Reasons for a Karyotype

A karyotype can diagnose any chromosomal problems you may have

Male Karyotype. Credit: Media for Medical / Contributor / Getty Images

A karyotype is a picture of all of the chromosomes present in a single one of your cells. Often times doctors will order a karyotype to check for chromosomal abnormalities and diagnose rare diseases. 

A karyotype can tell how many chromosomes you have, as well as any errors those chromosomes may have. Normally, a person has 23 pairs of 46 chromosomes. If you have two X chromosomes, you are biologically a female.

Having an X and a Y chromosome means you are biologically a male.

How Karyotypes Are Performed 

If your doctor has ordered a karyotype, you will need to have blood drawn for analysis. Your sample will most likely be gathered from blood that was drawn during a doctor’s appointment, hospital, or a trip to a testing laboratory. If you are pregnant, a karyotype for your child will be done from either a sample of amniotic fluid or chorionic villi. Amniocentesis and chorionic villus sampling procedures are a bit more invasive than a blood test—both require a needle to be inserted into your abdomen—however, they are relatively painless procedures.

After your sample is collected, it will be analyzed by a special cytogenetics laboratory. The cytogenetic specialist analyzing your sample will separate your cells, grow them so that they have enough to analyze, and then release the chromosomes from the cells.

Once the chromosomes are released, they are stained, analyzed, counted to see if you have more or less than the normal 46 chromosomes, and sorted. The cytogeneticist will also look at the structure of your chromosome to make sure there is no missing or added genetic material. Once this process is complete, the findings are written up for your doctor to share with you.

For karyotypes done on blood samples, results should be available within three to seven days. The results of karyotypes on prenatal samples take a bit longer—anywhere from 10 to 14 days.

What Karyotypes Say About Your Health

Based on your karyotype, cytogeneticists, people who study chromosomes, can diagnose any condition that results from extra or missing chromosomes. In addition to Down syndrome (trisomy 21), a karyotype can determine if you have:

  • Edward syndrome (trisomy 18)
  • Patau syndrome (trisomy 13)
  • Turner syndrome (one X)
  • Klinefelter syndrome (XXY)
  • XYY syndrome
  • Triple X syndrome (XXX)

Karyotypes can also determine whether your chromosomes have any deletions—such as Cri-du-Chat syndrome (chromosome 5) or Williams syndrome (chromosome 7)—or if that have translocations, where one part of a chromosome is found on or switched with another part of a different chromosome. Karyotypes can detect both reciprocal and Robertsonian translocations. About 2 percent to 3 percent of Down syndrome cases are caused by a translocation on chromosome 21. Robertsonian translocations can also cause Patau syndrome, Angelman syndrome, and Prader-Willi syndrome.

If you, or your child, has Down syndrome or a trisomic condition, ​karyotypes taken from an assortment of different cells can determine whether or not you have a mosaic trisomy.

Mosaicism means the trisomy is present in some cells and not others.

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