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Polycystic Kidney Disease

Explain the genetic aspects of adult polycystic kidney disease?
Adult polycystic kidney disease is a hereditary disorder with autosomal-dominant transmission. There is virtually 100% penetrance by age 80, with perhaps a slightly less penetrance before that age. However, a positive family history is not always obtainable, possibly because other family members with the disease die of other causes prior to the disease being diagnosed or because the patient lacks knowledge of the family history. Although the actual gene responsible for transmission is unknown, it has been located to the short arm of chromosome 16. Spontaneous mutations occur infrequently « 10% of the time) and may also contribute to the lack of a family history .
 
How many individuals are affected?
The incidence is approximately I in every 1000-1250 live births, and currently 500,000-600,000 Americans have the disease. Patients with adult polycystic kidney disease account for 5-10% of all patients with end-stage renal disease.
 

Does adult polycystic kidney disease occur only in adults?

No. Although the highest incidences occur between ages 45 and 65 and most patients exhibit manifestations of the disease after age 30, the disease can occur at all ages and has even been diagnosed in utero.
 
Does adult polycystic kidney disease affect organs other than the kidney?
Yes. Once again, the term .. adult polycystic kidney disease" underemphasizes the true magnitude of the systemic nature of the disease. Cysts have been found in many other organs, including the liver (most commonly), pancreas, sl leen, arachnoid, thyroid, ~seminal vesicles, and ovaries. Other manifestations include intracranial (berry) aneurysms, mitral valve prolapse and other cardtac valvular abnormalities, and colonic diverticula.
 
What causes adult polycystic kidney disease?

While the exact cause remains unknown, several theories are favored:
An abnormality in the renal tubular basement membrane with altered compliance of the tubular wall allowing cyst formation
Epithelial hyperplasIa wIth resultant tubular obstruction and cyst formation
Abnormal synthesis or metabolism of tubular basement membranes with an alteration in the protein composltton of the extracellular connective tissue mat  x The latter eory appears to st escribe the extrarenal manifestations seen in patients with polycystic kidney disease and its function may be necessary before the pathogenesis of the disease is fully understood.
adult polycystic kidney disease. However, identification of the gene responsible for adult

 
How is adult polycystic kidney disease diagnosed?

Although the diagnosis may be suspected due to a strong family history, characteristic symptoms, I hysical findings, or radiographic imaging is used to confirm the diagnosis. The radiographic hallmark of adult polycystic kidney disease tS btlateral renal enlargement with multiple cysts of varying sizes.
 

. Which radiographic tests are best for making the diagnosis?
Renal ultrasonography provides an excellent, inexpensive screening tool for diagnosing adult polycystic kidney disease. It has the advantage of avoiding radiation and the need for contrast, but it may be slightly less sensitive in the younger patient. Computed tomography (CT) demonstrates excellent sensitivity and may provide better imaging of other organs, including the liver, pancreas, and spleen. Although intravenous urography will show the characteristic features of bilateral renal masses with distortion of the collecting system, the results are often equivocal and further study is required with either ultrasound or CT. The addition of nephrotomograms to the intravenous urogram increases the sensitivity.
 
Describe the associated physical findings?

Flank mass represents the most common physical finding in patients with adult polycystic kidney disease. However, patients with severe hydronephrosis (especially from ureteropelvic junction obstruction) as well as other large renal masses (angiomyolipomas, renal cell carcinoma, etc.) may also have detectable flank masses. Some patients with significant extrarenal involvement of adult polycystic kidney disease may have hepatomegaly or splenomegaly detected on physical examination.
 

How is adult polycystic kidney disease treated?
Treatment is largely directed at the individual complications. Most episodes of bleeding resolve spontaneously, although an occasional life-threatening episode will require intervention such as angiographic embolization or surgery. The hypertension should be aggressively treated, and the angiotensin=converting enzyme_(ACE) inhibitors may be of particular benefit. Analgesics usually provide pain relief, and appropriate antimicrobials are employed for urinary tract infections. As renal insuffic~r.y progresses, conservative measures such as low protein diet and phosphate binders are instituted. Many patients ultimately require dialysis or transplantation.
 
 

Can surgery prevent the progression of renal failure?
Except in the rare case in which ureteral obstruction is caused by an enlarged cyst, surgical decompression of the cyst does not appear to affect renal function. Surgical decompression of the cyst can be dramatic in relieving intractable pain and is more effective than percutaneous aspiration of the cyst for this purpose. Also, surgical cyst decompression only rarely appears to improve blood pressure substantially.
 
 

Are dialysis and transplantation effective for patients with adult polycystic kidney disease?
Yes. Despite these patients being slightly older at the time of development of end-stage renal disease, the results of dialysis and transplantation are at least as good as in other nondiabetic patients.
 
 

If adult polycystic kidney disease is hereditary, can family members safely donate kidneys?
Yes. With appropriate genetic studies and ultrasound screening, family members, especially those beyond age 25-35, can be accurately assessed for the presence of adult polycystic kidney disease. In the absence of any evidence for this disease, such family members may safely donate a lmlney for transplantation.

 
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