Cystinosis: A Rare Lysosomal Storage Disease

About Cystinosis:

Cystinosis affects approximately 2K individuals globally. It is a rare, genetic, metabolic, lysosomal storage disease that causes an abnormal accumulation of the amino acid cystine in different organs and tissues of the body such as the eye, kidneys, pancreas, muscles, and brain.

The cystine accumulation results in widespread tissue and organ damage. Cystine accumulation can be responsible for causing muscle wasting, kidney failure, diabetes, swallowing difficulty, hypothyroidism, blindness, cerebral atrophy, corneal ulceration, photophobia, ventilatory impairment, and more. Left untreated, children with cystinosis will usually develop end-stage kidney failure and die prematurely.

Early Signs and Symptoms of Cystinosis:

• Initial signs and symptoms are commonly due to cystine accumulation in the kidney tubules, which causes Fanconi syndrome. Left untreated, Fanconi syndrome will be responsible for end-stage renal disease, requiring a kidney transplant by age 10.
• Parents primarily notice frequent wet diapers (polyuria) and persistent thirst (polydipsia, resulting in dehydration) when first describing their child’s symptoms.
• Also commonly affected in the initial 6 to 18 months of life are the eyes, which can become photosensitive, and the bones, which can develop rickets. Damage to the thyroid further causes failure to thrive.

Clinical Forms and Symptoms of Cystinosis: There are 3 different forms of Cystinosis:

1. Infantile Nephropathic or Classic Cystinosis: Infantile Nephropathic is the most severe and prevalent form of Cystinosis (95 percent). Symptoms typically appear between 6 and 18 months.

• Excessive urination
• Failure to thrive
• Rickets
• Excessive thirst
• Episodes of dehydration
• Cystine crystals in the cornea
• Elevated cystine levels in WBCs

2. Intermediate, or Late-Onset Cystinosis: Late-Onset form has most features of the Infantile Cystinosis, but begins at a later age (adolescence). In this form, kidney and eye symptoms mainly become apparent during the teenage years or early adulthood. Identical to Infantile Nephropathic but with delayed onset and less severity.

3. Ocular Cystinosis: This form is characterized by crystal formation in the cornea and photophobia, without other manifestations of Cystinosis. In Ocular cystinosis, cystine accumulates mainly in the cornea of the eyes. No impaired kidney function or growth. The only symptom is Photophobia. Cystine crystals me be present in bone marrow as well as the cornea.

Note: The above listed symptoms are because of renal tubular Fanconi syndrome, or kidney failure to reabsorb minerals and nutrients. The minerals indulge in the urine.

Cystinosis Diagnosis:

Children typically display signs and symptoms by 9 months of age and can be diagnosed. Unfortunately, so many children are misdiagnosed and suffer for years or die before an appropriate diagnosis is done.

Diagnosis can be done by:

• Fanconi syndrome symptoms and documentation of urinary losses of glucose, vital electrolytes and minerals, and amino acids.
• A blood test that measures elevated white cell cystine levels
• An eye exam with a slit lamp in order to confirm crystals on the surface of the eye.

Treatment of Cystinosis:

Of the 3 forms of Cystinosis (Infantile Nephropathic, late-Onset & Ocular), this article is all about treating the most common and complex form named Infantile Nephropathic. Individuals with this rare disease are living longer, quality of life (QoL), because of enhanced awareness and better treatment options.

Cystinosis is a multi-system rare disease and treatment must be precisely coordinated with your health specialists. Persistent treatment from a tender age is critical.

• Cysteamine (Cystagon): Cysteamine (Cystagon 50 mg/150 mg) is a promising treatment for those with Cystinosis to scale down cystine accumulation in the cells. This drug has proven effective in order to delay or prevent renal failure. The medicine also helps increase the growth of children with cystinosis. This medicinal product may also be used in people with cystinosis after a kidney transplant for the prevention of the non-kidney complications of the disease. Under cysteamine therapy option, Cystagon is highly recommended medicine
• Cysteamine Eye Drops: Cysteamine eye drops are designed to dissolve corneal crystals and relieve photophobia in order to help prevent corneal ulcerations.

Reference:

https://rarediseases.info.nih.gov/diseases/6236/cystinosis

https://www.dpcedcenter.org/news-events/news/cystinosis-a-rare-and-under-recognized-cause-of-kidney-failure/