How does polycythemia develop?
Before describing how polycythemia develops, we have to understand that this isn’t the only type of polycythemia and the term polycythemia means an increase in red blood cells. Polycythemia is classified into primary and secondary, with polycythemia vera referring to the primary type. Secondary polycythemia is a physiological response to inadequate oxygen delivery to cells of the body, prompting the body to respond by increasing the rate of production of red blood cells. This usually occurs in people living at high altitudes or smokers and those with some lung conditions like chronic obstructive pulmonary disease (COPD).
Primary polycythemia belongs to a group of diseases called myeloproliferative neoplasms (MPN). Other members of the group include chronic myeloid leukemia, essential thrombocythemia and myelofibrosis. The common mechanism of such diseases is that they develop due to a genetic defect called a mutation that affects the signal pathway which usually controls the rate of division of such cells leading to uncontrolled proliferation, thereby the suffix “proliferative”. This mutation has been found in a gene called Janus Kinase or JAK-2 gene in more than 95% of cases. The same mutation has been also found in essential thrombocythemia and myelofibrosis indicating the genetic constituent of all myeloproliferative neoplasms.
Cancers develop due to mutations, and those mutations have several risk factors. In general, exposure to radiation or chemotherapy as well as heredity can play a role, but generally speaking, they are more common in the older age group starting from the 6th decade for some cancers like colon cancer, and the 7th decade in the case of blood malignancies. The idea behind that is the long series of divisions that those cells underwent, with the risk of an uncorrected mutation increasing as the time passes. This is the same reason as to why elderly mothers and fathers tend to have children with a higher risk of genetic mutations like Down syndrome. The longer a machine operates, the greater the risk it will make mistakes.