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


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.
Dedoussis
G V Z
GV
Department of Science Dietetics-Nutrition, Harokopio University of Athens, Athens, Greece. dedousi@hua.gr
Luo
Y
Y
Starremans
P
P
Rossetti
S
S
Ramos
A J
AJ
Cantiello
H F
HF
Katsareli
E
E
Ziroyannis
P
P
Lamnissou
K
K
Harris
P C
PC
Zhou
J
J
D000818:Animals; D002478:Cells, Cultured; D004252:DNA Mutational Analysis; D004586:Electrophoresis / Q000379:methods; D005260:Female; D006720:Homozygote; D006801:Humans; D008297:Male; D051379:Mice; D009154:Mutation; D016891:Polycystic Kidney, Autosomal Dominant / Q000235:genetics*; D016133:Polymerase Chain Reaction; D011506:Proteins / Q000235:genetics*; D050396:TRPP Cation Channels
D011506:Proteins; D050396:TRPP Cation Channels