CHROMOSOME ANALYSIS TISSUE
Also Known As: karyotyping, genetic testing, chromosome studies, cytogenetic analysis.
What Is Chromosome Analysis Tissue Test?
The test is used to find any abnormality or defect in the number, size, and shape of the chromosomes. Chromosomes are found in the nucleus of every body cell, making up your body’s DNA or genetic road map. DNA is a thread-like structure, but when the cell divides, DNA breaks into pieces called chromosomes. The chromosome contains thousands of genes at specific locations that direct your body growth, development, and function; it also holds specific body traits like hair, eye, skin color, and blood type.
Every human cell comprises 23 pairs of chromosomes which are 46 chromosomes in total, of which 22 pairs are autosomes, and they are the same in both sexes. In contrast, one pair is called the sex chromosome (X and Y), which determines the gender of the body; the male has XY, and the female contains XX configuration of chromosomes. Each parent contributes half of the set (one pair) to their newborn during conception. Any abnormality in the structure and number of chromosomes may lead to congenital disabilities, miscarriages, developmental delays, or other health issues.
What Is The Test Used For?
Chromosome analysis helps diagnose health conditions caused by abnormalities in the genetic material of the cells before the symptoms appear, either before birth or after birth. It may also predict the health problems that a baby may be born with or develop later in life. The tissue sample is cultured in a nutrient-containing medium that promotes cell growth. When enough cells are grown, chromosomes are isolated from their nucleus, dyed, and observed under the microscope, where microphotographs are captured. A computer imaging program is used to pair and arrange them according to their size, from largest to smallest, followed by sex chromosomes. A lab technician interprets these images and finds the abnormalities in the size, shape, number, and arrangement of chromosomes. Any extra or missing chromosome or piece of a chromosome is detected and reported.
About half of the first trimester miscarriages are associated with fetal chromosome defects. In some cases, where fetal chromosome karyotyping shows structural rearrangements, parental chromosome analysis may be required to evaluate the cause and thus help limit the risk for future fetal losses and birth of a chromosomally abnormal child. Most common abnormalities that can be detected by chromosome analysis tissue test include:
- TRISOMIES (presence of one extra chromosome) like Down Syndrome (trisomy 21), trisomy 18. Trisomy 13.
- SEX CHROMOSOME ABNORMALITIES, including Turner syndrome and Klinefelter syndrome.
- REARRANGEMENTS like Robertsonian translocation, chronic myeloid leukemia (CML), and many inversions.
- MOSAICISM above 14%
However, the test cannot detect all genetic problems, so further testing may be required.
Why And When Do You Need To Get Tested?
This test is used to screen and diagnose chromosomal abnormalities in a fetus or newborn suspected of having them. Your healthcare provider may order this test:
- If you have a known genetic disorder in the family line that may pass into your children.
- To diagnose a chromosomal disorder in a newborn or young child with congenital disabilities.
- To find out the cause of recurrent or spontaneous first trimester miscarriages.
- When pregnancy screening tests suggest abnormally developed fetus and intrauterine growth retardation (IUGR).
- Loss of pregnancy after Invitro fertilization (IVF).
Your healthcare professional may also request some other tests for further evaluation.
What Kind Of Sample Is Required?
In case of stillbirth or miscarriage, the product of conception is collected in a sterile container and transported to the laboratory. The preferred products of conception are chorionic villi, placenta, placental membranes, and umbilical cord blood; however, the whole product of conception or part of fetal organs can also be submitted.
For screening of viable fetuses during pregnancy, tissue samples are taken from chorionic villi by a procedure called chorionic villus sampling (CVS), in which a catheter or a needle is used to biopsy the placental cells. Another method of sampling fetal cells is amniocentesis, in which amniotic fluid that surrounds the fetus is collected using a long needle. Both procedures require expertise and are usually performed by well-trained healthcare professionals.
Do You Need To Prepare For This Test?
You don’t require special preparation for this test; however, while performing CVS and amniocentesis, you may be asked to avoid going to the toilet for a few hours. A full bladder will help the uterus to lift us and thus make sampling easy. Moreover, be sure you have been
informed about all medications you are taking recently.
Are There Any Risks To This Test?
Each method of sampling has certain risks. CVS and amniocentesis can lead to miscarriages; amniocentesis has a slightly lower risk of miscarriage than CVS. You may also experience bleeding, pain, and sting at the site of the needle prick, and rarely may you develop an infection.
What Does The Test Result Mean?
The results are usually obtained between 14-28 days. Normal chromosomes are reported as:
- 44 autosomes plus two X chromosomes for females (46XX)
- 44 autosomes plus one X and one Y for males (46XY).
Abnormal results are interpreted by a person who is specialized in cytogenetics. Some chromosomal disorders are straightforward, while others are complex and difficult to predict reliably. Some examples of chromosomal abnormalities are:
- Down syndrome (trisomy 21)
- Patau syndrome (Trisomy 13)
- Edward syndrome (Trisomy 18)
- Klinefelter syndrome (where a male has an extra X chromosome – XXY instead of XY).
- Turner syndrome (monosomy in which a female has a single X chromosome – X instead of XX)
- Many blood cancers are also associated with chromosomal abnormalities, including CML with classic 9;22 translocations.
Each syndrome has typical signs and symptoms, which along with the test report, help your healthcare provider diagnose. You should consult your healthcare practitioner if you have any queries regarding your test results.
- Chromosomal microassay
- Fluorescence in-situ hybridization (FISH)
- Product of conception penal
- Amniotic fluid testing
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