AB174. Genetic counseling in the couple with compound heterozygous carrier based on the result of mutation effect analysis on cystic fibrosis transmembrane conductance regulator (CFTR) protein

Background: Cystic fibrosis (CF) is an autosomal recessive disorder due to mutation(s) in the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene. In Caucasian population, CF is routinely screened in the newborns and also couple with CF family history due the high incidence and prevalence. The V322A missense mutation was detected from a man whose expecting spouse is carrier for F508del. F508del is known as the most common severe CF-causing mutation, while the effect of V322A mutation is still unknown. If V322A is deleterious, the F508del/V322A baby will suffer from CF, thus prenatal diagnosis is necessary. To evaluate the impact of V322A mutation to CFTR protein in silico and in vitro and to provide proper genetic counselling to the couple with compound heterozygous carrier.

Methods: In silico and in vitro studies of the impact of V322A mutation on CFTR protein were conducted. The mutation effect was predicted by two in silico studies: PolyPhen-2 and SWISS-MODEL Workspace. Following the in silico studies, biological studies were performed to analyze the impact of V322A mutation on protein maturation and localization. The risk of having affected offspring if she/he carries both mutations (F508del-V322A) in the gene was estimated by using Bayesian calculation.

Results: PolyPhen-2 revealed that V322A mutation is predicted to be possibly damaging, while SWISS-MODEL Workspace showed that the mutation does not have deleterious effect to the structure of protein. Western blot results showed that V322A protein has the same maturation degree with the wild type. Protein localization by immunofluorescence revealed that V322A does not alter the CFTR trafficking process. Bayesian calculation predicted that the couple has low risk to having a CF baby.

Conclusions: V322A substitution is likely a normal CFTR variant though in silico tools showed different predictions. Since the risk of having CF baby is low, therefore prenatal diagnosis is conducted only if the parents consent to it.

Keywords: Cystic fibrosis transmembrane conductance regulator (CFTR); cystic fibrosis; genetic counselling