Test Details: The calreticulin (CALR) gene is responsible for making a protein called calreticulin which is involved in functions such as ensuring the correct folding of new proteins, maintaining correct calcium levels in cells etc. Mutations of the CALR gene are associated with bone marrow neoplasms that cause the production of excessive blood cells. They are present in about 20-25% of adults with Essential thrombocythemia (ET) and 25-30% of adults with Primary Myelofibrosis (PMF).