The normal human karyotype has two sets of chromosomes, one set inherited from each parent, so that we have 46 chromosomes (22 pairs, including either an XX if you’re a female, or XY if male). But sometimes during cell division of the zygote (early in fertilization), the chromosomes don’t divide properly into their respective cells and the developing fetus carries an abnormal number of chromosomes in all cells of the body (termed aneuploidy). Usually the fetus does not survive into full term, but in some cases when the baby does, a rare chromosome disorder happens.
Trisomy happens when there are three copies of a chromosome, instead of the normal two copies.
Take for example Down Syndrome, which is caused by an extra copy of chromosome 21, resulting in 47 chromosomes. Every person with Down’s Syndrome has the characteristic asymmetrical skull, slanting eyes, stocky build and some degree of mental retardation.
The Triple-X Syndrome is caused by, obviously, an extra X chromosome in each of a female’s cells (XXX), and girls are taller, thinner and have a higher incidence of dyslexia.
Klinefelter’s Syndrome is caused by an extra X chromosome in a male (XXY), and the men tend be shy and quiet, are taller with longer legs and arms, and have a higher incidence of dyslexia. The men are also sterile and so can not pass on the disorder to the next generation.
There is also Trisomy-8 mosaicism, where there are some cells in the body with an extra copy of chromosome 8, while other cells have the normal number, and the symptoms are far-ranging.
As you can see, having a trisomy or chromosome abnormality is difficult for the individuals and families involved. With proper management of the symptoms, rehabilitation and therapy, these individuals can live some comfortable level of quality-of-life.
It was heartwarming to come across this website – www.rarechromo.org – that is a wonderful support group for the families and professionals treating them.
Post from: Genetics & Health


