Polycystic Kidney Disease

Autosomal-dominant polycystic kidney disease (ADPKD) is an inherited disorder usually presenting in adult life. It is characterized by the development of multiple renal cysts, variably associated with extrarenal (mainly hepatic and cardiovascular) abnormalities. ADPKD is by far the most common inherited nephropathy, with a prevalence rate ranging from 1:400 to 1:1000 in white populations. It accounts for 3-10% of all patients commencing regular dialysis in the West.

In about 85% of cases, the gene responsible ( PKD1 ) has been located on chromosome 16. A second gene, PKD2 , which has been mapped on chromosome 4, accounts for the vast majority of other cases. A third polycystic gene may exist. These genetic abnormalities are distinct from the autosomal recessive form of polycystic disease which is often lethal in early life.

The protein corresponding to PKD1 gene, polycystin I, appears to be an integral membrane glycoprotein involved in cell-to-cell and/or cell-to-matrix interaction. The protein corresponding to the PKD2 gene appears to function as an ion channel or pore. Polycystin could act as the regulator of the PKD2 channel activity.

How mutations in PKD1 and PKD2 lead to cyst development and other abnormalities is unclear. It is hoped that elucidation of the mechanism involved may pave the way to intervention which prevents or, at any rate, arrests or slows the manifestations of the disease.

Sign and Symptoms of Polycystic Kidney Disease

• acute loin pain and/or haematuria owing to haemorrhage into a cyst, cyst infection or urinary tract stone formation
• loin or abdominal discomfort owing to the increasing size of the kidneys
• subarachnoid haemorrhage associated with berry aneurysm rupture
• complications of hypertension
• complications of associated liver cysts
• symptoms of uraemia and/or anaemia associated with chronic renal failure.

The natural history of the disease is one of progressive renal impairment, sometimes punctuated by acute episodes of loin pain and haematuria, and commonly associated with the development of hypertension. The rate of progression to renal failure is variable. The determinants of progression are both genetic and non-genetic.

In the PKD2 form, renal cysts develop more slowly and end-stage renal failure (ESRF) occurs 10-15 years later than in the PKD1 form. Gender affects renal prognosis, males with ADPKD reaching end-stage renal failure 5-6 years earlier than females. There is a large variability in the age at ESRF within families, even between affected monozygotic twins.

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