Human karyotype study
The analysis of the couple's karyotype is a basic genetic test that should be performed by every couple trying for pregnancy. Any abnormality in the karyotype can be the cause of genetic diseases, and these can contribute to infertility or even sterility of the couple. This test also makes it possible to exclude the transmission of genetic defects to the offspring.
As the statistics show, Genetic abnormalities occur even in 30%-50% pairs affected by infertility. Changes in the genetic material of a woman, her partner or both of them can cause difficulties in getting pregnant, spontaneous miscarriages and birth defects in the foetus. One of the basic tests for genetic diagnosis is the karyotype test.
What is a karyotype?
The karyotype is the organism-specific sum of chromosomes with a characteristic number and structure. A chromosome is a thread-shaped structure contained in the cell nucleus, containing the factors of inheritance (genes), consisting of DNA (deoxyribonucleic acid, genetic material) and proteins (usually histones). The genes located in each chromosome are responsible for the normal development and functioning of the human body.
The normal human karyotype consists of 22 pairs of autosomal chromosomes, which determine the inherited characteristics of an individual, and 1 pair of sex chromosomes - allosomes. The normal karyotype of a male is 46, XY and that of a female is 46, XX, where the XY chromosomes determine the male sex and the XX the female sex.
Defects in the karyotype can be related to quantitative abnormalities of the chromosomes and to changes in their structure. These are the focus of the geneticist examining the blood sample submitted for karyotype testing.
Karyotype defects, resulting from quantitative chromosome abnormalities, are divided into:
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trisomies of autosomal chromosomes, e.g. Down syndrome (trisomy 21 of the chromosome) or Edwards syndrome (trisomy 18 of the chromosome)
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sex chromosome trisomies, e.g. Klinefelter syndrome (extra X chromosome in males: XXY) or Jacobs syndrome, the so-called supersex syndrome (XYY).
The second division of chromosomal aberrations (abnormalities) is structural changes, i.e. concerning the structure of the chromosome. Here we distinguish:
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translocations, i.e. movement of a fragment of a chromosome,
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inversions, where a chromosome fragment is inverted 180 degrees,
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deletions - loss of a section of a chromosome,
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Duplications - repetition (duplication) of the same chromosome fragment.
Most common diseases caused by an abnormal karyotype
An abnormal karyotype can be associated with the occurrence of genetic diseases. Below is a list of the most common diseases along with the most characteristic symptoms.
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Kinefellter syndrome (extra X chromosome in males ) - female physique, infertility;
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Jacobs syndrome (extra Y chromosome in males) - so-called super male, high height, normal development, possible lower IQ;
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Syndrome XXX (extra X chromosome in females) - high height in females, phenotype (appearance) normal;
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Turner syndrome (absence of the second X chromosome in females, monosomy of the X chromosome) - infertility (underdevelopment of first and second order sexual characteristics), short stature, flippant neck;
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Down syndrome (trisomy of the 21st pair of chromosomes) - characteristic facial features: oblique, small eyes, intellectual disability, infertility;
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Edwards syndrome (trisomy of the 18th pair of chromosomes) - multiple organ defects, abnormal limb development, intellectual disability;
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Patau syndrome (trisomy of the 13th pair of chromosomes) - severe lethal malformation, i.e. one eye gap, no nose, cleft palate, multiple organ defects. Usually during pregnancy the foetus dies or there is a high risk of stillbirth.
Indications for karyotype testing
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recurrent miscarriages,
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cases of genetic disorders in the family,
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difficulties in conceiving a child,
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a sperm concentration of less than 5 million/ml,
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azoospermia (absence of sperm in the semen).
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Testing of the couple's karyotype is mandatory when using an assisted reproductive technique such as in vitro fertilisation.
According to research, almost 6% of infertile men have an abnormal karyotype, of which 4% are autosomal chromosome disorders and the rest sex chromosome disorders.
Karyotype result
The result of the karyotype test is ready for collection after approximately 4-10 weeks (up to 50 working days). It is valid for life as it does not change during life.
Abnormal karyotype. What next?
Not every abnormal karyotype rules out becoming a parent of a healthy child. A consultation with a geneticist will determine whether changes in the karyotype can affect the couple's infertility, as well as the eventual development of the embryo and having a healthy offspring.
In the case of an abnormal karyotype, couples are advised to undergo preimplantation PGT-A aneuploidy testing, which is able to determine whether embryos resulting from in vitro fertilisation have defects in chromosome number or structure. PGT-A diagnosis of embryos is also advised for women over the age of 35 due to the increased frequency of genetic defects found in egg cells.
Cariotype. Preparation for the test.
You do not need to be specially prepared for the karyotype test (fasting or withdrawal from medication is not required). A drop of whole venous blood is all that is needed to proceed with the test.
Where to have a karyotype test?
Karyotype testing is carried out at every Invimed clinic during collection centre opening hours.
Karyotype price
The price of a karyotype test ranges from £450 depending on the clinic. Current prices can be found in the price lists of the clinics.
