Thyroid Physiology Studies of Inherited Disorders

The broad objective of this research proposal is to advance our understanding of thyroid physiology through the study of genetic defects at key regulatory processes. In addition to identification of new syndromes and gene defects, research centers on regulation of gene expression and gene therapy. The program owes its success to the worldwide referral of patient material, to the clinical and technical skills of the PI’s laboratory, and to collaborative arrangements with accomplished investigators from the US and abroad that provide complementary knowledge and technical expertise. The proposal by multiple PIs for continuing funding encompasses three aims. (1) Determine the mechanism by which several newly identified genetic defects produce the observed thyroid phenotypes. These include the selenoenzyme deiodinases D1 and D3; PKHD1L1 mutations by studying the Pkdh1l1KO mice; and LRP2 mutations by in vitro structural and functional characterization. (2) Determine the mechanism of resistance to TSH (RTSH) caused by mutations in a primate- specific short tandem repeat (STR) on chromosome-15. Human thyroid organoids recently developed in collaboration will be used to generate STR mutant thyroid organoids using CRISPR/Cas9 or PiggyBac transposon as a genome editing tool, in order to study the physiological function of this primate specific STR and its role in the dominantly inherited phenotype of RTSH. TSH sensitivity of normal and mutant organoids will be determined in vitro or in vivo after transplantation into hypothyroid mice. (3) Determine the effectiveness of combined gene and thyroid hormone (TH) analogue treatments in monocarboxylate 8 (MCT8) deficiency. The X chromosome linked MCT8 deficiency produces in boys a disease known as Allan-Herndon-Dudley-Syndrome (AHDS) with severe neuropsychomotor defects, caused by deficiency of TH transport in brain, and systemic thyrotoxicosis caused by excess of circulating T3. Double knockout (dKO) mice, lacking Mct8 and the TH transporter Oatp1c1, recapitulate the findings of AHDS. We recently showed that gene therapy in peripubertal dKO mice with adeno associated virus 9 (AAV9) containing the human MCT8 cDNA improved the locomotor and cognitive function by near normalization of brain T3 content but failed to correct the serum thyroid tests. We propose to add the TH analogues diiodothyropropionic acid (DITPA) or triiodothyroacetic acid (TRIAC) that are known to correct the thyrotoxicosis of AHDS in peripheral tissues but not the neuropsychomotor manifestations, to achieve rescue of this incapacitating disease. The proposed research will result in the discovery of new genes and mechanisms causing congenital and inherited thyroid diseases. In addition to knowledge gained regarding thyroid physiology and pathophysiology, these studies will provide the means for rapid and specific diagnosis and for rationale of innovative treatments.