Polycystic Kidney Disease

What are the different types of polycystic kidney disease (PKD)?

There are three major types of PKD:

• autosomal dominant PKD (inherited)
• autosomal recessive PKD (inherited)
• acquired cystic kidney disease, or ACKD (non-inherited)

Autosomal dominant PKD (inherited)

• This is the most common inherited form of polycystic kidney disease, accounting for about 90 percent of all PKD cases.

• "Autosomal dominant" means that if one parent has the disease, there is a 50 percent change that the disease will pass to your child, and that both girls and boys are equally affected.

• In 25 percent of cases, there is no family history of PKD. You would not be at increased risk of having additional children with PKD, but your child with PKD would have a 50/50 chance to pass the gene on to her children.

• Autosomal dominant PKD is often called the adult polycystic kidney disease.

What are the symptoms of autosomal dominant PKD?

Symptoms usually develop between the ages of 30 and 40 (but they can begin as early as childhood), and may include:

• abdominal pain
• detectable abdominal mass
• pale color to skin
• bruise easily
• high blood pressure
• kidney stones
• aneurysms (bulging of the walls of blood vessels) in the brain
• diverticulosis (pouches in the intestines)
• urinary tract infections
• hematuria (blood in the urine)
• liver and pancreatic cysts
• abnormal heart valves

Autosomal dominant PKD may occur with other conditions including:

• tuberous sclerosis - a genetic syndrome involving seizures, intellectual disabilities, benign tumors, and skin lesions
• liver disease
• severe eye problems (cataracts or blindness)

Autosomal recessive PKD (inherited)

• Autosomal recessive PKD is a rare, inherited form thought to be caused by a different genetic flaw that the one responsible for autosomal dominant PKD.
• Parents who do not have the disease can have a child with the disease, if both parents carry the abnormal gene and both pass the gene to their child.
• If you are a carrier of this gene, there is a 25 percent chance, with each pregnancy, that your child will have this type of PKD.
• Males and females are equally affected.
• Autosomal recessive PKD is sometimes detected prenatally (before birth) using a fetal ultrasound.

What are the symptoms of autosomal recessive PKD?

Symptoms of autosomal recessive PKD can begin before birth. In most cases, the earlier the onset, the more severe the outcome. There are four types of autosomal recessive PKD, depending upon how old your child is when she begins experiencing symptoms:

• perinatal form- seen at birth
• neonatal form- seen within the first month of life
• infantile form- seen between age 3 and 6 months
• juvenile form- seen  after age 1

Symptoms of autosomal recessive PKD your child may experience include:

• urinary tract infections
• frequent urination
• low blood cell counts
• delayed development
• small stature
• protruding abdomen
• respiratory problems due to extreme kidney enlargement
• back pain
• pain in sides
• kidney cysts
• high blood pressure

Children born with autosomal recessive PKD may develop kidney failure within a few years and often experience the following:

• high blood pressure
• urinary tract infections
• frequent urination

The disease also usually affects the liver, spleen, and pancreas, resulting in low blood cell counts, varicose veins, and hemorrhoids.

Acquired cystic kidney disease or ACKD (non-inherited)

Acquired cystic kidney disease (ACKD) may develop in association with long-term kidney problems, especially if your child has kidney failure and has been on dialysis for a long time. Therefore, it tends to occur later in life, and is an acquired, not inherited, form of PKD.

Diagnosis

How is autosomal dominant Polycystic Kidney Disease (PKD) diagnosed?

Diagnosis of autosomal dominant PKD may include the use of imaging techniques to detect cysts on the kidney and other organs, and a review of the family history of autosomal dominant PKD into PKD1, PKD2, and PKD3.

How is autosomal recessive PKD diagnosed?

Diagnosis often includes ultrasound imaging of the fetus or newborn to reveal cysts in the kidneys. It may also be helpful to perform ultrasound examinations of the kidneys of your child's relatives.

Treatments

How is autosomal dominant Polycystic Kidney Disease (PKD) treated?

Your child's physician will establish a treatment protocol for autosomal dominant PKD after careful consideration of her symptoms and medical history. Treatment approaches may include:

• pain medication
• surgery to shrink cysts and relieve pain
• treatment for high blood pressure
• treatment for urinary tract infections
• dialysis
• kidney transplantation

What treatments are available for autosomal PKD?

Your child's physician will establish a treatment plan for autosomal recessive PKD only after careful consideration of her symptoms and medical situation. Treatment approaches may include:

• treatment for high blood pressure
• treatment for urinary tract infections
• hormonal therapy
• dialysis
• kidney transplantation

In polycystic kidney disease (PKD), fluid-filled cysts gradually take over the kidneys, causing them to fail and forcing patients to go on chronic dialysis — or wait for a kidney transplant. Hopes for a cure were raised when animal models showed promise in drugs inhibiting mTOR, a protein that coordinates cell growth and is over-active in PKD. But recent clinical trials brought disappointing results.

Probing deeper into the biology, Jordan Kreidberg, MD, PhD, and Shan Qin, MD, PhD, in our Division of Nephrology, opened up a new option. They found that the excess mTOR activation results from unwanted activity of a cell receptor called c-Met. Normally, after c-Met is activated, it is degraded, but in PKD, it never gets marked for degradation. When the researchers used an existing compound to block c-Met activity in mouse models, cysts were markedly fewer and smaller.

Kreidberg hopes that c-Met inhibitors, already being used in cancer trials, can eventually be tested in PKD patients. Since they are more specific in their action than mTOR inhibitors, they may be less toxic, and could potentially be combined with mTOR inhibitors and other drugs. “PKD is quite complex, with several regulatory pathways involved,” Kreidberg says. “It will likely benefit from sub-toxic doses of multiple agents, similar to cancer chemotherapy.” (Journal of Clinical Investigation, online September 13.)