Cystinuria

What is cystinuria?

Cystinuria is a genetic disease (this means you are born with it) where you are more likely to develop kidney stones from cystine in the wee.

Wee is produced by our kidneys. The kidneys filter blood to remove extra water and waste products which our bodies do not need. The waste products then go on to become wee, and the substances our body needs are kept in our blood.

Cystine is an amino acid. These are building blocks for proteins and would normally be kept in our blood, however, in children with cystinuria, this leaks into the wee.

How do kidney stones develop in children with cystinuria?

Having too much cystine in the wee is a problem because it does not always stay dissolved and forms crystals (which can only be seen with a microscope) these crystals then clump together to form cystine stones.

This is more likely to happen if your child’s wee is more concentrated (looks dark yellow).

How do I prevent my child developing stones?

Children who have cystinuria need to drink plenty of water to dilute their wee and flush out the cystine to help prevent stones.

If your child is under 12 years old, we recommend they drink 2.5L of water per day. If your child is 12 years or older, we recommend your child drinks at least 3L of fluid per day.

They should also have a large drink at bedtime. Your child is most at risk of developing a stone at night time, so we advise they go to the toilet at least once overnight and have a big drink at this point too.

What are the treatments available for cystinuria?

Your child may be offered a medication called ‘potassium citrate’ to help prevent stones from forming. Potassium citrate acts to change the acidity of your child’s wee which means it is easier for the cystine to dissolve, preventing crystals from forming. Your doctor will talk to you about this if they think it will help your child.

Will my child need to follow a special diet?

It is important to encourage your child to have a healthy, low salt diet. Reducing the amount of salt (sodium) in your child’s diet will reduce the amount of cystine drawn into the wee.

It may also be helpful to reduce foods that are rich in methionine, as too much methionine can increase the risk of cystine stones. Foods that are high in methionine include:

• meat
• fish
• eggs
• milk
• cheese

Do not give your child these food items in excess, but do not cut these foods out completely as they help your child have a balanced diet, which is important to help you child grow. If you would like to speak with a dietician regarding either of these diet changes, please ask your doctor or nurse.

What are the risks of kidney stones and cystinuria?

Some children will never have renal stones. However, for those who have pain, renal stones are the most common symptom. This pain is usually felt in the back and side and comes in waves. Your child may be able to tell you where the pain is, however, younger children may just complain of tummy pain. Not all children experience this pain as some stones are tiny and pass into the wee without pain.

Children with stones are at a slightly increased risk of urine (wee) infections. It your child has symptoms of urinary tract infection (UTI) it is important they have their wee tested.

Will my child need regular check-ups and tests?

Most children with cystinuria live a healthy life. However, there is a risk that if they were to develop large kidney stones then this may affect how their kidneys work. If your child has had a renal stone in the past, we will need to see your child every year to make sure their kidneys are healthy and help prevent any more stones. They will need the following tests:

• blood pressure
• wee test
• height and weight

Occasionally we will do blood tests to help us measure the overall kidney function. We may also do an X-ray or scan to monitor your child for kidney stones, however, these will not be done every year, when they are needed will vary for each child.