||To date, more than 1500 sequence variants have been reported to the CF mutation database. These include point mutations, deletions, insertions, frameshift mutations and splice-site variants that lead to protein truncation. The incidence of CF (approximately 1/3000 individuals) is highest in Caucasians and Ashkenazi Jews, which are the most extensively studied populations. In other ethnic backgrounds, the incidence is lower and knowledge of mutation spectra is still somewhat limited. It is clear, however, that the range and frequency of individual CFTR mutations varies considerably among different populations, ethnic backgrounds, and geographic locations. A limited number of exonic rearrangements of CFTR have been identified, suggesting that exon deletions and duplications are of clinical importance in the etiology of CF, albeit in a minority of cases. The overall frequency of large rearrangements is probably underestimated due to the testing methods commonly used, but is likely to account for several percent of all affected alleles.
Patients for whom a second CF mutation is not detected by whole gene sequencing may be further tested, when clinically indicated, with the MLPA assay (multiplex ligation-dependent probe amplification), to detect large deletions or duplications in the CFTR gene. Copy number changes of one or more exons will account for less than 10% of all CFTR mutations in most populations.