Fatty Liver Disease: This is the most common cause of mildly elevated ALT with normal AST. Fatty liver disease, particularly non-alcoholic fatty liver disease (NAFLD), often presents with isolated ALT elevation due to the accumulation of fat in liver cells.

Viral Hepatitis: Acute or chronic viral hepatitis (e.g., hepatitis B or C) can cause elevations in liver enzymes, including ALT. The pattern of elevation can vary, but ALT is often more elevated than AST in the early stages.
Alcoholic Liver Disease: While AST is typically more elevated than ALT in alcoholic liver disease, early stages or mild cases might present with a mild elevation in ALT and a normal AST.
Medication-Induced Liver Injury: Certain medications can cause liver enzyme elevations. The pattern can vary depending on the medication, but some may present with isolated ALT elevations.

Wilson's Disease: A genetic disorder leading to copper accumulation in the liver. It can present with liver enzyme elevations, including ALT, and is critical to diagnose early to prevent liver damage.
Autoimmune Hepatitis: An autoimmune condition causing liver inflammation. It can present with elevated liver enzymes, including ALT, and requires prompt treatment to prevent severe liver damage.
Alpha-1 Antitrypsin Deficiency: A genetic disorder that can lead to liver disease. It's essential to consider in individuals with unexplained liver enzyme elevations, as it requires specific management.

Hemochromatosis: A genetic disorder causing iron overload, which can lead to liver damage and enzyme elevations. It's less common but important to consider in the differential diagnosis.
Glycogen Storage Diseases: Rare genetic disorders affecting glycogen metabolism, which can lead to liver enzyme elevations, including ALT.
Budd-Chiari Syndrome: A rare condition caused by hepatic vein thrombosis, leading to liver congestion and potential enzyme elevations. It's a critical diagnosis to consider due to its severe consequences if not treated promptly.