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Turner syndrome (TS), commonly known as 45,X, or 45,X0, [note 1] is a chromosomal disorder in which female cells have only one X chromosome instead of two, or are partially missing an X chromosome (sex chromosome monosomy) leading to the complete or partial deletion of the pseudoautosomal regions (PAR1, PAR2) in the affected X chromosome.
The tip of the Y chromosome contains the SRY gene and, during recombination, a translocation occurs in which the SRY gene becomes part of the X chromosome. [15] [26] If a fetus is conceived from a sperm cell with an X chromosome bearing the SRY gene, it will develop as a male despite not having a Y chromosome. This form of the condition is ...
In males (who have only one X chromosome), one altered copy of the gene in each cell is sufficient to cause the condition. In females (who have two X chromosomes), a mutation must be present in both copies of the gene to cause the disorder. Males are affected by X-linked recessive disorders much more frequently than females.
Males with Klinefelter syndrome typically have one extra copy of the X chromosome in each cell, for a total of two X chromosomes and one Y chromosome (47,XXY). It is less common for affected males to have two or three extra X chromosomes (48,XXXY or 49,XXXXY) or extra copies of both the X and Y chromosomes (48,XXYY) in each cell.
For people with disorders like trisomy X, where the genotype has three X chromosomes, X-inactivation will inactivate all X chromosomes until there is only one X chromosome active. Males with Klinefelter syndrome, who have an extra X chromosome, will also undergo X inactivation to have only one completely active X chromosome.
In Turner syndrome, a chromosomal abnormality in which a person exhibits X chromosome monosomy, patients are at a great risk of developing autoimmune thyroid disease since their genotype mimics an extreme form of X chromosome inactivation since there is only one X chromosome that can be expressed.
The estimate suggests that the condition is slightly less common than Rett syndrome, a genetic disorder that causes babies to rapidly lose coordination, speech and mobility and affects about 1 in ...
Turner syndrome is the only full monosomy that is seen in humans — all other cases of full monosomy are lethal and the individual will not survive development. Cri du chat syndrome – (French for "cry of the cat" after the persons' malformed larynx ) a partial monosomy caused by a deletion of the end of the short arm of chromosome 5