Etiology The cause may be sporadic or familial, goitrous or nongoitrous Defective embryogenesis 75 genesIs, dysgenesIs, ectopia Dyshormonogenesis Pit-1, TSH, TSHR, TTF-L TTF-IL, Pax 8, TG, tPO defect, etc. lodide transport defect, organification defect coupling defect, iodotyrosine deiodinase defect, ina bility of tissuses to convert t4 to T3 Deficiency or excess of iodineEtiology • The cause may be sporadic or familial, goitrous or nongoitrous • Defective embryogenesis 75% Agenesis, dysgenesis, ectopia • Dyshormonogenesis Pit-1, TSH, TSHR, TTF-I, TTF-II, Pax 8, TG, TPO defect, etc. Iodide transport defect, organification defect, coupling defect, iodothyrosine deiodinase defect, inability of tissueses to convert T4 to T3 • Deficiency or excess of iodine