Detection of a rare-cutter RFLP in a CpG-rich island near the cystic fibrosis locus

The probe pCS. 7, isolated from an HpaII tiny fragments (HTF) island and tightly linked to the mutation causing cystic fibrosis (CF), detects a polymorphism with the rare-cutter restriction enzyme BssHII. In a single digest, the resulting restriction fragment length polymorphism (RFLP) cannot be detected by either conventional or pulse-field gel electrophoresis. A double digest with BssHII in conjunction with a six-cutter restriction enzyme that does not recognize a site containing a CpG dinucleotide enables the probe to be used routinely for prenatal diagnosis and carrier exclusion. This strategy can be used to identify polymorphisms in HTF islands.