Cystinosis is a relatively rare genetic condition, with an estimated 15 new cases diagnosed in the United States each year. Cystinosis is an inborn error of metabolism that leads to the abnormal accumulation of the amino acid cystine in the lysosomes of cells. Also called cystine storage disease, crystals of cystine start to build up in various tissues and organs throughout the body.
There are three distinct forms of the condition which include nephropathic cystinosis, non-nephropathic cystinosis and intermediate cystinosis. The most severe, nephrophatic form of the disease begins in infancy and is characterized by particularly high levels of cystine inside the cells, especially white blood cells and fibroblasts.
Tandem mass spectrometry is usually used to measure white blood cell cystine levels and confirm a diagnosis. The cystine crystals that deposit in the kidneys eventually cause Fanconi syndrome which describes the defective reabsorption of amino acids, salts, sugar and water in the kidneys. Blood tests can therefore be run to check the levels of these substances in the blood. The urine level of cystine can also be checked.
A much less severe form of the condition called non-nephropathic cystinosis mainly only affects the eyes. The accumulation of cystine crystals in the cornea can cause photophobia which is a visual hypersensitivity to light. An ophthalmologist may therefore examine the eyes for evidence of cystinosis in the cornea and retina.
Prenatal diagnostic testing is available for families known to be at risk of giving birth to a child that will be affected by cystinosis. Chorionic villus sampling may be performed at around 8 or 9 weeks of gestation and amniocentesis at around 14 to 16 weeks of gestation.
Diagnosing cystinosis and starting treatment as early on as possible can help to prolong lifespan in people with the condition.
Reviewed by Sally Robertson, BSc