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How are cysts formed?

ADPKD is characterised by the growth of numerous cysts in the kidneys, and sometimes in other organs.

Contents

What is a cyst?

Figure 1: Plastic-embedded 1micron section of a pre-dialysis ADPKD kidney cyst.

In ADPKD, cysts develop over time, and so might not be present in children or young adults. Therefore, if you’re under 30, it may not be possible to use ultrasound to confirm a diagnosis of ADPKD, even if you have a family history of the condition. You may be advised to have ultrasound scans periodically repeated in the future, to check for cysts as you get older. Similarly, ruling out a diagnosis of ADPKD in people under 40 years is difficult. However, by age 40, a diagnosis of ADPKD can be ruled out in individuals who don’t have multiple kidney cysts.

Genetic tests

ADPKD is caused by a faulty (mutated) gene. Mutations in one of two genes can cause the disease: PKD1 or PKD2.

Genetic testing is usually performed on a sample of blood. It checks the DNA in this blood sample for faults in the PKD genes. Genetic testing is the most accurate way of making a diagnosis of ADPKD. It’s available through the NHS, but it’s not required to make a diagnosis of ADPKD in most people.

To find out more about genetic testing – and whether it might be appropriate for you – see our web page ‘Genetic counselling and genetic testing in ADPKD’.

Figure 2: Diagram of a normal nephron comprised of a glomerulus (to filter the blood) attached to a long nephron with specialised regions.
(Wilson, P., New Engl. J. Med. 350: 151-164, 2004.)

Figure 3: During development of ADPKD nephrons, cystic outpushings can arise from every segment of the nephron. These close off from the nephron of origin early in the developmental process, rendering that nephron non-functional.

(Wilson, P., New Engl. J. Med. 350: 151-164, 2004.)

How do cysts enlarge?

Once cysts close off from the nephron and become separated, they continue to enlarge by increased cell proliferation, fluid secretion and changes to the extracellular matrix (tissue which supports the cells) surrounding the nephron.

How does cyst growth affect kidney function?

As more and more cysts are formed, fewer and fewer nephrons can function properly. Fortunately the kidney has a large functional reserve capacity and does not need to use all nephrons at once. Therefore, it is not until about 60% of nephrons have stopped functioning (due to cyst growth) that the kidneys begin to fail.

Where else can cysts form?

The most common site, other than the kidney, in which cysts form is the liver, due to excessive growth (proliferation) of the cells lining bile ducts. This causes the liver to enlarge. Although fortunately liver functionality is not usually impaired, this can lead to pain, breathlessness and reduced mobility.

Authors and contributors

Written and reviewed by:
Professor Patricia Wilson, UCL Centre for Nephrology, Royal Free Hospital, London

With thanks to all those affected by ADPKD who contributed to this publication.

UNDER REVIEW

Disclaimer: This information is primarily for people in the UK. We have made every effort to ensure that the information we provide is correct and up to date. However, it is not a substitute for professional medical advice or a medical examination. We do not promote or recommend any treatment. We do not accept liability for any errors or omissions. Medical information, the law and government regulations change rapidly, so always consult your GP, pharmacist or other medical professional if you have any concerns or before starting any new treatment.

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The PKD Charity Helpline offers confidential support and information to anyone affected by PKD, including family, friends, carers, newly diagnosed or those who have lived with the condition for many years.