Background: Congenital hypothyroidism (CH) is defined as the lack of thyroid hormones at birth. Mutations in at least 15 different genes have been associated with this disease. While up to 20% of CH cases are hereditary, the majority of cases are sporadic with unknown etiology. Apart from a monogenic pattern of inheritance, multigenic mechanisms have been suggested to play a role in CH. The genetics of CH has not been studied in Finland so far. Therefore, multigenic sequencing of CH candidate genes was performed in a Finnish patient cohort with both familial and sporadic CH.Methods: A targeted next-generation sequencing (NGS) panel, covering all exons of the major CH genes, was applied for 15 patients with sporadic and 11 index cases with familial CH.Results: Among the familial cases, six pathogenic mutations were found in the TPO, PAX8, and TSHR genes. Furthermore, pathogenic NKX2.1 and TG mutations were identified from sporadic cases, together with likely pathogenic variants in the TG, NKX2.5, SLC26A4, and DUOX2 genes. All identified novel pathogenic mutations were confirmed by Sanger-sequencing and characterized in silico and/or in vitro.Conclusion: In summary, the CH panel provides an efficient, cost-effective, and multigenic screening tool for both known and novel CH gene mutations. Hence, it may be a useful method to identify accurately the genetic etiology for dyshormogenic, familial, or syndromic forms of CH.

This is the first study to reveal the dynamic age-, sex-, and genotype-dependent development of NAH. Furthermore, the study shows that a constitutively active TSHR can trigger a malignant transformation of thyrocytes.

We have created a mouse model expressing tamoxifen-inducible Cre recombinase (CreER(T2) ) under the control of the thyroglobulin (Tg) gene promoter to be able to study the role of defined genetic modifications in the regulation of thyroid function. We chose the thyroglobulin promoter, as it is expressed specifically in the thyroid. In order to obtain reliable expression under the control of the Tg promoter, we used a P1 artificial chromosome (PAC) containing a large piece of the Tg promoter. A tamoxifen inducible CreER(T2) construct was selected to avoid the possible consequences of the gene deletion for the development of the thyroid gland, and to study the role of gene deletion in the adult thyroid. Transgenic lines (TgCreER(T2) ) carrying this construct were generated and analyzed by crossing the TgCreER(T2) mice with the ROSA26LacZ reporter strain. The activity and specificity of the Cre recombinase was tested by staining for β-galactosidase activity and by immunohistochemistry using an anti-Cre-antibody. In the TgCreER(T2) xROSA26LacZ reporter line, Cre-mediated recombination occurred specifically in the thyrocytes only after tamoxifen administration, and no significant staining was observed in controls. The recombination efficiency was nearly complete, since almost all thyrocytes showed X-gal staining. We could also induce the recombination in utero by giving tamoxifen to the pregnant female. In addition, mice expressing TgCreER(T2) had no obvious histological changes, hormonal alterations, or different response to growth stimuli as compared to controls. These results demonstrate that the TgCreER(T2) mouse line is a powerful tool to study temporally controlled deletion of floxed genes in the thyroid.

Thyroid function is controlled by thyroid-stimulating hormone (TSH), which binds to its G protein-coupled receptor [thyroid-stimulating hormone receptor (TSHR)] on thyrocytes. TSHR can potentially couple to all G protein families, but it mainly activates the G- and G-mediated signaling cascades. To date, there is a knowledge gap concerning the role of the individual G protein cascades in thyroid pathophysiology. Here, we demonstrate that the thyrocyte-specific deletion of G-protein α subunit (Gα) in adult mice [tamoxifen-inducible G protein α subunit deficient (iTGαKO) mice] rapidly impairs thyrocyte function and leads to hypothyroidism. Consequently, iTGαKO mice show reduced food intake and activity. However, body weight and the amount of white adipose tissue were decreased only in male iTGαKO mice. Unexpectedly, hyperplastic follicles and papillary thyroid cancer-like tumor lesions with increased proliferation and slightly increased phospho-ERK1/2 staining were found in iTGαKO mice at an older age. These tumors developed from nonrecombined thyrocytes still expressing Gα in the presence of highly elevated serum TSH. In summary, we report that partial thyrocyte-specific Gα deletion leads to hypothyroidism but also to tumor development in thyrocytes with remaining Gα expression. Thus, these mice are a novel model to elucidate the pathophysiological consequences of hypothyroidism and TSHR/G/cAMP-mediated tumorigenesis.-Patyra, K., Jaeschke, H., Löf, C., Jännäri, M., Ruohonen, S. T., Undeutsch, H., Khalil, M., Kero, A., Poutanen, M., Toppari, J., Chen, M., Weinstein, L. S., Paschke, R., Kero, J. Partial thyrocyte-specific Gα deficiency leads to rapid-onset hypothyroidism, hyperplasia, and papillary thyroid carcinoma-like lesions in mice.

MicroRNAs (miRNAs) are important regulators of posttranscriptional gene expression and involved in embryonic development, regulation of cell differentiation, and growth. Dicer1 is a key enzyme in the maturation process of functional miRNAs. However, miRNA-mediated regulation of normal thyroid function and growth is largely unknown. To understand the role of miRNAs in the thyroid, we generated constitutive and tamoxifen-inducible, thyrocyte-specific Dicer1 knockout mice. The mice with perinatal Dicer1 deletion (cTgDcrKO) showed impaired follicular organization, increased fibrosis, and accumulation of adipocytes in the thyroid. Similar histological changes were observed in tamoxifen-induced adult Dicer1-deficient mice (iTgDcrKO). The thyroid phenotype in both knockout (KO) lines was associated with significantly down-regulated mRNA expression of thyroid transcription factor 1 (Ttf-1/Nkx2-1), thyroid peroxidase, and thyroglobulin (Tg) and up-regulated expression of genes involved in Tgf-β signaling. Furthermore, in cTgDcrKO mice, which developed mild hypothyroidism, the protein expression of Nkx2-1, thyroglobulin, Paired box 8, and TSH receptor were clearly down-regulated compared with controls. Despite similar down-regulation of Dicer1 in cTgDcrKO and iTgDcrKO compared with controls, Dicer1 deletion in adult mice thyrocytes did not lead to acute hypothyroidism. No significant differences in thyroid weights between cTgDcrKO, iTgDcrKO, and controls were observed. However, a goitrogenic diet induced a 4-fold increase in thyroid weight in control animals, whereas it had no effect on iTgDcrKO thyroids. In summary, Dicer1 deficiency in thyrocytes is associated with intrathyroid fibrosis, adipogenesis, and enhanced expression of Tgf-β signaling genes. Furthermore, our data indicate that Dicer1 is required for thyroid follicular organization, thyrocyte differentiation, and goiter development.