Cystinosis

Cystinosis is a hereditary dysfunction of the renal tubules characterized by the presence of carbohydrates and amino acids in the urine, excessive urination, and low blood levels of potassium ions and phosphates. more...

Cause

It is caused by abnormal transport of the amino acid cystine from lysosomes of all tissues, resulting in a massive intra-lysosomal cystine accumulation. Via an as yet unknown mechanism, lysosomal cystine appears to amplify apoptosis such that cells die inappropriately, leading to loss of renal epithelial cells, accounting for the renal Fanconi syndrome, and simlar loss in other tissues can account for the short stature, retinopathy, and other features of the disease.

Symptoms

Symptoms include Fanconi Syndrome, photophobia, stunted growth and rickets. It is currently being researched at UC San Diego, Tulane University School of Medicine, and at the National Institutes of Health in Bethesda, Maryland.

Genetics

The cause of cystinosis is due to a mutation in the gene CTNS which codes for cystinosin, the lysosomal cystine transporter. Symptoms are seen about 6-18 months of age with profound polyuria ( excessive urination), followed by poor growth, photophobia, and ultimately kidney failure by age 10 years in the nephropathic form. It is importanat for the child to see a biochemical geneticist and pediatric nephrologist to begin cyteamine as early as possible. Cysteamine decreases the amount of cystine stored in lysosomes and correlates with conservation of renal function and improved growth. Cysteamine eyedrops remove the cystine crystals in the cornea that cause photophobia and may impair vision after age 20 years. All forms of cystinosis ( nephropathic, juvenile and ocular) are inherited as autosomal recessive traits, which means that there is a 25% recurrence risk to any couple who have had an affected child. The disease " breeds true" such that parents of a child with the juvenile variety of cystinosis will not have another child with the nephropathic form, etc.

Types

• OMIM 219800 - Infantile nephropathic
• OMIM 219900 - Adolescent nephropathic
• OMIM 219750 - Adult nonnephropathic

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