Additional evidence on the phenotype produced by combination of 1677delTA alleles and their relevance in causing CFTR-related disease.

Cystic fibrosis is the most common, life-threatening, autosomal recessive disease in the Caucasian population. It is caused by mutations in the cystic fibrosis transmembrane conductance regulator gene, which encodes a chloride ion channel expressed on the surface of epithelial cells. There are more than 2000 variants of the cystic fibrosis transmembrane conductance regulator gene reported worldwide.

Genotype-phenotype correlations of cystic fibrosis in siblings compound heterozygotes for rare variant combinations: Review of literature and case report.

Here, we describe a cystic fibrosis (CF) family with affected siblings, two of whom have a combination of I1234V and 1677delTA variants with classic CF features, the third child with a combination of I1234V and L997F variants with atypical CF, and the apparently healthy mother with a combination of 1677delTA and L997F alleles. Interestingly, the sibling with I1234V and L997F variants had normal sweat test results and had a much milder phenotype than the other two siblings with I1234V and 1677delTA variants, suggesting that this combination is causative for atypical CF. The fact that their mother with the combination of 1677delTA and L997F appears to be healthy suggests that the L997F variant causes different phenotypes in different allele combinations.