Interpreting A Karyotype Description

Receiving a cytogenetic report that contains the description of a patient's karyotype can create confusion, particularly if complex rearrangements or multiple clones are present. Interpretation of the description of a karyotype can be facilitated by breaking this description into its component parts.

First, determine whether more than one cell line is present. This will happen if constitutionally the patient is a mosaic or a chimera as is often the case with acquired cytogenetic abnormalities, particularly in patients whose neoplasm is progressing. Because the first item described is always the number of chromosomes present, each clone or cell line present will start with this number, and each is separated by a slash (/). Each cell line can then be examined individually. If abnormalities present in the first clone listed are also present in others, the description can be simplified by using the abbreviation "idem" to indicate this; note that idem always refers to the first cell line described, which will be the stemline in these cases.

As discussed above, the sex chromosome complement follows the chromosome count. Sex chromosome abnormalities are listed first, followed by autosomal abnormalities in numerical order. When abnormalities involve the same chromosome, numerical changes are presented first, followed by structural abnormalities listed in alphabetical order, using the abbreviations listed in Table 3.

Commas separate each abnormality listed, and so by examining the karyotype from comma to comma, the abnormalities involved can be interpreted.

Consider the following example from a patient with AML:


At first blush, receiving a report with this karyotype might be enough to scare away even the most confident clinician! However, let us break this karyotype down into its component parts, which will simplify its interpretation.

The slashes, brackets, and listings of number of chromosomes tell us that three different clones are present:

Of the 20 cells examined, the first clone has 47 chromosomes and is represented by 4 cells. The second clone has 48 chromosomes; 12 of these cells were observed. Finally, four normal 46,XY cells are present.

Now, let us look again at the first cell line, the stemline in this case. It has an XY sex chromosome complement. It also has three cytogenetic abnormalities: It has one chromosome 5 with an interstitial deletion of the material between bands q13 and q33 (on the long arm):

47,XY,del(5)(q13q33),+8,t(9;22)(q34;q11.2)[4]/48,idem,+9,i(17)(q10)[12]/46,XY[4] \

It has an extra copy of chromosome 8,

47,XY,del(5)(q13q33),+8,t(9;22)(q34;q11.2)[4]/48,idem,+9,i(17)(q10)[12]/46,XY[4] \

and it has a translocation involving the long arms of chromosomes 9 and 22, at band q34 of chromosome 9 and band q11.2 of chromosome 22:


Yes, this is the "Philadelphia" rearrangement, which is sometimes also seen in patients with AML. The second cell line contains the sex chromosomes and all of the abnormalities present in the first:


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