Hyperthyroidism in pregnancy

Chromatin remodellers Brg1 and Bptf are required for normal gene expression and progression of oncogenic Braf-driven mouse melanoma

Somatic oncogenic mutation of BRAF coupled with inactivation of PTEN constitute a frequent combination of genomic alterations driving the development of human melanoma. Mice genetically engineered to conditionally express oncogenic Braf^V600E and inactivate Pten in melanocytes following tamoxifen treatment rapidly develop melanoma. While early-stage melanomas comprised melanin-pigmented Mitf and Dct-expressing cells, expression of these and other melanocyte identity genes was lost in later stage tumours that showed histological and molecular characteristics of de-differentiated neural crest type cells. Melanocyte identity genes displayed loss of active chromatin marks and RNA polymerase II and gain of heterochromatin marks, indicating epigenetic reprogramming during tumour progression. Nevertheless, late-stage tumour cells grown in culture re-expressed Mitf, and melanocyte markers and Mitf together with Sox10 coregulated a large number of genes essential for their growth. In this melanoma model, somatic inactivation that the catalytic Brg1 (Smarca4) subunit of the SWI/SNF complex and the scaffolding Bptf subunit of the NuRF complex delayed tumour formation and deregulated large and overlapping gene expression programs essential for normal tumour cell growth. Moreover, we show that Brg1 and Bptf coregulated many genes together with Mitf and Sox10. Together these transcription factors and chromatin remodelling complexes orchestrate essential gene expression programs in mouse melanoma cells.

Maternal thyroid function during pregnancy and puerperal period

It has been noted that hypothyroidism in pregnant women can adversely affect the children's subsequent psychoneurotic development. Also, transient elevation of serum free thyroxine is occasionally seen in the first trimester of normal pregnancy. However, normal thyroid function during pregnancy and the puerperal period has not been clearly defined in Japan. The aim of this study was to assess maternal thyroid function during pregnancy and puerperal period in Japan. The concentrations of thyroid stimulating hormone (TSH), free triiodo-thyronine (free T(3)), free thyroxine (free T(4)) and thyroid binding capacity (TBC) of 522 normal pregnant and puerperal women (119 in the first trimester; 132 in the second trimester; 135 in the third trimester and 136 in the early puerperium) were measured by electrochemiluminescence immunoassay. We compared the measured data with those of healthy nonpregnant control. Twenty-six (21.8%) of 119 women in the first trimester had lower TSH levels and 23 (16.9%) of 136 women in the early puerperium had higher TSH levels than the normal range of healthy nonpregnant controls. Free T(3) gradually decreased during pregnancy, although it remained within the normal control range. Eight (6.7%) of 119 women in the first trimester had high free T(4) levels, which gradually decreased during pregnancy. Sixty (44.4%) of 135 women in the third trimester had low free T(4) levels. The values of TBC in the second trimester increased compared with the first trimester and did not change in the third trimester and decreased after delivery. There were no correlations between maternal TSH and levels of thyroid hormones (free T(3) or free T(4)), except for TSH and free T(4) in the first trimester. In conclusion, we showed that maternal thyroid function, especially TSH and free T(4), changed during the course of pregnancy. In assessing the thyroid function associated with pregnancy, one needs to keep in mind the tendency toward low free T(4) levels in the third trimester and high TSH levels in the early puerperal period.

Management of hypo- and hyperthyroidism during pregnancy

Pregnancy has profound effects on the regulation of thyroid function, and on thyroidal functional disorders, that need to be recognized, carefully assessed and correctly managed. Relative hypothyroxinemia and goitrogenesis may occur in healthy women who reside in areas with restricted iodine intake, strongly suggesting that pregnancy constitutes a stimulatory challenge for the thyroid. Overt thyroid dysfunction occurs in 1-2% of pregnant women, but mild forms of dysfunction (both hyper- and hypothyroidism) are probably more prevalent and frequently remain unrecognized. Alterations of maternal thyroid function have important implications for fetal and neonatal development. In recent years, particular attention has been drawn to the potential risks for the developing fetus due to maternal hypothyroxinemia during early gestation. Concerning hyperthyroidism, the two main causes of thyrotoxicosis in the pregnant state are Graves' disease and gestational transient thyrotoxicosis (GTT). The natural history of Graves' disease is altered during pregnancy, with a tendency for exacerbation during the first trimester, and amelioration during the second and third trimesters. The natural history of the disorder must be considered when treating patients, since antithyroid drugs cross the placenta and can directly affect fetal thyroid function. Algorithms to routinely screen pregnant women for thyroid dysfunction have been proposed in recent years, but these have not yet been implemented systematically, nor have they been the subject of cost-effectiveness analyses.

The systematic screening and management of hypothyroidism and hyperthyroidism during pregnancy

Altogether, thyroid function abnormalities during pregnancy can affect up to 10% of all women. The high prevalence of both hypo- and hyperthyroidism, the obstetrical repercussions associated with thyroid dysfunction in the mothers, as well as the potential role of maternal thyroid dysfunction as an influence on fetal development constitute solid arguments for a further increase of our knowledge of the pathophysiological processes underlying the alterations of thyroid function related to the pregnant state. In this review, the focus will be on the most clinically relevant aspects associated with hypothyroidism [autoimmune thyroid disorders (AITDs), subfertility, risk of miscarriage, risk of hypothyroidism in women with AITD and treatment of hypothyroid women] and with hyperthyroidism (clinical presentations during pregnancy, Graves' disease and its management, fetal hyperthyroidism in women with antithyroid-stimulating hormone receptor antibodies and gestational transient thyrotoxicosis associated with human chorionic gonadotropin stimulation of the maternal thyroid gland). I also propose a global strategy for the systematic screening of hypo- and hyperthyroidism in the pregnant state.

Thyroid hyperfunction during pregnancy

The present report focuses on the two main causes of hyperthyroidism observed in the pregnant state: Graves' disease (GD) and gestational transient thyrotoxicosis. Together, the prevalence of hyperthyroidism may represent 3% to 4% of all pregnancies, and therefore constitutes an important clinical issue. Concerning GD, the variable presentations of the disease (women under treatment, in remission, or considered cured) and specific alterations occurring in pregnancy are discussed: changes in thyrotropin (TSH) receptor antibody titers, the risk of fetal and neonatal thyrotoxicosis, the outcome of pregnancy in relation to the control of hyperthyroidism, and the treatment of active GD during and after pregnancy with antithyroid drugs. Gestational transient thyrotoxicosis is associated with a direct stimulation of the maternal thyroid gland by human chorionic gonadotropin (hCG), and has been shown to be directly related to both the amplitude and duration of peak hCG values. The syndrome is usually transient, observed at the end of the first trimester, and is frequently associated with emesis. Finally, we propose a global strategy for the systematic screening of hyperthyroidism during pregnancy, based on an algorithm that allows for the diagnosis of both autoimmune and nonautoimmune forms of hyperthyroidism in the pregnant state.

Maternal and perinatal outcome in thyrotoxicosis complicating pregnancy

In this report we describe 32 pregnancies complicated by hyperthyroidism cared for over a 7-year period at AIIMS, New Delhi. In 6 cases hyperthyroidism was diagnosed during pregnancy; others were diagnosed before conception and were on antithyroid therapy during pregnancy. For control of thyrotoxicosis thiourea derivatives, carbimazole (CMZ) and propylthiouracil (PTU), were both used. The dosage of antithyroid drugs could be decreased or stopped in the third trimester in only 28% cases, while 50% cases did not require any change in the dosage during gestation and 21% required an increase in dosage with advancing gestation to control thyrotoxicosis. Maternal and fetal complications included preterm labour (25%), PIH (22%), thyroid crisis (9%) and intrauterine growth retardation (13%). Thyroid status of neonates was found abnormal in 9% cases, including 1 case (3%) of neonatal thyrotoxicosis with goitre and 2 (6%) cases of neonatal hypothyroidism. One maternal death occurred due to thyroid storm. No case of stillbirth or perinatal death occurred in the present study. In our experience of 32 cases maternal and fetal complications are reported with increased frequency, requiring close surveillance of thyroid status to maintain euthyroidism and intensive fetal monitoring during pregnancy to achieve good maternal and perinatal outcome.

Thyroid disease and pregnancy

Thyroid disease is common in younger women and may be a factor in reproductive dysfunction. This probably only applies to severe cases of hyper- or hypothyroidism. Once adequately treated, neither of these disorders significantly impacts on fertility. The key is to recognize and to treat thyroid disorders in the reproductive-age woman before conception. Thyroxine therapy and even antithyroid drug therapy should be continued during pregnancy as necessary. Pregnancy is a euthyroid state that is normally maintained by complex changes in thyroid physiology. The fetal and neonatal hypothalamic-pituitary-thyroid system develops independently, but it may be influenced by thyroid disease in the mother. Early pregnancy is characterized by an increase in maternal T4 secretion stimulated by hCG and an increase in TBG, resulting in the elevated total serum T4 in pregnancy. The debate continues as to whether maternal T4 is important in early or late fetal brain development. If so, the physiologic changes in thyroid hormone secretion and transport in early pregnancy would help to ensure that a sufficient amount of thyroid hormone was available. There is new evidence in human subjects that substantial maternal T4 can cross the placenta during pregnancy, and this may be particularly important when fetal thyroid function is compromised as a result of congenital hypothyroidism. Maternal and fetal/neonatal outcomes in pregnancy are adversely affected if severe hypothyroidism is undiagnosed or inadequately treated. Thyroid function tests should be obtained during gestation in women taking T4 and appropriate dose adjustments should be made for TSH levels outside a normal range. The TSH-receptor blocking antibodies from the mother are a recognized cause of congenital hypothyroidism in the fetus and neonate that can be permanent or transient. If neonatal hypothyroidism is detected through neonatal screening programs, and prompt and adequate T4 replacement therapy is instituted as soon as possible following delivery, subsequent growth and development are usually normal. Paradoxically, pregnancy often has a favorable effect on the course of maternal Hashimoto's disease, although there is the risk of relapse postpartum. Pathophysiologic conditions of hCG secretion such as gestational trophoblastic disease and hyperemesis gravidarum may present as thyrotoxicosis in pregnancy, but the main cause of this syndrome is Graves' disease. The mainstay of treatment is antithyroid drugs and either propylthiouracil or methimazole may be used safely. Subtotal thyroidectomy, after medical control, is the alternative treatment, but radioiodine ablation is contraindicated.(ABSTRACT TRUNCATED AT 400 WORDS)