Overview of Cystic Kidney Disease
Cystic kidney disease describes several conditions in which fluid-filled cysts form in the kidneys. Cysts generally develop in weak segments of the tubules that carry urine from the glomeruli. The cyst's growth displaces healthy kidney tissue. The kidneys expand to accommodate the cyst, which can weigh as much as 20 pounds.
Three factors determine cyst classification: its cause (acquired, inherited), its features (complicated, simple, multiple, single), and its location (outer [cortical] or inner [medullary] kidney tissue).
Cystic Kidney Disease Types
- Autosomal dominant PKD
- PKD type 1
- PKD type 2
- Autosomal recessive PKD
Secondary Cystic Kidney Disease
- Aquired cystic kidney disease (ACKD)
- Medullary cystic disease (inner kidney)
- Juvenile nephronophthisis (during adolescence)
- Medullary sponge kidney (deterioration of kidney with cysts)
- Renal cell cancer associated cysts
Autosomal dominant medullary cystic kidney disease (MCK) causes cysts to form in the inner tissue of the kidney and can develop at a very early age. Recessive juvenile nephronophthisis usually occurs later than MCK, but is associated with similar symptoms, including chronic renal failure and growth problems.
Small cysts in the collecting ducts of the inner kidney characterize medullary sponge kidney (MSK), which is associated with hematuria and kidney stones, but not chronic renal failure. Acquired cystic kidney disease (ACK) affects patients with chronic renal failure and causes hematuria, erythrocytosis (increase in red blood cells), and is associated with the development of cancer.
Incidence and Prevalence of PKD
Polycystic kidney disease (PKD) is the most frequently inherited disease; it affects approximately 600,000 people in the United States and over 12,000,000 worldwide. Most suffer from the autosomal dominant type. It is the fourth leading cause of kidney failure and causes 10 percent of all end-stage renal disease (ESRD), usually between the ages of 40 and 60. It affects men, women, and races equally.
PKD Risk Factors
If one parent has autosomal dominant PKD, there is a 50 percent chance the child will inherit it. If both parents have the gene for autosomal recessive PKD, there is a 25 percent chance their child will have the disease. If one parent carries the gene, the child will not develop it. Some people with PKD never develop symptoms and others develop cysts and hypertension in childhood.
Causes of PKD
PKD autosomal dominant types 1 and 2 are linked to a protein abnormality on chromosomes 16 and 4, respectively, and run in families. PKD autosomal recessive has been linked to chromosome 6. Causes of acquired cystic kidney disease (ACKD) are long-term disease (glomerulonephritis) and the scarring that often results from dialysis. ACKD is common among patients with chronic renal failure. Nearly all of those who use dialysis for more than 5 years develop ACKD.