Characterization of a recurrent 3.8kb deletion involving exons 17a and 17b within the CFTR gene

Large deletions within CFTR have been estimated to constitute 1-2% pathogenic alleles, but the occurrence could be much higher in classical cystic fibrosis (CF) patients with one mutation detectable by the routine screening/sequencing work-up. Currently, evaluation of major CFTR rearrangements is not included in the mutation analysis for the reproductive partner of a CF patient/carrier.

Exon sequencing and Multiplex Ligation-dependent Amplification (MLPA) analyses were used to make a molecular diagnosis of two unrelated CF patients. Long PCR, restriction mapping, cloning, and hot start sequencing were employed to accurately annotate the rearrangement junctions.

Both patients had a heterozygous single amino acid deletion mutation identified by sequencing, and a heterozygous deletion of CFTR exons 17a and 17b detected by MLPA. Molecular characterization of the rearrangement breakpoints indicated that the two patients had an identical complex c.2988+1616_c.3367+356del3796ins62 change, flanked by a pair of perfectly inverted repeats of 32 nucleotides.

The c.2988+1616_c.3367+356del3796ins62 complex rearrangement is a recurrent mutation from patients of different ethnic backgrounds. This mutation can be detected through a simple PCR based analysis.