Autosomal dominant polycystic kidney disease (ADPKD)
ADPKD is an autosomal dominant disorder characterised by the presence of cysts in both kidneys. The cysts are numerous and fluid-filled, resulting in massive enlargement of the kidneys, often with progression to renal failure. The disease can also affect the liver, pancreas, and rarely, the heart and brain.
ADPKD has an incidence of 1/1000 and account for approximately 5% of patients with ESRF requiring replacement therapy.
In ~85% of cases, it is caused by mutations in the PKD1 gene on chromosome 16 which codes for the protein polycystin 1. 15% of cases are due to mutations in the PKD2 gene. Renal tubules dilate initially and fill with glomerular filtrate, and then separate from the functioning nephron, filling with secreted rather than filtered fluid, thereby resulting in cyst formation. Haematuria is a result of haemorrhaging cysts. Vascular sclerosis and interstitial fibrosis eventually develop through unknown mechanisms, and about 40% of patients develop renal failure by age 60.
Common extra-renal manifestions are as follow:
- Hepatic cysts – frequently occur in most patients, but their presence does not affect liver function.
- Pancreatic and intestinal cysts, colonic diverticula, and inguinal and abdominal wall hernias – occur in higher incidence in ADPKD patients.
- Valvular heart disorders – in 25-30% of patients
- Aortic regurgitation – may result from aortic root dilation due to arterial wall changes
- Coronary artery aneurysms
- Cerebral aneurysms – in approximately 4% of young adults and up to 10% of elderly patients; intra-cerebral haemorrhage accounts of accounts for 15% of deaths
Initially in most instances, ADPKD does not cause symptoms. In those who go on to become symptomatic, this occurs by the end of the second decade in life, where flank pain, abdominal and lower back pain due to cystic enlargement and symptoms of infection are the most common complaints. Valvular replacement may be required in individuals who have developed heart failure secondary to valvular disorders, although cardiac involvement in itself may be asymptomatic. Haematuria, hypertension and proteinuria are common signs. Anaemia is less frequent compared to other types of CRF because erythropoietin production is preserved. In advanced PKD the kidneys become grossly enlarged and palpable, causing fullness in the upper abdomen.
Diagnosis is made on USS, and less frequently on CT or MRI, or through genetic testing.
ESRF typically occurs aged 40-60, with 50% of 75 year old PKD patients requiring renal replacement, i.e. dialysis or transplantation.
Treatment of the condition is based on controlling risk factors, e.g. strict control of BP.