What is Cystinosis?
It is a metabolic disorder manifested by deposition of amino acid cystine in the body. In this condition, cystine accumulates in the lysosomes, and hence it is called a lysosomal storage disorder.
Classification of this condition is solely based on the initial signs and symptoms. Mentioned below are the various types of the disorder:
- Nephropathic cystinosis
- Intermediate cystinosis
- Non-Nephropathic/Ocular cystinosis
Renal problems are common in nephropathic cystinosis-affected patients. There is a severe deficiency of minerals like fluids, salts and nutrients due to poor kidney growth as well as associated disorders, including Fanconi syndrome. Many young children suffer from rickets that causes bowed legs and other bone deformities. Constant mineral loss gives rise to dehydration, thirst, acidosis and frequent urination. Abnormal intolerance to light is a result of constant deposition of crystine crystals in the cornea. These crystal deposits can also be present in kidneys of young children. In addition to these conditions, affected patients suffer from the following problems:
- Neurological deficits
- Thyroid impairment
- Difficulty swallowing
- Visual loss
- Pigment loss in skin and hair
The disorder normally follows an autosomal recessive pattern in which both copies of a gene undergo mutation. The causative gene CTNS, located on chromosome 17, is usually responsible for producing a lysosomal cystine transporter called cystinosin. The lysosomes become incapable of transporting cystine, causing excessive accumulation of the amino acid in the tissues. The renal tissues undergo apoptosis when these cystine crystals begin to accumulate in the kidney. Individuals who carry two copies of the defective gene are more likely to suffer from the disorder.
Clinicians usually examine the serum electrolyte and blood gases levels to detect the presence of acidosis. As the condition leads to increased renal excretion of amino acids, potassium, phosphate, and glucose, a simple urine test can reveal abnormalities in the kidney. Corneal cystine crystals can easily be identified with the aid of slit-lamp examination. Ultrasonography of the kidneys, ureters, and bladder can assess urinary tract calcifications. Nephropathic cystinosis can be detected by magnetic resonance imaging and computed tomography scanning.
Administration of cysteamine can clear large amounts of intracellular cystine. This particular drug permeates into the lysosomes to react with cystine and form cysteine as well as cysteine-cysteamine complex. The symptoms begin to gradually reduce as the lysosomal cystine shows a sharp decrease. Corneal cystine crystals can be removed using cysteamine eye drops. Acidosis-affected patients are often administered with sodium citrate and supplements of phosphorus as well as potassium. In case of a kidney failure, healthcare providers may opt for renal transplantation.
Cystinosis Life Expectancy
Cystinosis is a life-threatening disorder and has a low life expectancy. However, timely treatment can prevent unnecessary accumulation of the amino acid in the body.
Cystinosis Research Foundation
A host of medical investigators are currently carrying out research in the following institutions:
- University of Michigan
- University of California San Diego
- Tulane University School of Medicine
- National Institutes of Health in Bethesda
- Robert Gordon University in Aberdeen, Scotland
- Necker Hospital, Paris
- University of Sunderland, UK
There are some non-profit organizations like Cystinosis Research Network that provide support and proper information to the patients as well as their family members.