What is ADPKD?
Autosomal dominant polycystic disease (ADPKD) is one of the world’s most common life-threatening genetic diseases. It is estimated to affect between one in 400 and one in 1,000 people – around seven to 17.5 million – worldwide, occurring equally in men and women and across all ethnic groups.
Most cases of ADPKD are caused by a mutation in genes called PKD1 and PKD2, which are involved in making a type of protein that is found in the cells of the kidneys and other tissues. This mutation occurs when the instructions the genes carry become ‘scrambled’, resulting in some of the cells’ processes not working as they should.
In ADPKD, the mutated gene causes a small number of kidney cells to reproduce abnormally, causing cysts – sacs filled with fluid – to form. Although these cysts usually start to develop soon after birth, most people don’t experience noticeable symptoms until adulthood, usually between the ages of 30 and 60.
Over time, the number and size of the cysts can increase; they can grow to the size a grapefruit. As the cysts multiply and get bigger, they cause the kidneys to enlarge as well. Both the cysts themselves, and the enlarged kidneys, can cause a range of symptoms and problems.
How do you get ADPKD?
ADPKD is a genetic disease, meaning it is passed on from parents to their children. All of the genes in your body come in pairs; one half of the pair is inherited from your mother and the other half, from your father. ADPKD is the result of a mutation in two genes called PKD1 and PKD2.
Because ADPKD has a dominant pattern of inheritance (hence the name), only one half of the gene pair needs to be affected by the mutation for the condition to occur. In other words, you only need to inherit a mutated gene from one parent to have the disease.
So, if either of your parents has ADPKD, you have a 1 in 2 (50%) chance of getting the disease. And, if you have ADPKD, there is a 1 in 2 (50%) chance that your children will have the disease (see diagram).
As a result, it is very common for several members of a family across generations to have ADPKD.
However, about 4 to 7% of cases of ADPKD are thought to be the result of a ‘spontaneous mutation’ – where neither parent has the disease, and therefore the mutant gene has spontaneously occurred.
As there are two genes involved in ADPKD there are two ‘types’ of the disease. Around 85% of people have ADPKD1 (caused by the PKD1 gene), while around 15% have ADPKD2 (caused by the PKD2 gene).
There is no difference in the symptoms, although ADPKD2 is generally the less aggressive form, which progresses more slowly with fewer cysts and less severe blood pressure problems. The average age for developing kidney failure as a result of ADPKD2 is 73, while in ADPKD1 it is 53. However, progression and symptoms are highly variable, even within families.
What are the symptoms of ADPKD?
Pain – usually in the abdomen (tummy) or side – is often the first noticeable symptom. It can range from moderate to severe and last from just a few minutes to several days. It can be caused by a number of things, including one or more of the cysts starting to bleed, a kidney stone getting stuck, or a urinary tract infection (UTI). Many people also experience back ache caused by the extra weight of enlarged kidneys and, sometimes, an enlarged liver and/or pancreas.
High blood pressure (hypertension) is commonly the first symptom of ADPKD to develop, but you may not know about it because it doesn’t usually have any outward signs until it reaches very high levels. As such it is only usually detected during routine tests. However, when symptoms occur they include headache, nose bleeds, blurred or double vision and shortness of breath. Around 33% of people with ADPKD will develop high blood pressure. If you have ADPKD it is very important that your blood pressure is monitored regularly and that high blood pressure is treated.
Haematuria (blood in the urine) usually occurs when a cyst ruptures or a blood vessel breaks. It is very rarely serious, most often passing within about a week without requiring any treatment.
Kidney stones are more common in people with ADPKD than in the general population, affecting around 20 to 30% of people with the disease. As their name suggests, kidney stones are hard, stone-like lumps that can develop in one or both of the kidneys.
The main function of the kidneys is to remove waste products from the blood, which are passed out of the body as urine. Occasionally the waste products build up and form crystals that, over time, can build up to form stones.
Kidney stones can vary in size. Small stones are often passed in the urine with no or very little pain, and you may not even notice them at all. Larger stones commonly get stuck as they pass through the urinary system, and can block the ureter (the tube that connects the kidney and bladder) or the urethra (the tube through which urine exits the body).
The most common symptom of kidney stones is severe, intense pain in your back or side of the tummy (and occasionally in your groin), which can last for several minutes or a few hours and is usually marked by pain-free periods in between. Other symptoms include feeling sick, being restless and unable to sit or lie still, and blood in your urine, often caused by the stone grazing the ureter.
Urinary tract infections (UTIs) are more common in people with ADPKD compared with the general population. They can occur in the upper urinary tract (the kidneys or ureters), or the lower urinary tract (the bladder or urethra). Symptoms of an upper UTI include a fever of 38°C/100.4°F or higher accompanied by uncontrollable shivering, nausea, vomiting and diarrhoea. Symptoms of a lower UTI include cloudy, unpleasant smelling urine, pain when urinating (dysuria), an urgent need to urinate, and needing to urinate more often.
When damage to the kidneys results in significantly reduced kidney function, you have what’s known as chronic kidney disease (CKD). This doesn’t usually have obvious symptoms until it is fairly advanced. When almost all of your kidney function has been lost, you have end-stage renal disease – or kidney failure. This usually happens over a long period of time and the symptoms of kidney failure include excessive fatigue and tiredness, blood and/or protein in your urine, feeling short of breath, nausea, feeling itchy, and needing to pass urine more often. Fluid retention also leads to swollen ankles, hands and feet. Women may experience disrupted periods while men may experience impotence.
Many people with ADPKD also develop cysts on their liver – a condition called polycystic liver disease (PLD), and sometimes on the pancreas. These organs do not usually become damaged, but the cysts can grow quite large. PLD is more common in women who have had multiple pregnancies – generally three or more – although it can also occur in men. If the cysts on the liver cause it to become very large, it can cause severe pain in the abdomen (tummy) and loss of appetite. Sometimes the cysts can press against the diaphragm (the large muscle that separates the chest from the abdomen), and make breathing difficult.
People with ADPKD have a slightly increased risk of developing brain aneurysms (8%) compared with the general population (2%), but they tend to run in families with a history of aneurysms or stroke. An aneurysm is a bulge in a blood vessel caused by a weakness in the wall of the blood vessel.
Some people with ADPKD develop a condition called left ventricular hypertrophy, where the left side of the heart becomes enlarged.
Hernias in the groin or abdomen (tummy) and diverticulitis may also occur. Diverticulitis is a digestive condition whereby small bulges develop on the lining of the large intestine (colon) and become inflamed or infected.
How is ADPKD diagnosed?
ADPKD is usually diagnosed from an ultrasound scan, which is used to detect and take ultrasound images of cysts. Other tests can be used to aid diagnosis, including computed tomography (CT) and magnetic resonance imaging (MRI) scans. Blood tests and blood pressure will usually be taken as well.
Once the diagnosis has been made, further scanning is often not routinely undertaken. Instead, the disease is monitored by tracking any changes in blood test results, including levels of a substance in the blood called creatinine, which indicates how well your kidneys are functioning.
Treatment for ADPKD
There is no cure for ADPKD and no treatment that will stop the condition progressing. However, there are a number of treatments and therapies that can help to alleviate the symptoms and prolong kidney function.
High blood pressure is one of the most common complications of ADPKD. It causes damage to the kidneys – which, in turn, makes high blood pressure worse – and increases the risk of heart disease and stroke. Therefore it is very important that your blood pressure is monitored regularly. You may be advised to do this yourself at home, using a small yet accurate, inexpensive machine. High blood pressure must be treated, and it can be controlled with the right treatment.
There is a range of different types of medications that are used to treat high blood pressure; your doctor will prescribe one for you based on your individual circumstances and symptoms, and you may need to take more than one type. Most blood pressure medications have side-effects but these are usually controllable – your doctor may prescribe a different type of medication for you if you are unable to tolerate a particular drug.
There are also a number of lifestyle changes you can make to help keep your kidneys as healthy as possible:
Smoking – if you are a smoker, try to quit or cut down. Smoking harms the blood vessels in the kidneys and accelerates kidney damage. There is also some evidence to suggest that smoking causes the cysts to form more quickly.
Diet – eat a balanced, healthy diet and in particular, try to limit your salt intake as salt can worsen high blood pressure.
Exercise – it is a good idea to take regular exercise and be as active as possible. This helps to prevent weight gain and can also help to control blood pressure.
Water – try to keep hydrated. There is some evidence to suggest that the body’s response to dehydration increases cyst growth, but this response can be minimised by drinking plenty of water.
Pain relief – if you have a lot of pain, check with your doctor what painkillers it is safe for you to take. You may be advised to avoid non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, which can cause scarring in the kidneys.
If you develop kidney failure, you will need to have renal replacement therapy (RRT).