The thyroid stimulating hormone receptor (TSHR) is expressed in the membrane of thyroid follicular cells. It is involved in regulating thyrocyte cell growth and function. TSHR is also the target autoantigen in thyroid autoimmune diseases. Autoantibodies to TSHR that act as agonists are responsible for the hyperthyroidism of Graves" Disease. Another class of autoantibodies that block the binding of TSH to TSHR may mediate the hypothyroidism associated with Hashimoto"s thyroiditis, primary myxoedema, and neonatal hypothyroidism. This TSHR cell line contains the cDNA sequence identical to GenBank sequence NM_000369 except for one base pair mutation that results in a change in amino acid at position 727 (from glutamic acid to aspartic acid). This has been reported as a natural variant. The allele with glutamic acid has been proposed as a predisposing factor in toxic multinodular goiter pathogenesis.