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Understanding Cystinosis: Shedding Light on a Rare Genetic Disorder

Jan 11, 2024

Cystinosis is an inherited disorder that causes an abnormal buildup of cystine (an amino acid) in the body. This rare disease typically presents in infants and children when they are young.
There is currently no cure for this rare disease. However, there are available treatments that can improve life expectancy.

Key Points

  • Cystinosis is a rare genetic disorder that is characterized by the buildup of cystine in different organs and tissues of the body.
  • Commonly affected organs include the eyes, kidneys, pancreas, muscles, liver, and brain.
  • Early detection and appropriate treatment are essential in slowing the development and disease progression of symptoms associated with cystinosis.

What is Cystinosis?

It is estimated that fewer than 5,000 people in the U.S. have cystinosis. It is a genetic condition that can present at birth and results in the buildup of cystine crystals in the body. Cystinosis is classified as a disorder of lysosomal storage.

Lysosomes are the primary digestive unit in cells and break down nutrients such as proteins, fats, and carbohydrates. Some enzymes that occur within lysosomes break down these nutrients, while other proteins are responsible for transporting leftover metabolic products, such as cystine, out of the lysosome.

In cystinosis, there is no specific transporter, which causes cystine to build up in the lysosomes of the body’s cells. Cystine forms crystals in many cells, damaging the tissues and organs in the body. Cystinosis more frequently affects the eyes and the kidneys.

The accumulation of cystine may lead to muscle wasting, kidney failure, diabetes, photophobia, blindness, swallowing difficulty, and more.

Signs and Symptoms of Cystinosis

The severity of cystinosis and specific symptoms vary significantly from one person to another based upon factors such as age of onset and when the disorder was diagnosed and treated.
There are three distinct types of cystinosis that differ in the severity of symptoms and age of onset. They are:

Infantile (early-onset) nephropathic cystinosis

This is the most frequent and severe type of cystinosis. The symptoms of this form of cystinosis generally become apparent between 6 and 12 months of age. Symptoms may be severe or mild, but this is dependent on when treatment started and each individual case.

Signs and symptoms include the following:

  • Growth failure or stunted growth
  • Fanconi syndrome (characterized by kidney dysfunction, where the kidneys stop reabsorbing minerals and nutrients.)
  • Rickets (from nutritional loss and stunted growth)
  • Episodes of poor appetite, feeding difficulties, and vomiting
  • Nutritional deficiencies
  • Muscle spasms
  • Bone abnormalities
  • Abnormalities in the muscles, intestine, brain, liver, eyes, and other parts of the body
  • Learning difficulties
  • Reduced secretion of tears, sweat, and saliva
  • Electrolyte imbalance
  • Polyuria or increased production of dilute urine
  • Dehydration

If left untreated, nephropathic cystinosis may cause kidney failure by the age of 10 years old.

Intermediate cystinosis

It is also called nephropathic juvenile cystinosis or adolescent cystinosis. The average age that intermediate cystinosis presents is about eight years of age. This form of the disorder progresses slowly. Symptoms of intermediate cystinosis are similar to those of nephropathic cystinosis except those symptoms present in adolescence.

Major symptoms include:

  • Kidney dysfunction, which may lead to kidney failure (more common in late teens or early 20s)
  • Ocular discomfort (increased sensitivity to light and eye discomfort)

Other signs and symptoms may include:

  • Delayed puberty
  • Muscle abnormalities resulting in difficulty breathing or swallowing
  • Reduced secretion of testosterone
  • Blindness

Symptoms of adolescent cystinosis are generally less severe than infantile nephropathic cystinosis. However, if left untreated, end-stage renal failure develops typically between the ages of 15 and 25 years of age.

Non-nephropathic (adult-onset) cystinosis

Individuals with non-nephropathic or ocular cystinosis will mainly experience problems with their eyes (photophobia). Those with this form of cystinosis typically will not have kidney disease. If left untreated, photophobia will result due to the accumulation of cystine crystals in the eyes.

Knowing when symptoms present can help healthcare providers determine the correct diagnosis. Not everyone will have all the symptoms mentioned above. Patients with cystinosis and parents of affected children should discuss with their healthcare provider and medical team about their specific case, overall prognosis, and associated symptoms.

Causes of Cystinosis

Cystinosis is an inherited autosomal recessive disorder, meaning that it is passed down through families. For the disorder to appear, someone needs two faulty copies of the CTNS gene.

When the CTNS gene is defective, cystinosin becomes impaired, causing a cystine buildup within the lysosomes. All types of cystinosis are caused by a genetic mutation of the CTNS (cystinosis) gene.

Cystinosis Diagnosis

Different methods, such as a physical exam, medical history, and a genetic test, are used to diagnose cystinosis. For example, the eyes will be examined to check if there are cystine crystals present in the corneas. Physical signs of eye problems begin to present after two years of age. A genetic test may also be used to help confirm cystinosis by looking for genetic mutations in the CTNS gene.

A major test for cystinosis is measuring the amount of cystine in the white blood cells. Two tests (blood and urine) can be used to determine how well the kidneys are functioning. Radiology tests may be used to determine how well the other organs are working.

Healthcare providers can use prenatal tests such as amniocentesis or chronic villus sampling to test for cystinosis in a baby.

Cystinosis Treatment

As there is not yet a cure for cystinosis, treatment focuses on reducing and managing symptoms. This requires a team of specialists, such as pediatricians, nephrologists, psychologists, ophthalmologists, and gastroenterologists. Treatment options for cystinosis may include:

Cystine depleting therapy

The only target-specific treatment for cystinosis patients is aminothiol cysteamine (beta-mercaptoethylamine). This treatment aims to empty lysosomal cystine in all the cells and tissues in the body.

Symptomatic therapy

Symptomatic therapy is supportive and aims to:

  1. Maintain an appropriate fluid-electrolyte substitution and protect the acid-base balance
  2. Provide nutritional support
  3. Prevent the development of rickets
  4. Ensure that there is the proper substitution of required hormones (growth hormone therapy)

Other therapies, such as speech and language, may be beneficial for patients. Some patients and families may need genetic counseling.

Renal transplantation

Despite early and appropriate treatment, some patients with infantile and intermediate cystinosis develop ESRD and need a kidney transplant. Before undergoing a kidney transplant, the patient may undergo dialysis.

While patients with cystinosis typically respond well to a kidney transplant, cystine can still build up in other organs and tissues of the body.

Therapeutic Monitoring

Currently, the gold standard in therapeutic monitoring of patients with cystinosis is the WBC cystine assay.

Cystinosis Life Expectancy

With an early diagnosis and appropriate treatment, the life expectancy of someone with cystinosis is approximately 50 years. Many cystinosis patients live into middle age.

Clinical Trials

There is no known cure for cystinosis. However, there are, for example, new drugs and advancements in stem cell research that have helped improve survival rates. Talk to your healthcare provider or medical team about participating in clinical studies.

ClinicalTrails.gov can be used to search for any additional clinical studies. If there are no available clinical studies, ResearchMatch specializes in helping connect those interested in research studies with researchers from leading medical centers across the U.S.

Panoramic Health

Panoramic Health is the United States leading kidney care provider group. We provide unparalleled integrated operational capabilities that help deliver better patient outcomes and lower costs for everyone involved.