Autosomal Dominant Polycystic Kidney Disease: PKD2 Gene Deletion/Duplication
Test Code: 7432
Turnaround time: 3 weeks
Autosomal dominant polycystic kidney disease (ADPKD)is generally a late-onset multisystem disorder characterized by bilateral renal cysts; cysts in other organs including the liver, seminal vesicles, pancreas, and arachnoid membrane; vascular abnormalities including intracranial aneurysms, dilatation of the aortic root, and dissection of the thoracic aorta; mitral valve prolapse; and abdominal wall hernias. Renal manifestations include hypertension, renal pain, and renal insufficiency. Approximately 50% of individuals with ADPKD have end-stage renal disease (ESRD) by age 60 years.
The prevalence of liver cysts, the most common extrarenal manifestation of ADPKD, increases with age and may have been underestimated by ultrasound and CT studies. The prevalence of intracranial aneurysms is higher in those with a positive family history of aneurysms or subarachnoid hemorrhage (22%) than in those without such a family history (6%). Mitral valve prolapse, the most common valvular abnormality, occurs in up to 25% of affected individuals. Substantial variability in severity of renal disease and other extrarenal manifestations occurs even within the same family.
The diagnosis of ADPKD is established primarily by imaging studies of the kidneys. In 85% of individuals with ADPKD, mutations in the PKD1 gene are causative; in 15%, mutations in the PKD2 gene (4q21-q23) are causative. Approximately 4% of ADPKD-causing mutations are larger deletions or duplications. About 95% of individuals with ADPKD have an affected parent and about 5% have a de novo mutation. Genetic background and environmental factors account for significant intrafamilial variability in disease severity. PKD1 mutations are associated with a 20-year earlier onset of ESRD than PKD2 mutations. In PKD2, males progress to ESRD more rapidly than females; no gender difference is seen in PKD1.
ADPKD is the most common potentially lethal single-gene disorder. Its prevalence at birth is between 1:400 and 1:1,000; and it affects approximately 600,000 persons in the United States.
This testing is ONLY for the PKD2 gene.
For patients with suspected ADPKD in whom PKD1 testing is negative, sequence analysis is recommended as the first step in mutation identification. For patients in whom mutations are not identified by full gene sequencing, deletion/duplication analysis is appropriate.
This test is indicated for:
- Confirmation of a clinical diagnosis of ADPKD in patients with negative PKD1 testing who have also tested negative for sequence analysis of the PKD2 gene
- Individuals at-risk for ADPKD due to family history, in whom PKD1 testing and PKD2 sequence analysis is negative
DNA isolated from peripheral blood is hybridized to a CGH array to detect deletions and duplications. The targeted CGH array has overlapping probes which cover the entire genomic region.
Please note that a “backbone” of probes across the entire genome are included on the array for analytical and quality control purposes. Rarely, off- target copy number variants causative of disease may be identified that may or may not be related to the patient’s phenotype. Only known pathogenic off-target copy number variants will be reported. Off-target copy number variants of unknown clinical significance will not be reported.
Detection is limited to duplications and deletions. The CGH array will not detect point or intronic mutations. Results of molecular analysis must be interpreted in the context of the patient’s clinical and/or biochemical phenotype.
Submit only 1 of the following specimen types
* Preferred specimen type: Whole Blood
Type: Whole Blood
In EDTA (purple top) or ACD (yellow top) tube: Infants (2 years): 3-5 ml
Older Children & Adults: 5-10 ml
Specimen Collection and Shipping: Refrigerate until time of shipment. Ship sample within 5 days of collection at room temperature with overnight delivery.
OrageneTM Saliva Collection kit (available through CEN4GEN) used according to manufacturer instructions.
Specimen Collection and Shipping: Store sample at room temperature. Ship sample within 5 days of collection at room temperature with overnight delivery.
Submit copies of diagnostic biochemical test results with the sample, if appropriate.
Sequence analysis is required before deletion/duplication analysis by targeted CGH array. If sequencing is performed by another third party provider, please submit a copy of the sequencing report with the test requisition.
- Sequencing analysis of the PKD2 gene is available (test code: 6647) and is required before deletion/duplication analysis.