Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease. It affects all racial groups and occurs in 0.2 per cent of the population.
It is typically considered an adult disease because most patients are either diagnosed or receive treatment during adulthood. As a result, it used to be called ‘adult polycystic kidney disease’. Nevertheless, it is an inherited disease so children can be born with the genetic problem, although they may not show signs until later in life.
What are the symptoms of ADPKD?
Children can be affected in the same way as adults. ADPKD usually causes fluid-filled cysts to form in the kidneys, which press on the surrounding normal kidney tissue and stop the kidney working properly.
Fortunately, if cysts are diagnosed, it is usually only a small number and kidney function in the vast majority of children is normal or only mildly impaired. Very rarely do children experience complications, such as increased blood pressure, pain, blood or protein in the urine or kidney stones.
However, in a very small number of children, end-stage kidney failure can occur, requiring dialysis or transplantation. It is extremely unusual for children to have complications from ADPKD outside the kidney, such as aneurysms (ballooning of a blood vessel) in the brain. These aneurysms can potentially rupture, leading to severe bleeding inside the head. This complication has not been reported in children, but some experts recommend screening for it in late adolescence, if other family members have aneurysms.
How is ADPKD diagnosed?
It is now possible to check cyst formation in the kidneys using a straightforward ultrasound scan. Since we have started doing this during the past 10 years, we have realised that some children of affected parents already have cysts in early childhood and in very rare instances, cysts are already seen on prenatal ultrasounds.
However, screening for cysts is not routinely done and often cysts are detected by chance when an ultrasound or other scan is carried out for an unrelated reason.
What causes ADPKD?
Human beings have about 30,000 to 40,000 different genes, each of which has a function in making an individual person. The genes are arranged in pairs (one of the pair from each parent) on 23 chromosomes.
Inevitably, some of these genes are faulty. Sometimes, a normal gene can overcome a faulty one, but if both genes in the pair are faulty, the genetic instructions cannot work. In ADPKD, only one parent needs to pass on the faulty gene for the child to develop the disease. Each child from the partnership has a 50 per cent chance of inheriting the disease and a 50 per cent chance of not inheriting it.
What treatments are available?
There are no specific treatments that stop cysts developing in children at the moment, but there are trials of promising new treatments in adults, for which we await the outcome. Therefore, the only proven, safe treatment that we can currently offer to children is directed at specific symptoms, such as elevated blood pressure.
High blood pressure not only accelerates the decline in kidney function but also affects other organs, such as the heart and blood vessels. In one study, half of all children with ADPKD have hypertension (high blood pressure). Moreover, enlargement of the heart muscle was already seen in children whose blood pressure was above average but still in the normal range. Yet this increase in heart size could be prevented with adequate treatment.
It is therefore recommended that children of affected parents have their blood pressure checked once a year from about school age, when blood pressure measurements are more easily obtainable and accurate. If blood pressure is elevated, your child should be seen by a kidney specialist (paediatric nephrologist) to start appropriate treatment.
Should my children be tested?
The decision to test your children for the disease should be carefully discussed within your family and with your or your child’s doctor. The main argument against testing is that, in the absence of an effective treatment, establishing the diagnosis will provide no immediate benefits, but will burden your child with the knowledge of having a serious disease and this may affect his or her ability to obtain life or health insurance, mortgage or future occupation.
By holding off testing, you can let your child decide when he or she is old enough to do so, whether they wish to know the diagnosis. The main argument for testing is that it will provide certainty, so that children who have not inherited the disease can stop worrying about being affected and do not need extra visits to the doctor. Those shown to have inherited the disease can start to come to terms with the diagnosis.
You will need to consider these arguments in order to find the right solution for your family. Currently, testing of children is not routinely recommended, but this would obviously change if effective treatment became available.
How can my child be tested?
If you want to have your child(ren) tested, there are different ways to do it.
This is the most common method used as it is easily available. However, it can be misleading, as single cysts can occur in people without ADPKD. Moreover, the first cyst can occur as late as the fourth decade of life so the absence of cysts in children does not rule out the presence of the disease. In one study, 62 per cent of children affected by ADPKD had cysts on renal ultrasound by five years of age and 78 per cent by 18 years of age.
This is the most accurate method. If a mutation in an ADPKD gene is identified in the family, the child can easily be tested for the presence of this mutation. In cases where no mutation is identified, something called linkage analysis can be done if two or more affected family members are available. This analysis uses markers on the chromosomal regions that contain the ADPKD genes to discriminate between the two copies to identify which one is likely to harbour the mutation and if the child has inherited that particular copy. Genetic testing for ADPKD is very labourintensive and expensive due to the complexity of the affected genes and so is currently not performed routinely. This is likely to change in the near future as progress in the technology will make it much easier and cheaper to carry out these tests.
If you have any questions, please call Eagle Ward on 020 7829 8815.