Autosomal dominant polycystic kidney disease (ADPKD) acconts for about 10% of patients on dialysis in the U.S. and occurs in 1:400 – 1:2000 live births. As the disease is inherited in an autosomal dominant fashion, the question of genetic counseling often comes up (e.g., does my brother/sister/son/daughter also have ADPKD?) This is also a very relevant question in deciding whether or not a relative of a patient with ADPKD is an appropriate kidney donor: obviously, you wouldn’t want to take PKD kidney as a transplant, which would have poor results for both the recipient as well as the donor. Unfortunately, mutation screening is not useful in ADPKD since the PKD1 gene (accounting for about 85% of cases of ADPKD) is extremely large with multiple internal repeats, making it difficult to sequence, and furthermore the list of possible ADPKD mutations numbers in the 100s rather than being just a few common mutations.
To this end, a series of ultrasound criteria have been created and validated for screening. The criteria are based on the principle that the younger you are, the less likey you are to have cysts. These criteria have a very high sensitivity & specificity (apparently approaching 100%) in the appropriate clinical scenario. The criteria are as follows:
For patients with PKD 1 mutations:
age <30:>60: need at least 4 cysts per kidney.
For patients with PKD 2 mutations (which is generally less severe and delayed onset compared to PKD 1 mutations:
-need 4 or more cysts per kidney (ages 30-59) to reach a sensitivity of 96%.According to recommendations on Up To Date, patients less than 18 years of age should NOT be screened for ADPKD.