GAIS, or Glycogen Storage Disease Type II, is a rare genetic disorder that affects the body's ability to break down glycogen, a stored form of glucose. This condition is caused by a deficiency in the enzyme acid alpha-glucosidase, which is essential for converting glycogen into glucose. As a result, glycogen accumulates in various tissues, particularly in the muscles, leading to muscle weakness and other health issues. Symptoms of GAIS can vary widely but often include progressive muscle weakness, respiratory problems, and heart issues. Diagnosis typically involves genetic testing and enzyme activity assays. Treatment options may include enzyme replacement therapy and supportive care to manage symptoms and improve quality of life.