|MadSci Network: Genetics|
Hi Amy, There's a really good reason why you couldn't find anything on Cystinosis -- in the United States only 400 people are affected, making it one of the most rare genetic diseases out there! It is inherited in an autosomal recessive pattern, and the gene responsible is found on chromosome 17. Cystinosis is actually more commonly known as one of the causes of Renal Fanconi Syndrome, which is a collection of symptoms involving impaired kidney function including polyuria (excessive urination), polydipsia (excessive thirst), and hypokalemia (abnormally low levels of potassium in the blood). Individuals with Cystinosis also suffer from retarded growth and poor appetite, as well as abnormal sensitivity to light and loss of color in the retina of the eyes. The specific defect associated with Cystinosis is a mutation in the gene that codes for the lysosomal cystine transporter. Cystine is an amino acid found in many proteins. Lysosomes, which are membrane bound particles within cells, aid in intracellular digestive function. Cystinosis is characterized by the accumulation of cystine in the lysosomes of tissues throughout the body, which can cause certain organs, the kidneys in particular, to malfunction. If left untreated, the disease may lead to kidney failure by 10 years of age. The eye problems associated with Cystinosis are caused by crystallization of cystine in the cornea of the eyes. Three forms of Cystinosis are recognized. Infantile Nephropathic Cystinosis is the most severe form of the disease, and symptoms appear as early as 6 to 12 months after birth. In people with Intermediate Cystinosis or Juvenile (Adolescent) Cystinosis, kidney and eye symptoms typically become apparent during the teenage years or early adulthood. A form of the disease known as Benign or Adult Cystinosis is associated more with corneal problems than with kidney malfunction. Treatments of the disease are really quite diverse. To combat the excessive loss of salts in urine, electrolyte replacement therapy is given (sodium and potassium salts). Patients also drink large amounts of water to prevent dehydration. A more direct therapy is to treat with aminothiols (specifically a drug called Cystagon), which deplete the lysosomes of cystine. Cystinosis patients can also become hypothyroid (their thyroid glands are not active enough) so they are given hormone replacement therapy. Because children with cystinosis are often very much shorter than other children their age, they are also commonly placed on growth hormone therapy as well. So you now know a lot more than most people do about this disease; even most of the doctors I know had no idea what cystinosis is. That was a great question -- keep them coming! :)Carolyn
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