Point mutations of the alpha-subunit of the
stimulatory G protein (Gs alpha) (termed gsp) and the
TSH receptor, leading to constitutive elevation of intracellular cAMP contents, have recently been described in autonomously functioning
thyroid adenomas. Since we have recently found a clear difference in the incidence of such gain-of-function mutations of the
TSH receptor between Japan and Europe, the present study was designed to evaluate the incidence of gsp mutations in a series of autonomously functioning
thyroid adenomas in a Japanese population. Thirty-eight autonomously functioning
thyroid adenomas were employed in the present study. Genomic
DNA was extracted from archival
formalin-fixed,
paraffin-embedded tissue specimens. Exons 8 and 9 of the Gs alpha gene were examined for activating mutations at
codons 201 and 227 by single-strand conformation polymorphism (SSCP) and
nucleotide sequencing. Both exons 8 and 9 were successfully amplified in 28 of 38 samples by polymerase chain reaction. Of these only one sample for exon 9 displayed a distinct migration pattern in SSCP analysis, in which a point mutation of a G to C transversion was identified by
nucleotide sequencing, resulting in substitution of His (CAC) for Gln (CAG) at
codon 227. The wild-type sequence of exon 9 in 10 randomly selected samples with an identical migration pattern in SSCP analysis suggests that underestimation of the incidence of gsp mutations is unlikely in our work. In conclusion, the present data, together with our previous data on the
TSH receptor, suggest that oncogenic mutations of the Gs alpha as well as the
TSH receptor do not seem to play a major role in
tumorigenesis of autonomously functioning
thyroid adenomas in Japan.