Proteinuria in cystic fibrosis: a possible correlation between genotype and renal phenotype

Objective: To assess proteinuria in patients with cystic fibrosis (CF), and to correlate proteinuria with genotype, CF-related diabetes and disease severity. Methods: A prospective study was carried out over a six-month Period and involving 22 CF patients. After the collection and analysis of 24-h urine samples, the patients were divided into two subgroups: protein excretion < 150 mg/day (low-proteinuria); and protein excretion 150 mg/day (high-proteinuria). Patient charts were reviewed to obtain data on genotype and CF-related diabetes. Disease severity was assessed based on acute exacerbations in the last six months and FEV1 measured during the study period. To assess the correlation between genotype and proteinuria, the two main mutations (Delta F508 and R334W) were evaluated. Due to the existence of genotype Delta F508/R334W, two categories were created to enable statistical analysis, Delta F508 being evaluated in category 1 and R334W being evaluated in category 2. Results: The Delta F508 mutation tended to be associated with normal protein excretion: 100% of the low-proteinuria subgroup patients were considered Delta F508 in category 1, compared with 86.7% in category 2. Protein excretion tended to be higher in patients with the R334W mutation: 60.0% of the high-proteinuria subgroup patients were considered R334W in category 1, compared with 80.0% in category 2 (p = 0.009 and p = 0.014, respectively). No significant association was found for any of the other variables. Conclusions: The results suggest that genotype is associated with renal phenotype, depending on the mechanism by which the genotype alters the function or the cystic fibrosis transmembrane conductance regulator gene.