Crystals and stones
Children with Lesch-Nyhan disease make too much uric acid. When too much uric acid is made, it begins to stick together in clumps known as crystals. See the figure how they look under miscroscope. With the naked eye, pure uric acid crystals often look like yellow grains of sand. They may be as small as a poppy seed or as big as a lemon.
These crystals and stones like to form in three main areas of the body. The first area is the joints between bones, especially those of the toes or fingers. When this happens, the crystals cause irritation of the joints, a problem known as gout. Gout can be seen as a finger or toe that becomes swollen, red, and painful.
The second area that crystals and stones form is just under the skin in cool parts of the body. When they form here, they can be seen through the skin as tophi.
The last area crystals and stones form is in the kidneys. These are the most dangerous stones. Sometimes a stone will pass out of the kidney to show up in the urine, where it can actually be seen. Sometimes a stone will get stuck on its way to the bladder. This often causes pain in the belly, back, or upper leg. A trapped stone can also block the flow of urine. If a large stone gets stuck in the kidney or on its way to the bladder, it can prevent the kidney from doing its job and cause kidney failure.