Karyotype

As statistics show, genetic abnormalities occur in up to 30% of couples affected by infertility. Changes in the genetic material of a woman, her partner or both can cause difficulties in getting pregnant, congenital defects in the fetus and spontaneous miscarriages. One of the basic tests of genetic diagnosis is karyotype testing.

What is a karyotype?

A chromosome is a form of organisation of genetic material. Each chromosome contains genes that are responsible for the proper development and functioning of the human body. A set of chromosomes found in a human somatic cell, i.e. the one that forms the body, except for germ cells (sperm and egg cells), is a called a karyotype. 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 correct karyotype of a man is 46, XY and a woman is 46, XX, where XY chromosomes determine the male sex and XX - the female sex. Karyotype defects may be related to quantitative disturbances of chromosomes and their morphological changes. They are the focus of the geneticist who tests the blood sample collected for karyotype testing.

Karyotype defects resulting from quantitative chromosome abnormalities, are divided into:

• autosomal chromosome trisomies, e.g. the Down syndrome (trisomy 21) or the Edwards syndrome (trisomy 18)
• trisomy of sex chromosomes, e.g. Klinefelter syndrome (additional X chromosome in men: XXY) or XYY syndrome, the so-called superman syndrome.

The second group of chromosome aberrations (abnormalities) are morphological changes, i.e. concerning chromosome morphology. The following can be distinguished:

• translocations, i.e. the displacement of a chromosome fragment,
• inversions, where a fragment of the chromosome is inverted by 180 degrees,
• deletions– the loss of chromosome section,
• duplication - repetition (duplication) of the same chromosome fragment. 

The most common diseases caused by an abnormal karyotype

An abnormal karyotype may be associated with the occurrence of genetic disorders. Below is a list of the most common diseases with the most characteristic symptoms.

• Kinefellter syndrome (additional X chromosome in men) - female body structure, infertility;
• XYY syndrome (additional Y chromosome in men) - so called superman, high body height, correct development, possible lower intelligence quotient;
• XXX syndrome (additional X chromosome in women) - high body height in women, normal phenotype (appearance);
• Turner syndrome (lack of the second X chromosome in women, X chromosome monosomy) - infertility (underdevelopment of primary and secondary sexual characteristics), low height, finned neck;
• Down syndrome (trisomy of the 21st chromosome pair) - characteristic facial features: slanting, small eyes, intellectual disability, infertility;
• Edwards syndrome (trisomy of the 18th chromosome pair) - multi-organ defects, abnormal limb development, intellectual disability;
• Patau syndrome (trisomy of the 13th chromosome pair) - serious lethal malformations, i.e. one eye opening, lack of nose, cleft palate, multi-organ defects. Usually during pregnancy the foetus dies or there is a high risk of delivering a dead baby.

Indications for karyotype examination:

• recurrent miscarriages,
• cases of genetic disorders in the family,
• difficulty conceiving,
• sperm cells concentration below 5 million /mL,
• azoospermia (lack of sperm cells).
• Testing of the couple’s karyotype is mandatory when using the assisted reproduction technique in the form of in vitro fertilisation.

Karyotype test result

The karyotype test result can be collected after 4-6 weeks (up to 30 working days). It is valid for a lifetime, because it does not change during life.

Abnormal karyotype. What next?

Not every abnormal karyotype rules out becoming a parent of a healthy child. Consultation with the geneticist will determine whether the changes in the karyotype may affect the couple’s infertility, as well as possible embryo development and having healthy offspring. In the case of an abnormal karyotype, couples are recommended to perform PGS pre-implantation diagnostics, which is able to determine whether in vitro fertilized embryos do not have karyotype defects. Diagnostics of embryos using the PGS method is also advised to women over 38 years of age due to the increased frequency of genetic defects occurring in egg cells at that age.

Karyotype Preparation for the test.

You do not need to be specially prepared for karyotype testing (no fasting or withdrawal of drugs are required). A drop of venous whole blood is enough to start the test.

Where to perform a karyotype test?

A karyotype test is performed at each InviMed clinic during the working hours of the collection point. You don't need to be registered to undergo a genetic test for chromosome Y mutation.