Over the last years, reports of familial cases with multipleaffected members, and studies on molecular biology have demonstrated the involvement ofgenes (TTF1 and 2, PAX8, TSH-R) which codify highly conserved transcription factorswhich, if inactivated, result in thyroid agenesis, ectopia and hypoplasia. This evidence concerns the gene TTF1 and hypothyroidism, congenital, nongoitrous, 2.