Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disease in which fluid-filled lumps called cysts grow on the kidneys. Eventually the cysts can get big enough to damage the two blood-filtering organs.
ADPKD passes down from parents to their children. Often, it affects many people in the same family.
If one of your parents has this disease, you could have it too. And because ADPKD can lead to kidney failure, it's important to learn your family history and know what your chances are of getting the disease.
If you are at risk for ADPKD, your doctor can test you for it. If you have it, they can treat you to slow the kidney damage.
Which Genes Cause ADPKD?
Gene changes called mutations cause ADPKD. Most people with it have changes to the PKD1 or PKD2 gene. They hold the instructions your body needs to make proteins that help control the growth of kidney cells. When one of these genes has a mutation, kidney cells grow abnormally and cysts form.
PKD1 causes 85% of ADPKD cases. PKD2 causes the other 15%. People with the PKD1 gene mutation have more severe symptoms. Their kidneys also go into failure faster than those with the PKD2 mutation.
How ADPKD Passes Through Families
The genes that cause ADPKD are autosomal dominant.
Autosomal means the gene is on one of the numbered chromosomes. Those are thread-like structures in each of your cells that hold your genes. You have 22 pairs of numbered chromosomes called autosomes, and one pair of sex chromosomes (X and Y).
Dominant means you only need to inherit the gene from one of your parents to get the disease. The ADPKD gene dominates over the normal gene from your other parent.
What If No One in Your Family Has It?
It is possible to be the only one in your family with ADPKD. About 10% of people who have ADPKD don't have any relatives with the disease.
One of the genes that cause ADPKD can change on its own. Your doctor may call this a new or spontaneous mutation. No one knows what causes the change. Once you have the gene mutation, you can pass it to your children, even if you didn't inherit it from your parents.
Should I Get Tested?
You may want to if ADPKD runs in your family. Often, you won't have any symptoms until you're in your 30s or older. The only way to know if you have ADPKD earlier is with a screening test or a genetic test.
An ultrasound is the most common and cheapest way to screen for PKD. It can show cysts on your kidneys before you have symptoms. During this test, a technician places a device called a transducer on the skin over your kidneys. The transducer releases sound waves that bounce off of your kidneys. A computer then converts those sound waves into a picture of your kidneys.
Computed tomography (CT) and magnetic resonance imaging (MRI) scans are other imaging tests that can detect cysts. They're more accurate than ultrasound, but sometimes they use contrast dye, which could harm your kidneys.
Genetic tests are another way to find out if you have this disease, but they are expensive. There are two kinds of gene tests for PKD. Both involve a blood test:
Gene linkage compares segments of your DNA with those of family members who have ADPKD. Both you and a few of your relatives will need to provide blood samples. This test is 99% accurate at showing whether you have the disease.
Direct DNA sequencing checks your DNA for the PKD1 and PKD2 genes. It isn't as accurate as gene linkage, but it may be an option if your family members don't want to be tested.
Not everyone needs genetic testing. Your doctor might recommend it if you have a family history of PKD and your ultrasound result was negative. They also might suggest it if you want to donate a kidney to a family member.
If ADPKD runs in your family, it can be helpful to meet with a genetic counselor. They explain your test options and help you understand the results.
The counselor can also tell you what a positive test result could mean for your family, and if they need testing. They can also offer advice on how to protect your kidneys if you do have one of the faulty PKD genes.