol I/mg ptn). No TPO iodide oxidation activity was found in the goiters from the other four patients with positive perchlorate iodide discharge tests, and TPO iodide oxidation inhibitory activities were detected in both their TPO and thyroglobulin preparations. Three of them had some TPO guaiacol oxidation activity and did not inhibit normal guaiacol oxidation. The TPO preparation immunoblot of these three goiters showed a faintly visible band of normal 100 kDa TPO. However, in the other patient no guaiacol oxidation activity was detected, and only two bands of low-molecular-weight TPO (72 and 43 kDa) were found, again showing that iodine organification defects in dyshormonogenetic goiters can be due to either qualitative or quantitative TPO defects. The TPO inhibition diminished when iodide was increased in the assay, but was not altered by increasing cofactor (H2O2). Our results, so far, suggest that the TPO-inhibitory substance may interact reversibly with a specific iodide site on the enzyme or with the oxidized form of iodide, and/or could bind free iodide, making it unavailable for enzymatic oxidation.