Does anyone know the difference between JAK positive and JAK Negative. Had second opinion from another haemo. Last week and was surprised to learn I have JAK 2 negative. He didn't really explain the difference only that I may need another BMB and I still have ET. Am to continue seeing usual haemo. for the time being. He said I'd get more information from forums than from any doctor! So all you experts out there can you shed any light on this please. Also have sore rib and he checked it and said it was fine. He also mentioned that he'd heard exercise helps which is something of a joke because walking is very difficult although I do try. Thanks people in anticipation.