What is cystinosis?
Cystinosis is a rare, inherited genetic condition that mostly affects children, though more people are living into adulthood as treatment improves. It’s estimated to affect between 1 in 100,000 to 200,000 people.
Cystinosis is caused by the buildup of the amino acid cystine in all cells in the body, affecting the:
- bone marrow
Read on to learn more about this condition.
Types of cystinosis
There are three main types of cystinosis.
1. Nephropathic cystinosis
Nephropathic cystinosis, also known as infantile cystinosis, is the most common and severe form of the disease. Symptoms normally appear in infants between the ages of 3 and 6 months. If left untreated, children with this condition typically develop kidney failure within the first 10 years of life. With treatment, end-stage renal failure is often delayed.
One of the most notable symptoms in infants is failure to thrive. Infants with this condition are typically shorter and weigh less than other babies their same age. They may also have delays in walking and appear to be more fussy than other babies.
Symptoms relating to damage to the kidneys may include:
- poor appetite
- extreme thirst
- frequent urination
- signs of dehydration, including dry lips or skin, irritability, sunken soft spot (fontanel) on a baby’s head, drowsiness
- softening of bones, which is known as rickets
Symptoms unrelated to damage to the kidneys include:
- eye pain or discomfort associated with bright lights
- blurred vision
- muscle wasting
- feeding, swallowing, or breathing difficulties
- symptoms of hypothyroidism
Children with this condition typically have normal cognitive ability.
2. Intermediate cystinosis
Intermediate cystinosis is sometimes called juvenile cystinosis. This is a rare form of cystinosis, and has similar features of nephropathic cystinosis. Symptoms begin to appear at a later age, usually between 8 and 20 years old. Symptoms are also typically less severe than symptoms in nephropathic cystinosis.
Teenagers with this condition may have delayed puberty. Males may produce reduced amounts of testosterone, which can further affect puberty.
3. Non-nephrophatic cystinosis
Non-nephropathic cystinosis is also known as adult cystinosis because it affects people later in life. The condition is usually discovered during an eye exam, because symptoms usually only affect the eyes. Kidney disease is not a complication of this type of cystinosis.
Which conditions are associated with
Cystinosis is the most common cause of Fanconi syndrome. Fanconi syndrome is a rare condition of the kidney in which minerals, salts, and amino acids are excessively lost in the urine.
Fanconi syndrome is also associated with rickets due to the loss of phosphate. Rickets is a skeletal disorder that leads to softening of the bones. It’s usually caused by a deficiency of vitamin D, but in those with cystinosis it’s from the loss of phosphate.
What causes cystinosis?
Cystinosis is a genetic condition. To develop it, a child must inherit a faulty CTNS gene from both of their parents. That means that both parents must be carriers, but being a carrier doesn’t mean your child will inherit this condition.
If both parents carry the gene, there’s a 25 percent chance that their child will have cystinosis. If the child inherits one unaffected gene and one affected gene, then they will be a carrier of cystinosis, but they will not have the disease or any of its symptoms.
The CTNS gene is responsible for the production of a lysosomal transport protein known as cystinosin. Cystinosin helps get cystine out of the cells. In cystinosis, cystine isn’t adequately transported out of the cells, so it builds up and crystalizes. This causes the problems associated with the disease.
How is cystinosis diagnosed?
If your child’s doctor suspects cystinosis, they’ll take a blood test to measure cystine levels inside the white blood cells. This is known as a white blood cell cystine test.
If your child has eye discomfort, their doctor will perform an eye test. A slit lamp test will typically show cystine crystals on the cornea in those with cystinosis.
Doctors may also request a genetic test to determine the presence of the CTNS gene or the particular gene mutation.
How is cystinosis treated?
You may see a number of different specialist doctors, including a:
- nephrologist (kidney specialist)
- ophthalmologist (eye specialist)
- endocrinologist (hormone specialist)
- clinical geneticist
Cysteamine (Cystagon, Procysbi) is the only medication available for the treatment of cystinosis. It works by reducing the level of cystine in the cells.
According to a 2010 review, when administered early, cysteamine may:
- delay the development of kidney failure
- prevent or postpone delayed growth in infancy
- help prevent or delay other complications
Once starting the medication, your child will initially need a monthly blood test to make sure the dose is correct. Blood test frequency will be reduced to once every three to four months once a stable dosage is reached.
Cysteamine is also available as an eye drop formulation to prevent long-term damage to the eyes and to help improve pain and discomfort associated with bright lights.
Cysteamine is taken for life to help reduce the formation of cystine crystals.
To maintain kidney health, it’s important to drink plenty of water and fluids to replace those lost from frequent urination. Your doctor may also recommend vitamin D and phosphorus supplements to prevent rickets. Additional supplements may be needed to replace lost minerals, including:
Your doctor may also recommend a medication called an angiotensin converting enzyme inhibitor (ACE inhibitor) to reduce damage to the kidneys.
If you or your child develops kidney failure, your doctor will discuss the possibility of a kidney transplant with you. Cystinosis-related kidney damage doesn’t occur in the transplanted kidney. The new kidney allows the body to filter the blood effectively and typically resolves Fanconi syndrome.
Thyroid hormone replacement may be needed to treat hypothyroidism. Learn more about your treatment options for hypothyroidism.
Your pancreas produces hormones that help digest food, and it produces insulin. If your pancreas malfunctions, it can affect your insulin production and lead to diabetes. If you develop diabetes, you may need to take insulin to help manage your condition. Learn more about the connection between diabetes and your pancreas.
Growth hormone is sometimes given to children whose growth is affected. In children who have difficulty eating, doctors may suggest using a feeding tube to ensure they receive adequate nutrition.
Your doctor may recommend L-carnitine to help improve growth and muscle function.
There are several clinical trials currently recruiting participants with cystinosis. These include studies related to muscle wasting and a potential cure using stem cells.
Other trials include:
- a long-term study investigating cysteamine treatment
- a study collecting information on people with cystinosis to aid medical research
- a German trial looking at how a new blood test could be used to detect cystinosis
Talk to your doctor if you’re interested in participating in a clinical trial. They can help connect you with open trials or let you know when new trials are starting.
There’s also a patient registry designed to propel the development of future trials and connect researchers with potential study participants.
What is the outlook for people living
The treatment of cystinosis has improved over the past 30 years with the introduction of cysteamine and kidney replacement therapy.
A study conducted by the National Institutes of Health found that the average life expectancy of 100 study participants was 28.5 years. However, this study began in 1985, when the outlook and treatment for cystinosis were much different. Currently, there are adults living into their 50s with the condition, and there are new treatments on the horizon that may extend this further.
Earlier detection of cystinosis helps to delay, or prevent, the symptoms of the disease, but there’s still no definitive cure for cystinosis.