ALT is widely distributed in many tissues but is found in greatest abundance in the liver, and to a much lesser extent in the kidneys, heart, and brain. ALT has also been found to play an important role in neuronal function by supplying an important source of neuronal glutamate through the analine-aminotransferase reaction. Serum ALT levels are generally low, but may spike during disease states or in the event of tissue injury and are routinely used as indicators of medical issues, particularly liver diseases. Increased levels can be seen in patients with diabetes, cirrhosis, fatty liver disease, and hepatitis. Beyond liver disease, increased ALT levels have been noted in cases of carcinoma, mononucleosis, muscular dystrophy, and cardiovascular disease.