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As I understand it, Lbrown, a "clone" refers to a cell with a particular set of traits (in the case of diseases, abnormal traits) which can replicate itself and potentially replace normal cells. Cancers are considered clonal disorders because the cancerous cells tend to multiply more rapidly than the healthy ones, but there are also non-cancerous clones. A PNH clone, then, would be a marrow cell which has the characteristics of PNH.
A normal BMB sampling only looks at 20 marrow cells. If only one cell out of the 20 they look at shows abnormal characteristics (whether it's PNH, AML, or a chromosomal mutation like trisomy 8 or 5q deletion), the size of the clone for that disorder is said to be 5%. If 7 out of the 20 have it, the clone is 35%, etc. Clearly with such a small sampling, the margin of error can be pretty high, so it's hard to get a true picture of what's going on without multiple biopsies. If your BMB results consistantly show that 25% of the cells have a particular mutation, then your clone is likely stable. If the percentage increases with every BMB, however, your disease is probably progressing. If it's decreasing, then that's cause for celebration!
Hope this helps,
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-Lisa, husband Ken age 60 dx SAA 7/04, dx hypo MDS 1/06 w/finding of trisomy 8; 2 ATGs, partial remission, still using cyclosporine
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