Autosomal Dominant Polycystic Kidney Disease via the PKD2 Gene

Autosomal dominant polycystic kidney disease (ADPKD) is a common inherited kidney disease with multisystem involvement. ADPKD is characterized by bilateral renal cysts accompanied by cysts in other organs including the liver, seminal vesicles, pancreas, and arachnoid membrane (Harris et al. 2011. PubMed ID: 20301424). Renal symptoms include hypertension, renal pain, and renal insufficiency. Nearly half of ADPKD patients have end-stage renal disease (ESRD) by age 60 years. The progressive growth of liver cysts is the most common extrarenal manifestation of ADPKD. The most important non-cystic manifestations of ADPKD are vascular and cardiac abnormalities including intracranial aneurysms, mitral valve prolapse, dilatation of the aortic root, dissection of the thoracic aorta, and abdominal wall hernias. The clinical spectrum of ADPKD is wide and substantial variability of disease severity can occur even within the same family.

PKD1 and PKD2 are the two major causative genes for ADPKD (Rossetti et al. 2007. PubMed ID: 17582161; Audrézet et al. 2012. PubMed ID: 22508176). Accounting for a small fraction of ADPKD cases, GANAB and DNAJB11 are newly implicated in ADPKD (Porath et al. 2016. PubMed ID: 27259053; Cornec-Le Gall et al. 2018. PubMed ID: 29706351).

PKD2 (15 coding exons) encodes a member of the polycystin protein family. This protein together with the protein encoded by PKD1, plays an important role in renal tubular development. Genetic defects of PKD2 account for approximately 15% of genetically positive ADPKD and have been found across the whole coding region of the gene (Rossetti et al. 2007. PubMed ID: 17582161; Audrézet et al. 2012. PubMed ID: 22508176). Truncating changes (nonsense, typical splicing variants and frame-shifting small deletion/insertions) are the vast majority of PKD2 defects while relatively fewer pathogenic missense variants and small in-frame changes in PKD2 have been observed (Rossetti et al. 2007. PubMed ID: 17582161; Audrézet et al. 2012. PubMed ID: 22508176). Large deletions and duplications have also been reported, but are rare (<4%) (Bataille et al. 2011. PubMed ID: 22008521; Audrézet et al. 2012. PubMed ID: 22508176). The majority of PKD2 defects were found in single patients (Audrézet et al. 2012. PubMed ID: 22508176). De novo pathogenic variants account for about 10% of individuals with ADPKD in adulthood (Neumann et al. 2012. PubMed ID: 22367170).

In two large cohort studies, the overall pathogenic variants detection rate of PKD1 and PKD2 is about 89%, in which defects in PKD1 and PKD2 explain approximately 85% and 15% of genetically positive ADPKD cases, respectively (Rossetti et al. 2007. PubMed ID: 17582161; Audrézet et al. 2012. PubMed ID: 22508176). Large deletions and duplications in PKD1 and PKD2 are relatively rare (<4%) in ADPKD patients (Bataille et al. 2011. PubMed ID: 22008521; Audrézet et al. 2012. PubMed ID: 22508176).

This test provides full coverage of all coding exons of the PKD2 gene plus 10 bases of flanking noncoding DNA in all available transcripts along with other non-coding regions in which pathogenic variants have been identified at PreventionGenetics or reported elsewhere. We define full coverage as >20X NGS reads or Sanger sequencing. PGnome panels typically provide slightly increased coverage over the PGxome equivalent. PGnome sequencing panels have the added benefit of additional analysis and reporting of deep intronic regions (where applicable).

Dependent on the sequencing backbone selected for this testing, discounted reflex testing to any other similar backbone-based test is available (i.e., PGxome panel to whole PGxome; PGnome panel to whole PGnome).