Location of mutations within the PKD2 gene influences clinical outcome

Background. Since the cloning of the gene for autosomal dominant polwycystic kidney disease type 2 (PKD2), approximately 40 different mutations of that gene have been reported to he associated with the disease. The relationship between the PKD2 genotype and phenotype. however, remains unclear. Methods. Detailed clinical information was collected for PKD2 families in which the underlying mutation had been identified. Logistic regression analysis was employed to assess the influence of age and sex on hypertension. hematuria. renal calculi. and urinary tract infections, and a clinical phenotype score was computed. Patients were then grouped according to the relative location of their mutation within the cDNA sequence, and differences in the mean phenotypic score between groups were tested for statistical significance by means of a multiple pairwise t-test. Results. While phenotypic scores for each mutational group revealed a considerable degree of intragroup variability, the variability in phenotypic scores was significantly higher between mutational groups than within groups. A group-wise comparison of the mean phenotypic scores confirmed the observation of significant nonlinear variation in disease severity, with high- and low-scoring mutational groups interspersed along the gene sequence. Conclusion. The identification of groups of mutations in the PKD2 gene, which differ significantly with respect to clinical outcome, is to our knowledge the first description of a genotype/phenotype correlation in autosomal dominant polycystic kidney disease. It also provides evidence against complete loss of f'unction of the mutant PKD2 gene product.