Genetic disorders such as cystinosis cause the buildup of cystine within the cells, which is a building block of proteins. Cystinosis affects different organs and tissues in the body. Normally, cystine is transported out of the cells by a protein called cystinosin. Mutations in the gene responsible for cystinosin prevent this process in people with cystinosis. Therefore, cystine accumulates and forms crystals that damage cells and organs.
As an autosomal recessive disorder, cystinosis is inherited from the parents. To develop the condition, a person must inherit two copies of the mutated gene. Usually, the parents carry the mutated gene, meaning they have one normal copy and one mutated copy. Carriers do not experience symptoms of cystinosis, but they have a 25% chance of passing on the mutated gene.
Cystitis is caused by a gene called CTNS, which is found on chromosome 17 and encodes the protein cystinosin. Different types of mutations in CTNS can alter cystinosin's function. Cystitis can be classified into three main forms based on the type and severity of the mutation: nephropathic, intermediate, and non-nephropathic.
The symptoms of cystinosis vary depending on the form and the age of onset. Nephropathic cystinosis affects nearly 95% of people with the disease. It usually appears in childhood and causes kidney problems, growth failure, rickets, and eye damage. As the kidneys cannot absorb minerals and nutrients from the urine, they lose excessive amounts of water, salt, potassium, calcium, and phosphate. In addition to dehydration, electrolyte imbalance, acidosis, and poor growth, low levels of calcium and phosphate cause the bones to become soft and deformed, causing rickets. Cystine crystals accumulate in the cornea and cause light sensitivity, pain, and vision problems in the eyes.
A person with intermediate cystinosis may have similar symptoms to those with nephropathic cystinosis, but the symptoms may be less severe and progress more slowly. Intermediate cystinosis can also lead to kidney failure and the need for a kidney transplant.
Photophobia, eye irritation, and reduced visual acuity are all symptoms of non-nephropathic cystinosis, which usually appears in adulthood.
Cystinosis can also affect other organs and systems in the body, such as the brain, muscles, liver, thyroid, pancreas, and reproductive organs. Some of the possible complications include:
Neurological problems, such as seizures, headaches, stroke, and cognitive impairment.
Muscle weakness, wasting, and pain.
Liver enlargement, fibrosis, and cirrhosis.
Thyroid dysfunction, such as hypothyroidism or hyperthyroidism.
Diabetes mellitus, due to damage to the pancreas and insulin resistance.
Infertility, due to damage to the ovaries or testes.
The diagnosis of cystinosis is based on the clinical symptoms, family history, and laboratory tests. The main tests used to diagnose cystinosis are:
Measurement of cystine levels in white blood cells, using a technique called cystine-binding protein assay. This is the most reliable and specific test for cystinosis. It can detect the amount of cystine in the cells and differentiate between the different forms of the condition.
Genetic testing, using a blood sample or a cheek swab. This can identify the mutations in the CTNS gene and confirm the diagnosis of cystinosis. It can also be used for prenatal diagnosis and carrier testing.
Eye examination, using a slit-lamp microscope. This can reveal the presence of cystine crystals in the cornea and the iris of the eye.
The treatment of cystinosis aims to reduce the accumulation of cystine in the cells and prevent or delay the damage to the organs. The main treatments for cystinosis are:
The medication cysteamine reduces cystine levels in the cells by converting cystine into cysteine, which can be excreted from the body. It is taken orally as capsules or granules, or applied as eye drops. As well as slowing the progression of kidney disease, cystosis can also be treated or prevented with cysteamine, but it cannot reverse the damage caused by cystinosis. In addition to the above side effects, cysteamine can also cause bad breath, nausea, vomiting, diarrhea, stomach ulcers, skin rashes, and bone marrow suppression. Therefore, it is essential to follow the prescribed dosage and schedule, and to monitor the blood counts and liver function regularly.
In addition to electrolyte supplements, vitamin D, phosphate binders, growth hormone, thyroid hormone, insulin, and pain relievers, symptomatic treatments are also available. By correcting the imbalances and deficiencies caused by renal problems and other complications of cystinosis, these treatments can improve quality of life and prevent further complications from occurring.
Surgical procedures that replace damaged kidneys with healthy ones are known as kidney transplants. In addition to restoring kidney function, a kidney transplant eliminates the need for dialysis. However, it does not cure cystinosis or prevent damage to other organs. Therefore, people who receive a kidney transplant still need to take cysteamine and other medications for the rest of their lives. A kidney transplant has some risks, including infection, bleeding, and graft failure. Immunosuppressive drugs are also needed to prevent rejection of the transplanted kidney.
There is no way to prevent cystinosis, as it is a genetic disorder that is present from birth. However, some measures can help to reduce the risk of complications and improve the outcome of the condition. These include:
Early diagnosis and treatment, which can slow down the disease progression and preserve the organ function.
Regular follow-up and monitoring, which can detect and treat any problems or complications as soon as possible.
People with cystinosis and their families may benefit from genetic counseling and testing, which can provide them with information and guidance. It is possible to confirm the diagnosis, identify carriers, and offer prenatal diagnosis with genetic testing, which can provide insights into inheritance patterns, recurrence risks, and family planning options.
