Also known as Myeloproliferative Leukaemia Gene (MPL), Thrombopoietin Gene (MPL) Mutation Detection; MPL W515L, MPL W515K Mutation. The MPL mutation test is used, along with other genetic testing to help diagnose bone marrow disorders that involve the overproduction of blood cells. These conditions are known as myeloproliferative neoplasms (MPNs).

The MPL gene provides the instructions for making a protein that controls the production of blood cells, especially platelets, which are made in the bone marrow. Mutations to the MPL gene can cause the receptor protein to be constantly switched on which leads to uncontrolled production of blood cells.

Your doctor may request an MPL mutation test if they suspect you may have a myeloproliferative neoplasm (MPN). The MPNs most commonly associated with MPL mutation are:

• Polycythaemia vera (PV) – too many red blood cells. 
• Essential thrombocythaemia (ET) –too many platelets.
• Primary myelofibrosis (PMF) also known as chronic idiopathic myelofibrosis or agnogenic myeloid metaplasia –too many platelets and cells that produce scar tissue in the bone marrow. 

Typically, the MPL mutation test would be ordered if you have already had routine laboratory tests such as a full blood count (FBC) that have revealed abnormal results known to be associated with these MPNs.  These include a significantly increased haemoglobin and/or platelet count. You would also have signs and symptoms that suggest an MPN such as  fatigue, fevers, weight loss, bone pain, and night sweats.

There are other gene mutations, also known as variants, that are associated with MPNs. The Janus Kinase 2 (JAK2) gene, and the calreticulin gene (CAL-R) have been associated with ET and PMF. BCR-ABL genetic testing is also sometimes used to check for the presence or absence of a Philadelphia (Ph') chromosome or a BCR-ABL translocation in someone suspected of having chronic myelogenous leukaemia.

These changes are acquired mutations known as somatic mutations and not inherited mutations, which are known as germline mutations.   

Sample 
Blood or bone marrow  

Any preparation?
None

The primary MPL tests are MPL W515L, or MPL W515K, named for mutations at a specific locations in the MPL gene.

If the MPL W515L or W515K mutation is detected and you have other supporting clinical signs, it is likely you have an MPN. Other testing, such as a bone marrow biopsy, may be needed to determine which MPN you have and to evaluate its severity.

If you are negative for MPL mutations, you may still have an MPN. You could have mutations in other genes such as JAK2.  Mutation testing for both MPL and JAK2 are often ordered at the same time since both lead to the same symptoms.

MPL mutation testing is carried out by a laboratory that performs molecular testing. It is not offered by every laboratory and must often be sent to a reference laboratory.

MPL mutation testing is rebated by Medicare. A specialist doctor may order JAK2 and/or MPL mutation testing in the workup of suspected polycythaemia vera or essential thrombocythaemia.