Polycystic kidney disease (PKD) is an inherited disorder of the kidneys in which an abundance of fluid-filled cysts develops and enlarge in the kidneys, impairing normal structures and function. In some individuals, the disease may remain stable or even asymptomatic.
In polycystic kidney diseases (PKD), innumerable cysts develop in the kidney causing progressive loss of kidney function and other complications.
PKD are inherited disorders caused by several specific gene mutations. More common is the dominant form of PKD (DPKD) that only requires a mutation in one of our pairs of genes (the pairs comprising one gene from the mother and the other from the father). To have the recessive form (APKD), its gene must be inherited from both parents.
APKD is associated with a high risk of infant mortality and poor lung function at birth. DPKD is usually not diagnosed until early to mid-adulthood and leads to kidney failure in middle-aged and older adults.
Symptoms of DPKD include pain in the back or flanks (over the kidneys), blood in the urine, high blood pressure, kidney stones, and chronic headaches.
When suspected, the diagnosis can be confirmed by radiological studies, most often a kidney ultrasound.
The majority of mothers with DPKD will have uneventful pregnancies and deliver healthy infants. However, there is a 50% chance that the infant will have DPKD. New approaches to genetic testing can identify embryos without the mutation before implantation.
Treatments for DPKD include managing symptoms, controlling blood pressure, treating chronic kidney disease as it progresses and dialysis and/or kidney transplantation if necessary.
In recent clinical studies, tolvaptan drug treatment has been shown to reduce the size of the cysts, the enlargement of the kidneys, and slow the progression of kidney dysfunction.
But the majority of people have a significant risk of progressive kidney dysfunction that ultimately leads to dialysis or kidney transplantation.
PKD and genetics
There are two inherited types of PKD. Each is caused by characteristic gene mutations. The more common type of PKD is a genetic “dominant” disorder (DPKD), and it occurs when the mutated gene is inherited from only one parent.
The other less common form of PKD is genetically “recessive” (RPKD); both parents must convey the gene mutation. When the dominant mutation is carried by one parent, 50% of their children will be affected. With an inheritance of the recessive gene from both parents, 25% of their children will develop the disease. DPKD is around 40 times more common than RPKD.
Common symptoms of DPKD
The majority of individuals with DPKD are diagnosed between the ages of 30 and 50 years. Less commonly, it may first be identified in children and adolescents.
Most cases have a family history of DPKD. Although DPKD may remain silent or progress slowly, around one half cases ultimately require dialysis and/or kidney transplantation.
Signs and symptoms include:
- pain in your sides or back.
- blood in your urine.
- high blood pressure.
- kidney stones.
- a large mass felt in the abdomen or side.
- chronic headaches (possibly due to high blood pressure or brain aneurysms).
- advanced chronic kidney disease or kidney failure.
Diagnosis of DPKD
The initial evaluation will confirm the diagnosis, evaluate kidney function, and determine whether there are other associated health problems. This will include:
- An abdominal examination to identify enlarged kidneys.
- Blood pressure measurement since hypertension is common in DPKD and may, among other things, cause problems with the heart and brain, in particular.
- A comprehensive metabolic panel (CMP) of the blood to estimate kidney function and identify mineral and electrolyte imbalances frequently seen in chronic kidney disease.
- A complete blood count (CBC) for anemia which often develops in patients with kidney disease. This is because sick kidneys are able to produce an adequate amount of the hormone that stimulates red blood cell production (erythropoietin).
- A urinalysis to detect significant protein, microscopic blood, or signs of a UTI. DPKD kidneys often also have limited ability to concentrate the urine; your doctor may want to do the test on a specimen from the first void in the morning when the urine should be most concentrated.
- A kidney (renal) ultrasound. This is a completely painless and safe radiology test that uses high frequencies of sound to obtain images of the kidney. You may be more familiar with the use of ultrasound to assess the developing baby during pregnancy. Polycystic kidneys are found to be substantially enlarged (Figure), containing a massive number of different sized cysts.
- An MRI or a CT scan may be done when there is a need for clarification of the diagnosis and greater detail of a kidney’s state. These studies also can show the presence of cysts in other organs, particularly the liver and biliary tract. An MRI of the brain may be done when there are symptoms or family history of a possible brain aneurysm.
Pregnancy and PKD
Most women with dominant PKD will experience uneventful pregnancies and deliver healthy newborns, particularly those that have normal kidney function and no hypertension. By contrast, about one third of babies with recessive PKD will die in the newborn period.
Those who do survive may have a good chance to reach adulthood although the deterioration of kidney function will require lifelong medical care. Pre-existing hypertension will need close monitoring because the blood pressures may worsen during the pregnancy. Preeclampsia (toxemia) may also occur. This is a serious condition for both mother and baby.
Recent data suggest that advanced preimplantation genetic testing can identify in vitro fertilized embryos that do not carry the DPKD genes. Selection of these embryos can greatly reduce the risk of having a child with DPKD.
Complications of DPKD
The main complications of DPKD are:
- Development of progressive chronic kidney dysfunction or kidney failure requiring closely monitored medical care and dialysis or kidney transplantation.
- Hypertension (high blood pressure) of varying severity. The risk of hypertension increases with greater numbers of cysts and larger kidneys. Uncontrolled hypertension can cause damage to the heart and brain. It also causes further kidney injury.
- Cyst development in other organs including the liver, pancreas, thyroid gland, and male reproductive tract (possibly causing infertility). Cysts may also occur in the membrane that covers the brain and spinal cord. These rarely cause complications.
- Brain aneurysms occur when the wall of an artery becomes weakened, bulges out, and may result in hemorrhage. Although these are clinically significant in only a minority of DPKD patients, they are nonetheless of great clinical importance. The presence of hypertension and a family history of brain aneurysms are risk factors.
There is no cure for DPKD except kidney transplantation, if warranted. DPKD may require medications to manage symptoms, such as pain, headaches, hypertension, and urinary tract infections. If a brain aneurysm is found, a neurosurgical consultation should be obtained.
The effectiveness of a number of drugs on the progression of DPKD has been investigated. One gaining considerable attention is tolvaptan. A group of recent clinical studies shows that tolvaptan can slow both the growth of kidney cysts and the rate of progression to kidney failure. The drug appears to slow the decline of kidney function in DPKD among other kidney diseases.