X Chromosome Monosomy
One of the problems a woman with Turner syndrome can have is called X chromosome monosomy, which is the absence of the X chromosome in all cells. In order to diagnose X chromosome monosomy, healthcare providers perform a blood test and look at the chromosomes found in the lymphocytes (a particular type of blood cell).
The cause of Turner syndrome is a problem with one of the two X chromosomes (sex chromosomes).
A woman with Turner syndrome will have one of three possible X chromosome problems:
- Absence of the X chromosome in all cells (called X chromosome monosomy)
- Absence of the X chromosome in some cells (see Mosaic Turner Syndrome)
- Defect of the X chromosome in all cells (see Turner Syndrome and X Chromosome Defects).
During the process in which oocytes (eggs) or sperm are formed, one of the sex chromosomes is sometimes "lost." An embryo receiving only a Y chromosome cannot survive, but an embryo receiving only an X chromosome may survive and develop as a female with Turner syndrome.
In order to examine the matching pairs of chromosomes for a person, doctors can perform a blood test and look at the chromosomes found in the lymphocytes (a particular type of blood cell). This will determine the karyotype of that individual.
The karyotype of X monosomy is termed "45X" -- meaning that an individual has 44 autosomes and a single X chromosome. The usual female karyotype is 46, XX.
(Click Cause of Turner Syndrome for more information on sex chromosomes and the causes of Turner syndrome.)