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The types of Turner Syndrome (TS) are determined by the specific nature of the X chromosome abnormality. These classifications include:
Monosomy X
In this type, each cell contains only one X chromosome instead of the usual two (45,X karyotype). Monosomy X accounts for approximately 45% of all TS cases. This chromosomal error occurs randomly during the formation of an egg or sperm lacking an X chromosome. Consequently, all cells in the developing embryo will exhibit this single X chromosome.
Mosaic Turner Syndrome
Also known as X-chromosome mosaicism, this variant constitutes about 30% of Turner Syndrome cases. Individuals with mosaic TS possess a mixture of cell lines: some cells have two X chromosomes (e.g., 46,XX), while others have only one (45,X). This condition arises spontaneously from an error in cell division during the early stages of embryonic development.
Structural X Chromosome Abnormalities (Sometimes referred to as "Inherited Turner Syndrome" in broader contexts)
In rare instances, Turner Syndrome can be associated with an X chromosome that has a structural abnormality (e.g., a deletion of part of an X chromosome, or an isochromosome). While classical monosomy X is almost always a sporadic event, some structural abnormalities of the X chromosome can be inherited from a parent, leading to features of Turner Syndrome in the child. This form typically involves a partial loss or rearrangement of the X chromosome's genetic material.
What are the types of Turner Syndrome?
Monosomy X
In this type, each cell contains only one X chromosome instead of the usual two (45,X karyotype). Monosomy X accounts for approximately 45% of all TS cases. This chromosomal error occurs randomly during the formation of an egg or sperm lacking an X chromosome. Consequently, all cells in the developing embryo will exhibit this single X chromosome.
Mosaic Turner Syndrome
Also known as X-chromosome mosaicism, this variant constitutes about 30% of Turner Syndrome cases. Individuals with mosaic TS possess a mixture of cell lines: some cells have two X chromosomes (e.g., 46,XX), while others have only one (45,X). This condition arises spontaneously from an error in cell division during the early stages of embryonic development.
Structural X Chromosome Abnormalities (Sometimes referred to as "Inherited Turner Syndrome" in broader contexts)
In rare instances, Turner Syndrome can be associated with an X chromosome that has a structural abnormality (e.g., a deletion of part of an X chromosome, or an isochromosome). While classical monosomy X is almost always a sporadic event, some structural abnormalities of the X chromosome can be inherited from a parent, leading to features of Turner Syndrome in the child. This form typically involves a partial loss or rearrangement of the X chromosome's genetic material.