China
Africa
Explore chapters and articles related to this topic
Inherited Abnormalities in Thyroid Hormone Transport Proteins
Published in Geraldo Medeiros-Neto, John Bruton Stanbury, Inherited Disorders of the Thyroid System, 2019
Geraldo Medeiros-Neto, John Bruton Stanbury
Six types of genetic variations of TTR have been identified in association with hyperthyroxinemia or with reduced affinity for T4. Six mutant TTRs are associated with familial amyloidotic polyneuropathy and have a single nucleotide substitution at different positions of the gene.
Thyroid function
Published in Martin Andrew Crook, Clinical Biochemistry & Metabolic Medicine, 2013
Drugs causing hyperthyroxinaemia: – oestrogens raise TBG concentration, as do 5-fluorouracil, heroin and methadone,– amiodarone blocks conversion of T4 to T3, resulting in an elevation of T4 and reverse T3 concentrations,– heparin, due to fatty acid release, inhibits fT4binding to TBG,– propranolol inhibits extrathyroidal conversion of T4 to T3.
Gastrointestinal diseases and pregnancy
Published in Hung N. Winn, Frank A. Chervenak, Roberto Romero, Clinical Maternal-Fetal Medicine Online, 2021
Murtaza Arif, Anjana Sathyamurthy, Jessica Winn, Jamal A. Ibdah
In the past, HG was regarded as a dreaded complication of pregnancy. Maternal mortality was high and primarily caused by severe metabolic disturbances. Improvements in fluid and electrolyte management have dramatically reduced the mortality rate of HG to virtually zero (51). Although uncomplicated nausea and vomiting in pregnancy may be an indicator of a favorable fetal outcome (62), the effects of hyperemesis on the fetus are unclear. A study of hyperemetic pregnancies associated with abnormal thyroid function indicated a higher than expected rate of premature labor and an increased incidence of low birth weight (49). Whether these effects were due to hyperemesis or hyperthyroxinemia is unclear. Analyses of the birth weights of babies born to hyperemetic mothers have been confounded by a varied patient population. Fairweather (40) found no change in birth weight when he reviewed birth records of a large group of women with hyperemesis. However, others (62,63) have subclassified hyperemetic patients into mild versus severe disease based on maternal weight loss, heavy ketonuria, elevated urea nitrogen or creatinine, and electrolyte disturbances; those with severe hyperemesis gave birth to babies with significantly lower weights. Also more growth-retarded babies were found in the groups of mothers with hyperemesis and weight loss, or hyperemesis requiring multiple admissions (55). The risk of congenital anomalies may also be increased. One study suggested an increase in minor integumentary defects including webbed toes and an extra finger, and skin tags. However, the number of patients was small and the possible influence of anti-emetic medication was not clarified.
Free thyroxine measurement in clinical practice: how to optimize indications, analytical procedures, and interpretation criteria while waiting for global standardization
Published in Critical Reviews in Clinical Laboratory Sciences, 2023
Federica D’Aurizio, Jürgen Kratzsch, Damien Gruson, Petra Petranović Ovčariček, Luca Giovanella
Patients with genetic variants of THDP are mostly euthyroid, but because of reduced THDP-binding ability, the values of T4 or FT4 are frequently falsely elevated. This is true primarily in cases of familial dysalbuminemic hyperthyroxinemia (prevalence 0.01–1.8%, with the highest values in the Hispanic population) [260]. If this disease is suspected, the use of a physical separation method-coupled immunoassay or LC-MS/MS method to measure unbiased FT4 is necessary. TBG variants are usually associated, not with thyroid diseases, but with abnormal T4 (with TBG deficiency, T4 is low; with TBG excess, T4 is high) and normal free thyroid hormone values [261]. Mutations of TTR present an increased or decreased binding affinity for T4. While decreased TTR affinity to T4 has no effect on serum levels of thyroid hormone, increased TTR affinity leads to mildly increased T4 and normal FT4 levels if a physical separation method-coupled immunoassay or an LC-MS/MS method is used to quantify FT4 [261].
Toward a science-based testing strategy to identify maternal thyroid hormone imbalance and neurodevelopmental effects in the progeny – part I: which parameters from human studies are most relevant for toxicological assessments?
Published in Critical Reviews in Toxicology, 2020
Ursula G. Sauer, Alex Asiimwe, Philip A. Botham, Alex Charlton, Nina Hallmark, Sylvia Jacobi, Sue Marty, Stephanie Melching-Kollmuss, Joana A. Palha, Volker Strauss, Bennard van Ravenzwaay, Gerard Swaen
Hyperthyroidism (low TSH with concordant high fT4) and hyperthyroxinaemia (isolated high fT4) were excluded from the scope of this review since they are not specifically addressed in Appendix A. Nevertheless, hyperthyroidism and hyperthyroxinaemia are also relevant from a clinical perspective (Korevaar et al. 2016a; Jansen et al. 2019). Similarly, with respect to initiating events, this review considers how substance-mediated liver enzyme induction affects serum thyroid hormone levels in humans. By contrast, other important initiating events that affect serum thyroid hormone levels and, ultimately, child neurodevelopmental outcomes, such as TPO activity or iodine deficiency, are not addressed here for not being considered in Appendix A. Nonetheless, and as mentioned above, the iodine status plays a critical role in ensuring physiological thyroid function.
A practical approach towards the evaluation of aberrant thyroid function tests
Published in Acta Clinica Belgica, 2020
Barbara Vandendriessche, Bruno Lapauw, Jean Marc Kaufman, Tom Fiers
After excluding confounding drugs and analytical interference, some important pathologic causes should be considered: Patients with familial dysalbuminaemic hyperthyroxinaemia (FDH) have a dominantly inherited genetic variant of albumin with altered affinity for iodothyronines. They are clinically euthyroid as confirmed by a normal TSH, but their total T4 is elevated due to increased binding of T4. The labelled tracer used in a T4 competition assay also binds with higher affinity to albumin, leaving less tracer available for competition with non-albumin bound T4 resulting in spuriously high fT4 levels. To overcome this, equilibrium dialysis is recommended. Further, FDH can be confirmed by genetic analysis and a similar pattern of aberrant TFT is often seen in first-degree family members.