Diagnostic usefulness of the polymorphism of the GT dinucleotide and the polythymidine tract in intron 8 of the cystic fibrosis transmembrane conductance regulator (CFTR) gene.

15-20% of the CF mutation are expected to be rare and escape detection by systems designed to screen for common mutations. The highly polymorphic simple repeats would be particularly useful for genetic diagnosis in CF families where the mutations have not been identified. In this study, we used denaturing gradient gel electrophoresis with psoralen-modified oligonucleotide primers to study the GTnTm polymorphism previously identified at the intron 8 - exon 9 junction of the CFTR gene. Twelve characteristic patterns were identified. The most frequent genotype in CF alleles was GT10T9 and in non-CF alleles GT11T7. In this study, the heterozygous incidence is 70% in unrelated CF carriers. This polymorphism is full informative in 45% and half-informative in 50%. We conclude, that this polymorphism, easy to study by a relatively simple, rapid and cheap procedure, would be particularly useful in genetic counselling for CF and prenatal diagnosis in CF families in which mutations have not been yet identified.