Relationship between CFTR and CTRC variants and the clinical phenotype in late-onset cystic fibrosis disease with chronic pancreatitis

Cystic fibrosis (CF), the most common autosomal recessive disease in whites, is caused by mutations in the CF transmembrane conductance regulator (CFTR). So far, >1900 mutations have been described, most of which are nonsense, missense, and frameshift, and can lead to severe phenotypes, reducing the level of function of the CFTR protein. Synonymous variations are usually considered silent without pathogenic effects. However, synonymous mutations exhibiting exon skipping as a consequence of aberrant splicing of pre-mRNA differ. Herein, we describe the effect of the aberrant splicing of the c.273G>C (G91G) synonymous variation found in a 9-year-old white (ΔF508) patient affected by CF and pancreatitis associated with a variant in chymotrypsin C (CTRC). Magnetic resonance imaging showed an atrophic pancreatic gland with substitution of the pancreatic parenchyma with three cysts. Genetic examination revealed compound heterozygosity for the c.1521_1523delCTT (ΔF508) pathogenic variant and the c.273G>C (G91G) variant in CFTR. Sweat test results confirmed the diagnosis of CF. We have thus identified a synonymous variation (G91G) causing the skipping of exon 3 in a CF patient carrying the ΔF508 mutation. However, the clinical phenotype with pancreatic symptoms encouraged us to investigate a panel of pancreas-related genes, which resulted in finding a known sequence variation inside CTRC. We further discuss the role of these variants and their possible interactions in determining the current phenotype.