Mild CF phenotype associated with T3381 missense mutation

A Genotypic-Oriented View of CFTR Genetics Highlights Specific Mutational Patterns Underlying Clinical Macrocategories of Cystic Fibrosis

Cystic fibrosis (CF) is a monogenic disease caused by mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The genotype-phenotype relationship in this disease is still unclear, and diagnostic, prognostic and therapeutic challenges persist. We enrolled 610 patients with different forms of CF and studied them from a clinical, biochemical, microbiological and genetic point of view. Overall, there were 125 different mutated alleles (11 with novel mutations and 10 with complex mutations) and 225 genotypes. A strong correlation between mutational patterns at the genotypic level and phenotypic macrocategories emerged. This specificity appears to largely depend on rare and individual mutations, as well as on the varying prevalence of common alleles in different clinical macrocategories. However, 19 genotypes appeared to underlie different clinical forms of the disease. The dissection of the pathway from the CFTR mutated genotype to the clinical phenotype allowed to identify at least two components of the variability usually found in the genotype-phenotype relationship. One component seems to depend on the genetic variation of CFTR, the other component on the cumulative effect of variations in other genes and cellular pathways independent from CFTR. The experimental dissection of the overall biological CFTR pathway appears to be a powerful approach for a better comprehension of the genotype-phenotype relationship. However, a change from an allele-oriented to a genotypic-oriented view of CFTR genetics is mandatory, as well as a better assessment of sources of variability within the CFTR pathway.

Mild cystic fibrosis mutations in Southern Sweden with special reference to S549I and T338I

In this study of cystic fibrosis (CF) gene mutations in Southern Sweden we found missense mutations in 12 out of 110 patients. These patients, as a group, differed from deltaF508 homozygotes by a higher frequency of pancreatic sufficiency and an older age at diagnosis as has been indicated in previous studies. In addition, lung function (vital capacity (VC) and forced expiratory volume in 1 s (FEV1)) tended to be better although the difference did not reach statistical significance (p = 0.13 for FEV1). For two mutations, S549I and T338I, our results differed from earlier reports. In our experience, S549I confers a milder phenotype and T338I a more severe one than previously reported. We conclude that each mutation should be treated separately when trying to correlate genotype with phenotype.