Thyroid dysgenesis: screening and functional analyses of mutations of the candidate-genes NKX2.5, HAND2, ISL1, TBX1, HOXA3/HOXB3/HOXD3 and EYA1 in a cohort of 601 patients with congenital hypothyroidism

Abstract

Congenital hypothyroidism (CH) is the most common disorder of the endocrine system among newborns. The global incidence of CH is 1/3000-4000 births [1]. CH is mainly caused by developmental defects on thyroid, collectively known as thyroid dysgenesis (TDs). It is believed that the major causes of TDs result from impaired specification, proliferation or survival of thyroid precursor cells, while there is a loss of organized movement of these cells in a distinct spatiotemporal pattern. Thyroid development is under control of a combined expression of a set of transcription factors such as: Nkx2.1, Foxe1, Pax8 and Hhex.In a previous TD project, we had searched for mutations in these genes-related to embryogenesis of the thyroid gland Nkx2-1, Pax8, Foxe1, Nkx2-5, besides TSH receptor, TSHr, from the former cohort of children from "Programa de Rastreamento do Hipotirodismo Congenito do Estado do Paraná" (FAPESP 2006/54950-6). We have demonstrated that the prevalence of permanent CH is 1:4795, and the ectopic thyroid gland is the most frequent CH cause (37%), followed by dyshormonogenesis (28%), agenesis (24%), hypoplasia (10%) and hemiagenesis (1%). In the molecular analysis, we have identified mutations already reported in PAX8 and TSH-r genes, and new mutations in NKX2.5 gene [57].Since this study, new genes have been described on thyroid gland development; some of them already studied in animal models, and related to a possible DT pathogenesis, such as HAND2, ISL1, TBX1, HOXA3, HOXB3, HOXD3, EYA1 and HHEX. So, the aim of this project is to expand the panel of candidate-genes responsible for DTs in the same cohort of children, however, including new cases from two other Thyroid Ambulatories (Adult and Pediatric Endocrinology) of EPM/UNIFESP with hypoplasia and hemiagenesis. Thereafter, we will proceed with mutation screening in these new genes related to thyroid gland embryogenesis and its functional analyses, when a mutation is present. We will go on initially with the functional analyses of mutations already found in NKX2.5 transcription factor. In a second step, we will perform the whole exome sequencing to identify new mutations in other genes initially not related to TDs in animal models. (AU)