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Journal of Thyroid Research
Volume 2010, Article ID 703978, 5 pages
http://dx.doi.org/10.4061/2010/703978
Case Report

TSH Isoforms: About a Case of Hypothyroidism in a Down's Syndrome Young Adult

1Laboratoire du Service de Médecine Nucléaire, Centre Hospitalier de Chambéry, 73000 Chambéry, France
2Département de Biologie Intégrée, Centre Hospitalier et Universitaire de Grenoble, F38043 Grenoble Cedex 9, France
3Société Française de Médecine Nucléaire, Groupe de Biologie Spécialisée, Centre Antoine Béclère, 45 rue des Saints Pères, 75270 Paris, France
4INSERM U877, 38000 Grenoble, France
5Neurodiag, UMR 6149, CNRS et Université de Provence, 13331 Marseille, France
6Unité Fonctionnelle Endocrinologie, Nutrition, Métabolisme, Département de Biologie, Hospices Civils de Lyon, Centre Hospitalier Lyon sud, 69495 Pierre-Bénite, France
7INSERM U590, Lyon 69008, France
8Service Endocrinologie, Diabète, Nutrition, Hospices Civils de Lyon, Centre Hospitalier Lyon Sud, 69495 Pierre-Bénite, France
9Department of Endocrinology, The Christie, Manchester M20 4BX, UK
10Faculté de Médecine Lyon Sud-Charles Mérieux, Université de Lyon, 69622 Lyon, France

Received 4 March 2010; Revised 11 June 2010; Accepted 17 June 2010

Academic Editor: Paolo Beck-Peccoz

Copyright © 2010 Anne-Sophie Gauchez et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background. For unknown reasons, the prevalence of thyroid autoimmune disorders is higher in patients with Down's syndrome than in the general population. The present case strongly supports a recent evaluation of propagating screening for thyroid disease in this group of patients to assure early diagnosis of hypothyroidism. Methods. In a 25-year-old man diagnosed with Down's syndrome, clinical manifestations of hypothyroidism were lacking, but profound biochemical abnormalities were found with particularly high levels of thyroid stimulating hormone (TSH). Antigenic properties of TSH were characterized using a panel of anti-TSH antibodies. Results. Technical problems not infrequently associated with TSH measurements are convincingly ruled out. Antigenic characterization of the patient's circulating TSH revealed circulating forms of TSH different from pituitary TSH which closely resembled TSH recombinant human hormone. Conclusions. It appears counterintuitive that the bioactivity of TSH decreases in the hypothyroid state as higher bioactivity of TSH is anticipated in hypothyroidism promoted by an increased hypothalamic TRH drive. In contrast, diminished negative thyroid hormone feedback will enhance posttranslational glycosylation of TSH subunits and increase sialylation of the carbohydrate side chains. Both exert a negative effect on TSH bioactivity, only compensated by the very high levels of the hormone as in the present case.