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ET - JAK 2 negative

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.

6 Replies

JAK2 negative just means that the test has shown you don't have that gene mutation. Next thing would be to check if you have the CALR mutation, as that's the next most common one - though some people test negative for both.

I'm CALR+ and while it doesn't change the basics of having ET I found it helpful to know what is causing my ET, even if they don't know what causes the genetic mutation itself..!

As treatments develop in the future, it may be more relevant to know which mutation you have as there may be different treatments for each.

Hope that helps a bit!


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Hi, I'm jak2 negative and have Polycythaemia. I was told that another gene mutation would have caused my problem but it wasn't worth testing because the treatment would be the same - perhaps a nhs excuse for not spending more money on me!

I try and eat healthy, drink plenty of fluids and yes I do walk and do other exercise when I can. It does help up to a point in my experience, then the fatigue hits hard. Sometimes I can keep exercising through the fatigue, other times I have to give in and listen to what my body is saying.

Good advice about this forum! The best thing I ever did to "treat" my PV was to join this forum. The knowledge, support and empathy you get are second to none. I've made a load of friends most of whom I have never met but they give up their time and energy to help me if I'm down or worried.

Maz, our editor, monitors the forum and can get reliable answers to medical questions from Professor Harrison at Guys. Forums take place up and down the UK - if you go onto to the MPN Voice website, you will see the venues plus get loads of trustworthy information.

Keep in touch, you are not alone.

Kind regards Aime xx😺😺


Hear ,hear ,Aime,excellent reply!!So true.Best to you always,Sally xx

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Hi, my haematolgist told me that I was JAK2 negative - and it was better to be negative than posituve - but not why!!



Hi all,

A late response, but here it is in case it helps.

JAK2 positive means greater chance of thrombosis, and JAK2 negative means less chance, so that's why it is better to be negative.

Here is a link to a paper regarding ET and mutation status if someone is interested:


Best wishes

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Hi. Thank you so much for the information. Can't honestly say I understood it other than JAK 2 negative is the less of two evils! Am seeing my haemo. On 23 August so will ask her to explain it. All I know is that the fatigue is crippling (I also have. CFS) so that doesn't help matters. Am battling on all fronts right now as I am totally isolated. Family all dead as are significant friends and other than medics see no one other than my daughter once a week. Everyone say aaaagh. Thanks again. Mary


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