The following chromosome studies may help to determine whether a child has a genetic birth defect:
In a karyotype, the chromosomes can look bent or twisted. This is normal and is a result of how they were sitting on the slide when the photograph was taken. Chromosomes are flexible structures that condense and elongate during different stages of cell division. If you unraveled all of the DNA that makes up the 46 chromosomes, you would find over 7 feet of DNA from one single cell.
For example, if a baby is suspected of having trisomy 21 Down syndrome and an amniocentesis is done on the pregnancy, a FISH study can be performed on the cells found in the amniotic fluid. A probe made for chromosome #21 can determine how many copies of the #21 chromosome the baby has. Under a special microscope, the cells from a baby with trisomy 21 would contain three "signals" or three brightly colored areas, where the probe matched up with the three #21 chromosomes. A FISH study does not replace a chromosome study, but is done in addition to a standard chromosome study, depending on the birth defect in question.
FISH can be used to detect structural chromosome abnormalities (such as submicroscopic deletions) that are beyond the resolution of extended banding chromosome studies.
"Telomere" is a term used to describe the very ends of chromosomes. When FISH is used specifically to look for chromosome abnormalities in this area, it is referred to as "subtelomeric FISH testing."
Click here to view the
Online Resources of Medical Genetics
|Pocket Doc Mobile App|
|Maps and Locations (Mobile)|
|Programs & Services|
|For Health Professionals|
|For Patients & Families|
|Find a Doctor|