Cystinosis

All you need to know about Cystinosis

  • January 14, 2022
  • 3 mins read

Globally, more than 2,000 people have cystinosis, which is a rare, multisystem genetic disease or disorder. Cystinosis is characterized by the accumulation of an amino acid known as cystine which forms crystals that have the potential to damage many organs and tissues, especially the eyes and kidneys. Although it can also be responsible for affecting the muscles, liver, pancreas and brain.

Generally, cystinosis is classified into three different forms known as:

  • Nephropathic cystinosis
  • Intermediate cystinosis
  • Non-nephropathic (or ocular) cystinosis

The age of onset, signs/symptoms, and the severity of cystinosis may vary broadly from one individual to another.

Who gets Cystinosis:

Cystinosis is a genetic/inherited disorder or disease that follows an autosomal recessive inheritance pattern, meaning that a copy of the defective gene, known as CTNS (Cystinosin, Lysosomal Cystine Transporter), must be passed down from both parents. Parents are the carrier of CTNS gene, but have no signs and symptoms. Their little one’s (children) have a 25% probability of being affected with cystinosis.

Symptoms of Cystinosis:

Cystinosis can be responsible for affecting several different parts of the body. The most commonly noted clinical findings, which start occurring during childhood, include:

  • Corneal cystine crystals
  • Excessive thirst dehydration
  • Hypothyroidism
  • Elevated cystine in white blood cells
  • Kidney disease
  • Excessive urination
  • Rickets
  • Slowed or halted growth

Note: The corneal crystals are a common clinical finding of cystinosis.

Causes of Cystinosis:

Cystinosis is caused by a mutation in the CTNS gene, most commonly 57-kb deletion. The CTNS (57-kb deletion) gene provides instructions for creating a transporter protein named cystinosin, which is basically responsible for moving the amino acid, cystine, out of the cell lysosome: the part of the cell that helps digest and recycles the materials. In case cystinosin turns defective or missing, cystine accumulates and forms crystals in the lysosomes, and starts damaging cells in the eyes, kidneys, and certain other organs.

How does cystinosis affect the eyes:

The corneal crystals may be present prior to age 12 months and are always present following the age 16. If corneal crystals is left untreated, it can lead to the following complications and potentially responsible for causing permanent damage to the eyes:

  • eye pain
  • excessive sensitivity to light
  • foreign body sensation in the eye
  • vision haziness
  • squinting
  • corneal abrasion
  • involuntary eye closure
  • band keratopathy (a complication where a line occurs across the cornea)

Treatment of Cystinosis:

Cystinosis treatment is focused on managing signs/symptoms. An oral treatment named cysteamine(cystagon) has been demonstrated to scale down the cystine level in the cells, improve growth in children, and stabilize the kidney and certain other functions. However, the treatment with oral cysteamine medicine does not lessen the ocular outcomes of the cystinosis since it does not influence the corneas.

The corneal crystals can be treated with Cysteamine Ophthalmic Solution (Cystagon/Procysbi/Cystaran 0.44% drops). Instill one drop of cysteamine ophthalmic solution in each eye, every waking hour. This medicine is the only FDA-approved ophthalmic treatment for corneal crystals in cystinosis patients.

Cysteamine Ophthalmic Solution Side Effects: The most commonly reported side effects (incidence around 10% or higher) are redness, headache, sensitivity to light, visual field defects, and eye pain/irritation..

Necessary Precautions: To keep down the contaminating the dropper tip and solution, care should be imposed not to touch the eyelids or other surrounding areas with the dropper tip of the bottle. The bottle should be kept very tightly closed when not in use.

Pseudotumor cerebri (benign intracranial hypertension) has been reported with oral cysteamine treatment that has resolved with the addition of diuretic therapy.

The Solution of Cysteamine Ophthalmic basically contains the benzalkonium chloride, which may be absorbed by the soft contact lenses. The contact lenses must be eliminated before the use of medicine and need to be reinserted fifteen minutes after its administration.

Reference Link:

https://rarediseases.org/rare-diseases/cystinosis/
https://cystinosis.org/about-cystinosis/cystinosis-101/