Polymorphism of a variant human thyrotropin receptor (hTSHR) gene

Sequencing of the human thyrotropin receptor (hTSHR) gene using genomic DNA from peripheral blood leukocytes revealed a substitution of nucleotide 253 in the cDNA sequence. The replacement of the wild-type cytosine-253 to adenine results in the replacement of the wild-type Pro at codon 52 (CCC) with Thr (ACC) located in exon 1 of the TSHR. We screened genomic DNAs from 60 unrelated individuals for the presence of A253 by PCR amplification using a degenerate oligonucleotide primer that produces a Tth111 I restriction site only in the presence of A253. We found 12% having heterozygosity and all had normal free thyroxine index (FT4I) and TSH levels. We have no information concerning the functional significance of this amino acid substitution. However, in the heterozygous state, the variant allele does not result in thyroid function abnormalities.