Identification of an 11T allele in the polypyrimidine tract of intron 8 of the CFTR gene.

Purpose: Most of the kits or reagents available for testing for mutations in the cystic fibrosis transmembrane conductance regulator gene include testing for the 5/7/9T polypyrimidine tract, but these methods only screen for three variants in this region: 5T, 7T, and 9T. Although such commercial products may not have been designed to screen for rare alleles of the polypyrimidine tract, we demonstrate that at least one of them (Tag-It Cystic Fibrosis Kit, Tm Bioscience, Toronto, Ontario, Canada) has enough sensitivity to differentiate samples with rare alleles by describing how this product allowed us to detect a previously uncharacterized 11T allele.

Methods: A total of 139 banked and anonymized clinical samples from carrier adults and children with cystic fibrosis (The Hospital for Sick Children, Toronto, Canada) were tested and analyzed using the Tag-It Cystic Fibrosis Kit.

Results: Two samples displayed allelic ratios for the polypyrimidine tract that were significantly different from the other samples and did not correspond to values expected to be seen for samples with 5T, 7T, or 9T alleles. Further tests with sequencing and an extended Tag-It assay confirmed the presence of an 11T allele.

Conclusion: Although commercial products used in cystic fibrosis testing may not have been designed to screen for rare alleles of the polypyrimidine tract, we demonstrated that at least the Tag-It assay may have enough sensitivity to differentiate samples with such rare alleles, which can then be further analyzed for clarification.