Cytogenetic tests are often carried out on leukemia patients to detect any chromosomal abnormalities associated with their disease. Trisomy is a chromosomal defect that involves the presence of an additional whole chromosome.

Every cell in the human body (with the exception of ovum and sperm) has 46 chromosomes. There are 22 pairs of chromosomes called somatic chromosomes plus the 2 sex chromosomes. As each cell prepares to undergo the usual process of cell reproduction (mitosis), it doubles the number of chromosomes and then splits into 2 cells, each with 46 chromosomes. Or at least that is how it is supposed to work.

Every now and again, three copies of a chromosome will go into one cell giving the cell a trisomy of a specific chromosome, and the remaining copy goes into the other cell resulting in a monosomy. Usually both of these circumstances result in the death of both cells, but occasionally, a cell can live to produce a cell line that is unique, and unfortunately, unique cell lines can be malignant.

Trisomy 12, the presence of an additional 12th chromosome, is a trisomy that is frequently found in CLL patients. The defect responsible for trisomy 12 in CLL is not known. Studies suggest that CLL patients with such chromosomal abnormalities carry a poorer prognosis than patients with normal chromosomes.

We don't know exactly what causes these trisomies, and much more important, regardless of what the Human Genome project press releases say, we really don't know what information is where or what it means. So, all we can do at this stage is note that certain diseases seem to have certain trisomies, or monosomies.