Cystinosis

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Cystinosis is caused by a problem in the CTNS gene. This gene produces the cystinosin protein, which transports a form of amino acid called cystine from one part the cell to another. This process is needed to ensure that cystine does not build up to dangerous levels in your cells. 

 If you have a problem in the CTNS gene, you will not produce enough of the cystinosin protein. Therefore, you will unable to remove excess cystine from your cells and this causes a build-up that forms crystals. These crystals damage the cells. This is particularly prominent in the kidneys and the eyes, although other parts of the body may also be affected. 

Cystinosis occurs in between 1 in 100,000 people and 1 in 200,000 people. However, more cases have been reported in the Brittany region of France, at a rate of around 1 in 26,000. This is considered to be due to a number of consanguineous marriages. 

In the UK, there are 2-3 new cases of Cystinosis diagnosed every year. 

There are three different types of Cystinosis, and the signs and symptoms of the disorder depend on which type you have. 

 The most common type is Infantile Nephropathic Cystinosis, which accounts for 90-95% of cases. Symptoms begin in the first few months of life and get progressively worse. They include: 

• Poor growth 
• Kidney damage 
• Soft, bowed bones (hypophosphatemic rickets)
• Increased urination 
• Constant thirst 
• Dehydration 
• Abnormally acidic blood (acidosis) 
• Build-up of crystals on the cornea causing eye pain and sensitivity to light 

 If you do not receive treatment, you are likely to experience complete kidney failure by the age of 10. Without treatment, you will develop more symptoms in adolescence, including: 

• Muscle deterioration 
• Blindness 
• Inability to swallow 
• Diabetes 
• Thyroid and nervous system problems 
• Infertility in males 

 The second type of the disorder is Nephropathic Juvenile (or Intermediate) Cystinosis, which accounts for 3-5% of cases. This type has the same symptoms, but they do not appear until adolescence. If left untreated, complete kidney failure will occur in late teens to mid-twenties. 

 The third type of Cystinosis is called Non-Nephropathic Cystinosis (also known as Ocular or Benign Cystinosis). Making up 1-2% of cases, if you have this form of the disorder, you will experience eye-related symptoms, including the build-up of crystals on the cornea that can cause eye pain and sensitivity to light, but not any of the other signs and symptoms. This can be diagnosed at any age. 

 Life expectancy is dependent on the form of Cystinosis you present with. For Infantile Nephropathic Cystinosis, which is the most severe form of the disorder, new treatments mean that life expectancy has greatly improved. Once, children did not live beyond 10 years old, however many can now expect to live into their 40s or 50s and lead full lives.  

Cystinosis is diagnosed using a specialised blood test and a specialised urine test. A genetic test will be conducted to confirm the diagnosis. 

 There are a wide range of different disorders that have similar symptoms to Cystinosis, for example: 

• Lowe syndrome 
• Wilson disease 
• Tyrosinemia type I 
• Galactosemia 
• Glycogen storage diseases 

Medication is available that can help to reduce the severity of Cystinosis and delay the need for more invasive treatments, such as a kidney transplant, until adulthood. It reduces cystine levels in your organs’ cells so that they are less likely to get damaged. There are also eye drops available that can reduce the amount of cystine in your corneas. It is important that this treatment is commenced as soon as possible to help prevent serious organ damage and encourage normal growth. This is why it is important to get an early diagnosis. 

 Treatment also focuses on managing the symptoms of Cystinosis. This includes vitamin supplements, management of dehydration, and growth hormone therapy. More invasive treatments may include kidney and/or thyroid transplants, which can increase life expectancy. 

Cystinosis is inherited from both parents in an autosomal recessive inheritance pattern. This means that both parents are carriers of the disorder through their genes.  

All genes come in pairs. Carriers of Cystinosis have one working CTNS gene and one faulty gene. Children inherit one gene from each parent to make their pair. Whether you have Cystinosis depends on the genes you inherit: 

•  There is a 50% chance that the child will inherit one faulty and one working gene, which means they will also be a carrier. 
• There is a 25% chance that the child will inherit two working genes and not inherit or carry the faulty gene. 
• There is a 25% chance that the child will inherit two faulty genes, which means they will have Cystinosis. 

 If you think you, or somebody in your family, may have Cystinosis, or that you may be a carrier, contact your medical team who may refer you for genetic testing. 

Thank you to Cystinosis Foundation UK for helping provide this up-to-date information.

Established in 1998, CFUK is staffed by volunteer trustees who work around full-time jobs, families and other commitments to deliver the key aims of improving patients outcomes, treatments and research, informing patients, families and healthcare professionals and sharing stories, experiences and answers.

CFUK Contact Details:

• Email advice@cystinosis.org.uk
• Website https://www.cystinosis.org.uk/

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