Since the discovery and characterization of the CFTR gene, more than 100 sequence polymorphisms have been identified in this gene [1].

Some of these are located in the coding region (exon polymorphisms), while some are in the non-coding regions of the CFTR gene (intron polymorphisms). Polymorphisms located within exons are usually substitutions of 1 base pair (bp) that cause no change in amino acid sequence, or less frequently, cause the change of an amino acid with a similar one. Intron polymorphisms are also predominantly 1 bp pair substitutions.

Although most CFTR polymorphisms do not affect the function of CFTR protein, some do affect CFTR gene expression. For example, the Tn polymorphism in intron 8 (poly T sequence) affects the level of normal CFTR mRNA, depending on the number of thymines present [2]. The presence of the 5T allele reduces the level of normal CFTR mRNA.

Routine molecular diagnostic methods are aimed at the detection of the most common mutations in the CFTR gene, but the presence of polymorphisms is not usually detected by these methods. Therefore, there is little data of polymorphism frequency in European populations, and there is no data at all for the Yugoslav population.

Polymorphism 2694T/G [1], located in exon 14a of the CFTR gene, causes no change in amino acid sequence of the CFTR protein (Thr at 854), but the possibility that it might affect gene expression is not excluded [3]. One of the ways to come to some conclusions about the consequences of CFTR polymorphism presence can be made from genotype-phenotype studies.