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A 43-year-old woman with newly diagnosed hypertension reports persistent bilateral flank pain. She has a family history of “kidney problems.” On urinalysis, she is noted to have microscopic hematuria. An ultrasound and abdominal CT scan show bilateral polycystic kidneys (Figure 70-1).
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Polycystic kidney disease (PKD) is a manifestation of a group of inherited disorders resulting in renal cyst development. In the most common form, autosomal-dominant polycystic kidney disease (ADPKD), extensive epithelial-lined cysts develop in the kidney; in some cases, abnormalities also occur in the liver, pancreas, brain, arterial blood vessels, or a combination of these sites.
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- Most common tubular disorder of the kidney, affecting 1 in 300 individuals.
- Autosomal dominant in 90% of cases, rarely as an autosomal recessive trait.1
- Sporadic mutation in approximately 1:1000 individuals.
- ADPKD accounts for approximately 5% to 10% of cases of end-stage renal disease (ESRD) in the United States.
- Most frequently seen in the third and fourth decades of life, but can be diagnosed at any age.
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- ADPKD results from mutations in either of 2 genes that encode plasma membrane-spanning polycystin 1 (PKD1) and polycystin 2 (PKD2).2 Polycystins regulate tubular and vascular development in the kidneys and other organs (liver, brain, heart, and pancreas). PKD1 and PKD2 are colocalized in primary cilia and appear to mediate Ca2+ signaling as a mechanosensor, essential for maintaining the differentiated state of epithelia lining tubules in the kidney and biliary tract.3 These mutations result in many abnormalities including increased proliferation and apoptosis and loss of differentiation and polarity.4
- Few (1% to 5%) nephrons actually develop cysts.
- Remaining renal parenchyma shows varying degrees of tubular atrophy, interstitial fibrosis, and nephrosclerosis.
- Cysts are also found in other organs such as liver (Figure 70-2), spleen, pancreas, and ovaries. Liver cysts are found in up to 80% of patients with ADPKD.2 There is also an increased incidence of intracranial aneurysms (5% to 12%).
- Autosomal-recessive PKD (ARPKD) is the neonatal form of PKD that is associated with enlarged kidneys and biliary dysgenesis.3 The genetic mutation in PKHD1 (polycystic kidney hepatic disease 1) involves a protein, fibrocystin, that is also localized to cilia/basal body and complexes with PKD2. This large, receptor-like protein is thought to be involved in the tubulogenesis and/or maintenance of duct-lumen architecture of epithelium.
- Rare syndromic forms of PKD include defects of the eye, central nervous system, digits, and/or neural tube.3
- A variant of PKD is glomerulocystic kidney (GCK), which refers to a kidney with greater than 5% cystic glomeruli.5 This condition is usually diagnosed in young patients. Although PKD-associated gene mutations have been excluded in many cases, there is a familial form of GCK presenting with cystic kidneys, hyperuricemia, and isosthenuria (concentration similar to plasma)....