Which are the causes of Cystinuria?

Cystinuria is a rare genetic disorder characterized by the abnormal transport of the amino acid cystine in the kidneys and urinary tract. This condition leads to the formation of cystine stones, which can cause significant pain and complications. While the exact cause of cystinuria is not fully understood, it is believed to be primarily caused by genetic mutations that affect the transport of cystine.

Genetic Mutations: Cystinuria is an inherited disorder, which means it is passed down from parents to their children through genetic mutations. The responsible genes for cystinuria are SLC3A1 and SLC7A9, which encode proteins involved in the transport of cystine in the kidneys. Mutations in these genes can disrupt the normal function of the transporters, leading to the accumulation of cystine in the urine and subsequent stone formation.

Autosomal Recessive Inheritance: Cystinuria follows an autosomal recessive pattern of inheritance, meaning that an individual must inherit two copies of the mutated gene (one from each parent) to develop the disorder. If both parents are carriers of the cystinuria gene, there is a 25% chance with each pregnancy that their child will inherit two copies of the mutated gene and develop cystinuria.

High Cystine Concentration: The abnormal transport of cystine in individuals with cystinuria leads to a higher concentration of cystine in the urine. Cystine is a naturally occurring amino acid that is normally reabsorbed by the kidneys and returned to the bloodstream. However, in cystinuria, the defective transporters prevent efficient reabsorption, resulting in the accumulation of cystine and its subsequent precipitation as crystals. Over time, these crystals can grow and form stones in the kidneys or urinary tract.

Dietary Factors: While genetic mutations are the primary cause of cystinuria, certain dietary factors can exacerbate the condition. A diet high in certain amino acids, such as cysteine, methionine, and lysine, can increase the concentration of cystine in the urine, making stone formation more likely. Additionally, inadequate fluid intake can contribute to the formation of cystine stones by reducing urine volume and concentration, allowing cystine to crystallize and form stones more easily.

Other Factors: In some cases, certain medications or medical conditions can increase the risk of cystine stone formation in individuals with cystinuria. For example, medications that alkalinize the urine or decrease urine volume can promote cystine precipitation. Additionally, urinary tract infections or other conditions that cause urinary stasis can contribute to stone formation.

In conclusion, cystinuria is primarily caused by genetic mutations that affect the transport of cystine in the kidneys. These mutations disrupt the normal reabsorption of cystine, leading to its accumulation in the urine and the formation of cystine stones. While dietary factors and other medical conditions can contribute to stone formation, genetic mutations and the resulting abnormal cystine transport are the underlying causes of cystinuria.