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Originally Posted by Kjay

I was diagnosed with PNH and AA this past January. Since my first diagnosis, the size of my PNH clone has gone from 1%(RBC)/4%(WBC) to 3%(RBC)/13%(WBC). I don't know if these latest numbers are big, small, medium, etc. Can anyone offer some insight?

Kjay

Kjay,

Stephen King, an AA&MDSIF board member, provided us with an answer to your question, indicating that you have a small clone size.

Stephen said:

The clone size is now considered the single most important factor in trying to develop a prognosis for a PNH patient after a paper co-written by most of the PNH specialists/researchers in the world in 2006. They consider a clone size of over 50% to be high, and under 50% to be low. Part of that is because in a landmark study done by Dr. Hillmen at Leeds in the UK, they found that without treatment, in a period of 2 years, patients with clone sizes over 50% developed at least 1 clot (and in most cases more than 1) that they could measure, while patients with a clone size under 50% didn't develop any clots. (I believe the study had about 80 participants total.)

The 'real' clone size is the % of the stem cells that are defective/missing the CD55 and/or CD59 proteins. Stem cells develop into all cell lines, so you could measure the clone size of RBC's, WBC's, or platelets, and in theory get the clone size/% from that. However, since RBC's with those proteins missing get lysed, if you measure the % of RBC's that are defective, you get a completely inaccurate picture because many of those defective cells are no longer in the blood by the time you measure (peripheraly). So instead, the best measure is to look at the WBC's that are PNH cells. That gives a relatively accurate number. Even then, different labs get fairly different numbers. I've heard of variations as large as 15% between labs.

The bottom line is that measuring the clone size is best/most accurately done by looking at the % of WBC cells (peripherally) that have these defects/are missing the proteins involved, and if the clone size is over 50%, the PNH is considered serious.

There are exceptions where people with clone sizes smaller than 50% have clots (but this isn't common), or have other PNH symptoms, and there certainly are people with clone sizes higher than 50% who don't clot (as far as they know) even without Coumadin or Soliris or another treatment that may prevent clotting.