SNP Shot: Genomic Insights

Cystinosis is a disorder where the amino acid cystine accumulates inside cells. This buildup of cystine damages cells and can form crystals, leading to complications in various organs and tissues. The kidneys and eyes are particularly susceptible, but muscles, the thyroid, pancreas, and testes can also be affected.

There are three different types of cystinosis, categorized by their severity: nephropathic cystinosis (the most severe), intermediate cystinosis, and non-nephropathic or ocular cystinosis (the least severe).

Nephropathic cystinosis, which appears in infancy, causes poor growth and a specific type of kidney problem called renal Fanconi syndrome. In this syndrome, substances that should be reabsorbed into the body are lost in the urine. This loss results in a deficiency of vital minerals, salts, fluids, and other nutrients, hindering growth and potentially leading to soft, bowed bones (hypophosphatemic rickets), particularly in the legs. These imbalances cause increased urination, excessive thirst, dehydration, and abnormally acidic blood (acidosis). Around age 2, cystine crystals may appear in the cornea (the clear front part of the eye), causing pain and heightened sensitivity to light (photophobia). Without treatment, kidney failure occurs by about age 10. Other potential problems in untreated individuals, especially after adolescence, include muscle weakening, blindness, difficulty swallowing, diabetes, thyroid and nervous system issues, and infertility in men.

Intermediate cystinosis presents with similar symptoms to nephropathic cystinosis, but the onset is later, typically during adolescence. The primary initial features are kidney dysfunction and corneal crystals. Untreated intermediate cystinosis also leads to kidney failure, usually in the late teens or early twenties.

Individuals with non-nephropathic or ocular cystinosis primarily experience photophobia due to cystine crystals in the cornea. They generally do not develop kidney problems or most of the other severe symptoms associated with cystinosis. The age of diagnosis for this form varies widely due to the milder symptoms.

Inheritance:

Cystinosis is an autosomal recessive genetic disorder. This means that a person must inherit two copies of the mutated gene, one from each parent, to develop the condition. The parents are carriers, meaning they each have one copy of the mutated gene but usually don't show any symptoms of the disorder.