The CALR mutation refers to changes in the CALR gene, which provides instructions for making a protein involved in blood cell production. This mutation is commonly associated with certain blood disorders, particularly myeloproliferative neoplasms (MPNs), where the bone marrow produces too many blood cells. Individuals with a CALR mutation often experience symptoms like fatigue, headaches, and an increased risk of blood clots. Testing for this mutation can help diagnose conditions such as essential thrombocythemia and primary myelofibrosis, guiding treatment options for affected patients.