As mentioned above, genetics. There are several disorders that can cause polycythemia. One of them is Janus Kinase 2 (JAK2) mutation.
There are numerous hereditary disorders. Same for clotting problems. There is a mutation of the clotting cascade that falls under the Leiden factor V (Factor 5) classification. It can cause thrombophilia.
There are 3 loves in my life: my wife, my English mastiffs, and my weightlifting....Man, my wife gets really pissed when I get the 3 confused...
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