TSHR and hyperthyroidism: However, prolonged exposure (>2 months) to high-iodine diet led to the development of colloid goiter with large follicles and a thin thyroid epithelium in the homozygous TSHR M453T mice, whereas, under sufficient-iodine diet, their thyroid histology showed features seen typically in hyperthyroidism and high TSH stimulation (hyperplasia, protrusion, reduced amount of colloid).