Pathogenesis (development of disease)
Chromosomes are strands of deoxyribonucleic acid (DNA) with so-called histones (basic proteins within a nucleus) and other proteins; the mixture of DNA, histones, and other proteins is also called chromatin. They contain genes and their specific genetic information.
In the human body, the number of chromosomes is 46, with 23 inherited from each parent. Chromosomes are divided into autosomes and gonosomes (sex chromosomes). The chromosome pairs 1 to 22 are autosomes, the 23rd chromosome pair are the sex chromosomes (XY in male and XX in female).
In Turner syndrome, a defective distribution of chromosomes (chromosomal abnormality) occurs during meiosis (maturation division), resulting in the presence of only one sex chromosome, the X chromosome, in all or only part of the body cells.
In more than 50% of affected women there is a complete loss of one X chromosome. There are 45 chromosomes in all body cells instead of 46 chromosomes (ICD 10 Q96.0 karyotype 45,X).
In 30-40% of cases, although there are 46 chromosomes in all somatic cells, there are structural changes in another X chromosome (ICD 10 Q96.1 karyotype 46,X iso (Xq) and Q96.2 karyotype 46,X with gonosome abnormality, except iso (Xq)).
In 10-20% of cases there are mosaic changes within one chromosome. Here, some somatic cells have the complete chromosome set of 46 with the possible chromosome constellations of XX or XY, but others have a chromosome set of 45 due to the presence of only one X chromosome (ICD 10 Q96.3 mosaic, 45,X/46,XX or 45,X/46,XY).
In rarer cases, mosaic changes are detected in which some somatic cells have 45 chromosomes but the others have difficult-to-identify gonosomal abnormalities (abnormalities of sex chromosomes) (ICD 10 Q96.4 Mosaic, 45,X/other cell line(s) with gonosomal abnormality).
In mosaic abnormalities, symptomatology and possible sequelae are milder.
Etiology (Causes)
Biographic causes
- Spontaneous mutations
- Complete absence of an X chromosome
- Structural alteration of an X chromosome
- Mosaic changes of both or one X chromosome.
