Human karyotype
A karyotype is an individual's complete set of chromosomes. The term also refers to a laboratory-produced image of a person's chromosomes isolated from an individual cell and arranged in numerical order. A karyotype may be used to look for abnormalities in chromosome number or structure.
Normally, the human karyotype consists of 23 pairs of chromosomes: 22 pairs are called autosomes, and the last pair - sex chromosomes. Such a karyotype remains unchanged throughout life.
The female sex in humans is homogametic, that is, it has two X chromosomes. Male - heterogametic, has an X and a Y chromosome.
Chromosomal abnormalities have both quantitative and structural changes. Any amount chromosomes, in addition to 46, is a change in the amount of standard genetic material and can cause health and developmental problems. As for structural changes, the significance of the problems and their severity depend on the chromosome, which is subject to change.
Some human diseases caused by karyotype abnormalities 47, XXY; 48, XXXY; Klinefelter's syndrome — polysomy on the X chromosome in men;
45X0; 45X0/46XX; 45, X/46, XY, 46 a, X iso (Xq) Shereshevsky-Turner syndrome — monosomy on the X chromosome, including mosaicism;
47, XXX; 48, XXXXX, 49, XXXXXX polysomy on the X chromosome, in fact - trisomy X;
47, XX, 21 +; 47, XY, 21 + Down syndrome — trisomy on the 21st chromosome;
47, XX, 18 +; 47, XY, 18 + Edwards syndrome — trisomy on the 18th chromosome;
47, XX, 13 +; 47, XY, 13 + Patau syndrome — trisomy on the 13th chromosome;
46, XX, 5p- Cat cry syndrome — deletion of the short arm of the 5th chromosome;
46 ХХ or ХУ, 15Р-. Prader-Willi syndrome is an anomaly of chromosome 15.
A chromosome analysis (karyotype) test is the only test that can confirm a triploidy diagnosis. This test counts the number of chromosomes in a fetus’s genes to determine the existence of extra chromosomes.
To perform this test, a doctor needs a tissue sample from the fetus. Because the fetus and placenta come from the same fertilized egg, a doctor can use a placenta sample for testing.
An amniocentesis can also be used to diagnose triploidy. The doctor extracts amniotic fluid and then analyzes the sample for signs of abnormal chromosomes.
Triploidy may be suspected prenatally, or before the baby is born, if a maternal serum screening test is ordered and has certain abnormalities. This blood test, typically performed during the second trimester of pregnancy, is not designed to detect the condition. However, unusual test results such as too much or too little of certain proteins in the blood, can alert an obstetrician to potential problems. More tests may be needed if a serum screening test has abnormal results.
Triploidy can also be suspected during an ultrasound, which is commonly performed during pregnancy to examine the fetus. This test can help the doctor see if a fetus has certain anatomic abnormalities.
Carrying a baby with triploidy doesn’t increase your chances of another similar pregnancy, so it’s safe to conceive another child without having to worry about a higher risk of another baby with triploidy. If you do decide to have another child, continue to seek prenatal care and testing to make sure that your baby receives the best care possible.