Structure and characterization of a 50 bp repeat in intron 10 of the human thyroid peroxidase gene.

We have previously identified an EcoRI polymorphism detected by a human thyroid peroxidase (hTPO) cDNA probe, with alleles varying in size from 3.0 to 4.1 kb. For further characterization of this polymorphism, we have cloned the genomic region containing this polymorphism. Sequence analysis of a 3.2 kb EcoRI fragment containing the polymorphism revealed nine copies of a 50 bp direct repeat located 1.9 kb downstream of exon 10. In 50 unrelated Caucasian individuals, the number of repeats was determined and varied from 9 to 31, with an average of 21. Since exon 10 has been shown to be alternatively spliced in hTPO mRNA, we have also tested whether the number of 50 bp repeats affects alternative splicing of exon 10. We find no correlation between the number of repeats in intron 10 and the ratio of alternatively spliced hTPO-1 and hTPO-2 mRNA in six human thyroid glands.