[Point mutations of the thyrotropin receptor gene in autonomously functioning thyroid gland nodules: correlation with...

Seventeen autonomously functioning thyroid nodules (AFTN) were analyzed for the most frequent mutations of the thyrotropin (TSH) receptor gene at codons 619, 631, 632 and 633. DNA was extracted from formalin-fixed, paraffin-embedded samples from both nodules and surrounding tissue after micro- or macrodissection. A fragment of the TSH receptor gene (bp 1762-1976) encoding the third cytoplasmic loop and the sixth transmembranous domain was amplified by PCR. Screening for mutations at codons 619, 631, 632 and 633 was performed by restriction enzyme analysis using Asp 718, Hph I, Taq I and EcoR I, respectively. For verification, cases with a mutated restriction site were cloned and sequenced. Mutations were found in 3 AFTNs (18%): in 2 cases at codon 632 and in 1 case at codon 631. The 2 cases with a mutation at codon 632 harbored additional mutations at codon 599 and 640, respectively, detected by sequencing. Normal thyroid tissue outside the AFTNs did not harbor mutant TSH-receptor. Mutations occurred in patients with clinical and subclinical hyperthyroidism. Mutations were associated both with total (2 cases) and partial (1 case) suppression of the surrounding thyroid tissue as noted on the scinti scan. AFTNs with TSH-receptor mutation occurred as single nodules. All 3 nodules with mutations were classified histologically as nodular hyperplasia according to the criteria of the WHO. Although the number of cases is small, our data suggest that AFTNs are clinically and morphologically heterogenous. Since the most common TSH-receptor mutations occur only in a small subset of AFTNs other molecular genetic alterations may be involved in the development of AFTNs.