Co-inheritance of a PKD1 mutation and homozygous PKD2 variant: a potential modifier in autosomal dominant polycystic kidney disease

Authors


George Dedoussis, Assistant Professor of Biology, Department of Nutrition – Dietetics, Harokopio University, 70 El. Venizelou St., 17671 Athens, Greece. Tel.: +30-210-9549304; Fax: +30-210-9577050; E-mail: dedousi@hua.gr

ABSTRACT

Background  Autosomal dominant polycystic kidney disease (ADPKD), which is caused by mutations in polycystins 1 (PC1) and 2 (PC2), is one of the most commonly inherited renal diseases, affecting ~1 : 1000 Caucasians.

Materials and methods  We screened Greek ADPKD patients with the denaturing gradient gel electrophoresis (DGGE) assay and direct sequencing.

Results  We identified a patient homozygous for a nucleotide change c.1445T > G, resulting in a novel homozygous substitution of the non-polar hydrophobic phenylalanine to the polar hydrophilic cysteine in exon 6 at codon 482 (p.F482C) of the PKD2 gene and a de-novo PKD1 splice-site variant IVS21–2delAG. We did not find this PKD2 variant in a screen of 280 chromosomes of healthy subjects, supporting its pathogenicity. The proband's parents did not have the PKD1 mutation. Real-time PCR of the PKD2 transcript from a skin biopsy revealed 20-fold higher expression in the patient than in a healthy subject and was higher in the patient's peripheral blood mononuclear cells (PBMCs) than in those of her heterozygote daughter and a healthy subject. The greater gene expression was also supported by Western blotting. Inner medullar collecting duct (IMCD) cells transfected with the mutant PKD2 mouse gene presented a perinuclear and diffuse cytoplasmic localization compared with the wild type ER localization. Patch-clamping of PBMCs from the p.F482C homozygous and heterozygous subjects revealed lower polycystin-2 channel function than in controls.

Conclusions  We report for the first time a patient with ADPKD who is heterozygous for a de novo PKD1 variant and homozygous for a novel PKD2 mutation.

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