Description, Causes and Risk Factors:
A lysosomal storage disorder with various forms, all with autosomal recessive inheritance. The nephropathic form of early childhood is characterized by widespread deposits of cystine crystals throughout the body, including the bone marrow, cornea, and other tissues, with mild elevation of plasma cystine and cystinuria; associated with a marked generalized aminoaciduria, glycosuria, polyuria, chronic acidosis, hypophosphatemia with vitamin D-resistant rickets, and often with hypokalemia; other extrarenal manifestations include photophobia and hypothyroidism; due to a defect in the transport of cystine across lysosomal membranes caused by mutation in the CTNS gene on 17p. There is a milder form with onset in adolescence and one with onset in adulthood without kidney damage; the latter two forms are thought to be allelic to the nephropathic form of early childhood.
Cystinosis is a condition in which the body accumulates the amino acid cystine (a building block of proteins) within cells. Excess cystine forms crystals that can build up and damage cells. These crystals negatively affect many systems in the body, especially the kidneys and eyes.
The disease affects approximately 1 in 100,000 to 200,000 newborns. The incidence is higher in the province of Brittany, France, where the disorder affects 1 in 26,000 individuals.
There are three clinical forms of cystinosis: Infantile (nephropathic); late-onset; and benign. Infantile cystinosis is the most severe and the most common type. Children with it appear normal at birth, but by 9-10 months of age have symptoms that include excessive thirst and urination and failure to thrive. Children often appear pale and thin and have short stature. The abnormally high loss of phosphorous in the urine leads to rickets.
Cystinosis is called a recessive genetic disease, because parents do not exhibit symptoms, but they each carry a recessive gene which may cause Cystinosis in their children. The genetic path of Cystinosis is therefore impossible to predict, and a cystinotic child is almost always a shock to parents. The recessive gene may lie dormant for many generation until suddenly two people with the defective gene have children.
Scientists have mapped the Cystinosis gene, CTNS, to chromosome 17p13. Researchers are creating mouse models of cystinosis that will lead them to better understand cystinosis and develop improved treatments for each complication.
Over the last 20 years, the prognosis of a child born with Cystinosis has greatly improved. However, now that people with cystinosis are surviving into their 20s, 30s, and 40s, new research questions need to be answered to give people with cystinosis an improved quality of life.
Symptoms may include:
- Excessive urination.
- Failure to thrive.
- Episodes of dehydration.
- Cystine crystals in cornea.
- Elevated cystine levels in white blood cells.
These symptoms usually appear between 6 and 18 months of age. They are caused by renal tubular Fanconi Syndrome, or a failure of the kidney
to reabsorb nutrients and minerals. The minerals are lost in the urine.
In late onset Cystinosis, kidney and eye symptoms typically become apparent during the teenage years or early adulthood.
In benign or adult Cystinosis, cystine accumulates primarily in the cornea of the eyes.
The presence of Cystinosis can be confirmed by determining the cystine content of peripheral blood leukocytes or fibroblasts. The assay using cystine binding protein is more sensitive and enables identification of heterozygous carriers. The intraleukocyte cystine content is 5-15 nmol of half-cystine/mg protein in the infantile form, 3-6 in the intermediate form, less than 1 in heterozygous carriers, and less than 0.2 in normal individuals.
The isolation and characterization of the suspect gene will eventually lead to the development of a genetic-based diagnostic assay. Although a polymerase chain reaction (PCR) based detection assay has been reported, such techniques are not routinely available at present.
Cystinosis is treated symptomatically. Renal tubular dysfunction requires a high intake of fluids and electrolytes to prevent excessive loss of water from the body (dehydration). Sodium bicarbonate, sodium citrate, and potassium citrate may be administered to maintain the normal electrolyte balance. Phosphates and vitamin D are also required to correct the impaired uptake of phosphate into the kidneys and to prevent rickets. Carnitine may help to replace muscular carnitine deficiency.
Cysteamine (Cystagon) has been approved by the FDA (Food and Drug Administration) for standard treatment of Cystinosis. Cysteamine is a cystine-depleting agents that lowers cystine levels within the cells. Cysteamine has proven effective in delaying or preventing renal failure. Cysteamine also improves growth of children with Cystinosis. In view of the harmful effects of chronic cystine accumulation, and the indications of the effectiveness of Cysteamine therapy in various tissues and organ systems, oral Cysteamine should be used by Post-transplant Cystinosis patients.
Cysteamine eye drops dissolve corneal cystine crystals and relieve photophobia.
NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.