What are the genetic changes related to renal hypouricemia ?
Mutations in the SLC22A12 or SLC2A9 gene cause renal hypouricemia. These genes provide instructions for making proteins called urate transporter 1 (URAT1) and glucose transporter 9 (GLUT9), respectively. These proteins are found in the kidneys, specifically in structures called proximal tubules. These structures help to reabsorb needed nutrients, water, and other materials into the blood and excrete unneeded substances into the urine. Within the proximal tubules, both the URAT1 and GLUT9 proteins reabsorb uric acid into the bloodstream or release it into the urine, depending on the body's needs. Most uric acid that is filtered through the kidneys is reabsorbed into the bloodstream; about 10 percent is released into urine.  Mutations that cause renal hypouricemia lead to the production of URAT1 or GLUT9 protein with a reduced ability to reabsorb uric acid into the bloodstream. Instead, large amounts of uric acid are released in the urine. The specific cause of the signs and symptoms of renal hypouricemia is unclear. Researchers suspect that when additional uric acid is produced during exercise and passed through the kidneys, it could lead to tissue damage. Alternatively, without the antioxidant properties of uric acid, free radicals could cause tissue damage in the kidneys. Another possibility is that other substances are prevented from being reabsorbed along with uric acid; accumulation of these substances in the kidneys could cause tissue damage. It is likely that individuals with renal hypouricemia who have mild or no symptoms have enough protein function to reabsorb a sufficient amount of uric acid into the bloodstream to prevent severe kidney problems.