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      Congenital hyperthyroidism: the fetus as a patient.

      Hormone research
      Female, Fetal Diseases, diagnosis, etiology, therapy, Humans, Hyperthyroidism, congenital, Infant, Newborn, Male, Pregnancy

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          Abstract

          Congenital hyperthyroidism is less frequent than congenital hypothyroidism but its impact on growth and development can be as dramatic. The immune form of hyperthyroidism that is transmitted from a mother with Graves' disease to her foetus and then neonate is transient, but cases of persistent congenital hyperthyroidism had also been described, that can now be explained by molecular abnormalities of the thyrotropin receptor. The abundance of published data on the neonatal effects of maternal Graves' disease contrasts with the paucity of information on fetal effects. Recent studies showed that it is of utmost to scrutinize fetal thyroid by expert ultrasonographist and to have a team work with obstetricians and pediatric endocrinologists in pregnant women with Graves' disease. This allowed to accurately determine the fetal thyroid status and to adapt the treatment in the mothers successfully. Fetal hyperthyroidism does exist and needs an appropriate aggressive treatment. Clearly the fetus has become our patient!

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          Most cited references29

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          Thyroid development and its disorders: genetics and molecular mechanisms.

          Thyroid gland organogenesis results in an organ the shape, size, and position of which are largely conserved among adult individuals of the same species, thus suggesting that genetic factors must be involved in controlling these parameters. In humans, the organogenesis of the thyroid gland is often disturbed, leading to a variety of conditions, such as agenesis, ectopy, and hypoplasia, which are collectively called thyroid dysgenesis (TD). The molecular mechanisms leading to TD are largely unknown. Studies in murine models and in a few patients with dysgenesis revealed that mutations in regulatory genes expressed in the developing thyroid are responsible for this condition, thus showing that TD can be a genetic and inheritable disease. These studies open the way to a novel working hypothesis on the molecular and genetic basis of this frequent human condition and render the thyroid an important model in the understanding of molecular mechanisms regulating the size, shape, and position of organs.
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            Maternal-fetal transfer of thyroxine in congenital hypothyroidism due to a total organification defect or thyroid agenesis.

            The fact that neonates who subsequently have severe hypothyroidism have no evidence of the condition at birth suggests the possibility of the placental transfer of thyroid hormones. Recent studies have demonstrated the existence of such transfer in hypothyroid rats. To determine whether there is a transfer of thyroxine (T4) from mother to fetus, we studied 25 neonates born with a complete inability to iodinate thyroid proteins and therefore to synthesize T4. This total organification defect is an autosomal recessive disorder with an incidence of approximately 1 in 60,000 neonates in the Netherlands. In the cord serum of affected neonates, T4 levels ranged from 35 to 70 nmol per liter. Since these patients were unable to produce any T4, the T4 must have originated in their mothers. The estimated biologic half-life of serum T4 was 3.6 days (95 percent confidence interval, 2.7 to 5.3). In 15 neonates with thyroid agenesis, the serum levels and the disappearance kinetics of T4 were the same as those in the neonates with a total organification defect, suggesting that in these infants, the T4 also had a maternal origin. We conclude that in infants with severe congenital hypothyroidism, substantial amounts of T4 are transferred from mother to fetus during late gestation.
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              Thyrotropin receptor-associated diseases: from adenomata to Graves disease.

              The thyroid-stimulating hormone receptor (TSHR) is a G protein-linked, 7-transmembrane domain (7-TMD) receptor that undergoes complex posttranslational processing unique to this glycoprotein receptor family. Due to its complex structure, TSHR appears to have unstable molecular integrity and a propensity toward over- or underactivity on the basis of point genetic mutations or antibody-induced structural changes. Hence, both germline and somatic mutations, commonly located in the transmembrane regions, may induce constitutive activation of the receptor, resulting in congenital hyperthyroidism or the development of actively secreting thyroid nodules. Similarly, mutations leading to structural alterations may induce constitutive inactivation and congenital hypothyroidism. The TSHR is also a primary antigen in autoimmune thyroid disease, and some TSHR antibodies may activate the receptor, while others inhibit its activation or have no influence on signal transduction at all, depending on how they influence the integrity of the structure. Clinical assays for such antibodies have improved significantly and are a useful addition to the investigative armamentarium. Furthermore, the relative instability of the receptor can result in shedding of the TSHR ectodomain, providing a source of antigen and activating the autoimmune response. However, it may also provide decoys for TSHR antibodies, thus influencing their biological action and clinical effects. This review discusses the role of the TSHR in the physiological and pathological stimulation of the thyroid.
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                Author and article information

                Journal
                16582565
                10.1159/000092454

                Chemistry
                Female,Fetal Diseases,diagnosis,etiology,therapy,Humans,Hyperthyroidism,congenital,Infant, Newborn,Male,Pregnancy

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