With early diagnosis and proper treatment, the life expectancy of someone with cystinosis is about 50 years. Many patients survive into middle age.
Although there is no cure for cystinosis, new drugs and advancements in stem cell research have helped improve cystinosis survival rates. Because the disease is rare, regular medical screenings to monitor the condition is advised.
What is cystinosis?
Cystinosis, also known as cysteine storage disease, is a rare hereditary condition that affects 1 out of every 100,000 to 200,000 live births in the United States.
Cystinosis is an inherited metabolic defect that results in an abnormal accumulation of the amino acid cysteine in cell lysosomes. Excess cysteine can lead to the formation of crystals, which can impact the kidneys, eyes, liver, thyroid, muscles, pancreas, brain, and white blood cells. If left untreated, some types of cystinosis can progress to renal failure.
What are different types of cystinosis?
Nephropathic cystinosis manifests itself in childhood and progresses rapidly. It is the most severe type.
Symptoms include development issues and Fanconi syndrome, which stops the kidneys from reabsorbing nutrients and minerals. This nutritional loss stunts growth and can lead to rickets. Cystine crystals can accumulate in the corneas of the eyes, leading to discomfort and increased sensitivity to light. They can cause muscular pain, vision problems, and infertility, thyroid, and neurological system issues.
If left untreated, the condition can cause full kidney failure by the age of 10 years.
Possible symptoms of nephrotic cystinosis include:
- Growth failure
- Kidney dysfunction
- Polyuria or increased production of dilute urine
- Nutritional deficiencies
- Electrolyte imbalance
- Feeding difficulties
- Poor appetite
- Reduced secretion of sweat, saliva, and tears
- Collapse due to heat exhaustion and dehydration
- Acidic blood
- Hypophosphatemic rickets (very low levels of phosphate in blood)
- Bone abnormalities
- Muscle spasms
- Abnormal gait
- Difficulty walking
- Abnormalities in the muscles, eyes, intestine, liver, brain, genitals, and other body parts
- Sensitivity to light
- Learning difficulties
- Difficulty with depth perception
- Difficulty identifying objects by touch
- Psychological and social problems
2. Intermediate cystinosis or nephropathic juvenile cystinosis
The average age of onset of intermediate cystinosis is about 8 years. The condition progresses slowly.
Symptoms are similar to those of nephropathic cystinosis, except they appear in adolescence. Major symptoms include kidney difficulties and ocular discomfort and sensitivity. Kidney failure can occur, but it is more common in the late teens or early 20s.
Symptoms of intermediate cystinosis include:
- Reduced secretion of testosterone
- Delayed puberty
- Muscle abnormalities, leading to difficulty swallowing and breathing
3. Non-nephropathic or ocular cystinosis
The age of onset of non-nephropathic cystinosis varies. However, it is usually noticed around middle age.
The most prevalent symptom of non-nephropathic (ocular) cystinosis is an accumulation of crystals in the corneas of the eyes, causing discomfort and photosensitivity (increased sensitivity to light).
Non-nephropathic cystinosis does not generally cause kidney difficulties or any of the other symptoms associated with cystinosis.
What causes cystinosis?
Cystinosis is a hereditary condition caused by a mutation(s) in the CTNS gene. When the gene is defective, cystinosin becomes dysfunctional, resulting in cystine buildup within the lysosomes. Therefore, family history of the condition is a key risk factor for developing the disorder.This condition is inherited autosomal recessively. This means that for the syndrome to appear, a person must have two faulty copies of the CTNS gene.
How is cystinosis diagnosed?
Cystinosis is suspected in children who have developmental delays and fail to grow at a normal pace. Tests that may confirm a diagnosis of cystinosis may include:
How is cystinosis treated?
Treatment of cystinosis focuses on reducing symptoms and may involve a team of specialists including:
Treatment options for cystinosis include:
Cystine depleting therapy
Cysteamine is a cystine-depleting chemical that may significantly reduce cystine levels within the cells. Cysteamine therapy reduces the onset and progression of kidney disease and improves growth in children. Cysteamine can greatly postpone the need for a kidney transplant.
Cysteamine therapy should begin as soon as possible following diagnosis to avoid or reduce renal impairment. Studies have reported that long-term cysteamine therapy can prevent many of the nonrenal, late-onset consequences of cystinosis.
Cysteamine is accessible in various forms, including ophthalmic solution. Cysteamine may be given along with proton pump inhibitors to prevent acid-related complications.
Side effects of cystine depleting therapy include:
Symptomatic therapy involves high intake of fluids and electrolytes to prevent dehydration. Sodium bicarbonate, sodium citrate, magnesium, and potassium may be administered to help maintain normal electrolyte balance. Medications may include:
- Angiotensin-converting enzyme inhibitors to slow the progression of renal disease.
- Anti-inflammatory medications such as indomethacin to reduce urinary loss of water and electrolytes and improve growth rate.
- Phosphates and vitamin D to correct impaired reabsorption of phosphate into the blood and prevent rickets.
- Carnitine for some pretransplant individuals to improve muscle strength.
- Growth hormone therapy to improve growth.
- L-thyroxine to treat hypothyroidism
- Insulin to treat insulin-dependent diabetes
- Testosterone to treat men with hypogonadism (underactive testicular function) so that secondary sexual characteristics will develop
Other treatment for cystinosis may include:
- Proper nutrition
- Avoidance of bright light
- Implantation of a gastronomy tube for dysphagia, poor nutrition, and increased risk of aspiration.
- Speech and language therapy
- Genetic counseling
Growth hormone therapy
Treatment with recombinant human growth hormone accelerates growth. Long-term recombinant human growth hormone treatment prior to renal replacement therapy in young children with nephropathic cystinosis has proven to be safe and effective.
Individuals with cystinosis often react extremely well to kidney transplantation, which can cure renal Fanconi syndrome because cystine does not build in the transplanted kidney.
What are possible complications of untreated cystinosis?
Possible complications of untreated cystinosis include:
- Kidney failure and ESRD
- Short stature
- Increased secretion of stomach acids
- Severe muscle wasting
- Difficulty swallowing and breathing
- Continued accumulation of cystine crystals in internal organs, leading to an enlarged liver and spleen
- High blood pressure
- Eye pain due to spasm of the eye muscles
- Reduced night and/or color vision
- Loss of visual acuity
- Reduced brain function
- Hearing loss
- Kidney stones
Cystinosis: the evolution of a treatable disease: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3505515/
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