What is Cystinosis?
Cystinosis is a rare disorder of lysosomal storages. This condition occurs when a type of amino acid called cystine accumulates inside the lysosomes of body cells. High levels of cystine lead to cystine crystallization and can cause damage to vital organs, including the brain, liver, pancreas, eyes, and kidneys, and may lead to life-threatening complications.
What Are the Symptoms?
Cystinosis is a multisystem genetic disorder responsible for 5% of all listed cases of kidney failures in children. There are three types of cystinosis: non-nephropathic, intermediate, and nephropathic. They are classified based on the severity of the symptoms.
Both intermediate and nephropathic cystinosis share similar symptoms but differ at the age they start to manifest. The former appearing commonly during adolescence, and the latter appearing between 6 to 12 months of infancy. The symptoms include:
- Slow growth
- Frequent urination
- Frequent vomiting
- Fussiness and loss of appetite
- Photophobia or light-sensitive retinas
Another prominent symptom is the Fanconi syndrome, a disease affecting the kidney's ability to effectively absorb nutrients and minerals essential for bodily function.
Non-nephropathic, also called ocular cystinosis, is the mildest among the three, with photophobia as the main symptom. However, this type of cystinosis does not develop kidney malfunction and other symptoms related to the body's excretory function.
Cystinosis, a hereditary disease, is caused by a mutation of the cystonosin (CTNS) gene. The disorder is acquired when a child receives an abnormal cystonosin gene from each of their parents. CTNS provides the instruction for the creation of a protein cystonosin. Cystonosin is a protein responsible for transporting amino acid cystine, a by-product of lysosomal processes.
Lysosomes function as the digestive center and waste eliminator of cells. It works by breaking down substances such as protein, carbohydrates, and even dead cells. Failure of lysosomal function heavily affects the kidneys and other organs responsible for removing wastes and toxic substances.
Immediate identification and diagnosis of cystinosis are crucial in maximizing the therapeutic benefits of medications for the condition. Diagnosis for cystinosis is usually initiated upon identifying its prominent symptoms, a thorough clinical evaluation and patient history review, and a series of specialized tests. One such test is through measuring the cystine levels on polymorphonuclear leukocytes, a type of white blood cell.
A urinary examination may confirm the presence of renal Fanconi syndrome, a strong indicator of cystinosis. People will then be responsible for interpreting the examination results. They will check for excess loss of minerals, nutrients, electrolytes, amino acids, and carnitine.
An experienced ophthalmologist may confirm photophobia using a specialized microscope called a slit lamp. The presence of cystine crystals in the cornea verifies the diagnosis.
Molecular genetic testing can also confirm any abnormalities with the CTNS gene.
Doctors may perform prenatal tests to diagnose cystinosis when family history raises flags for the disorder's possible occurrence. Cystine levels can be measured by examining cells in the amniotic fluid during the fetal stage of pregnancy. Chorionic villus sampling of placental villi can also provide information on cystine levels during the prenatal phase.
Cystinosis is a progressive condition. Although the damage it can cause is irreversible, early detection and treatment initiation can help prevent or delay the onset of complications.
The treatment for cystinosis is targeted towards specific symptoms apparent in each individual. As cystinosis can progress and affect multiple organs, formulating a treatment plan may require collaboration between a team of health specialists. Some include, but are not limited to, kidney specialists, ophthalmologists, gastroenterologists, pediatricians, psychologists, and nutritionists.
Drug treatment for cystinosis primarily involves using FDA-approved oral cysteamine bitartrate, a cystine-depleting compound that greatly lowers cystine levels on a cellular level. Cystine-depleting therapy helps delay the progression of kidney complications due to cystinosis, as well as counteract the slow growth associated with the disease.
As the oral cysteamine does not effectively reach the eyes, cysteamine-infused eyedrops are used to lower cystine levels in the cornea.
Electrolytes and Fluids
In addressing Fanconi syndrome, the treatment plan also includes a high intake of fluids and electrolytes to prevent dehydration.
Cystinosis is progressive, and kidney failure and end-stage renal disease (ESRD) can only be delayed to a certain extent. Hence, the treatment plan may introduce the need for dialysis. Dialysis is a mechanical treatment process that filters waste products of the blood, simulating normal kidney function.
Alternatively, a kidney transplant is also an option. It is a surgical procedure that replaces a dysfunctional kidney with a healthy one, either from a live or deceased donor.
Kidney transplant patients may receive immunosuppressive therapies as a post-surgical intervention. In some cases, treatments to address diabetes and hypothyroidism may be needed as a part of the recuperation plan.
Most interventions for cystinosis include counseling for both the patient and their families. Speech and language therapy may prove to be beneficial in some cases.