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Turner syndrome (TS), commonly known as 45,X, or 45,XO, [note 1] is a chromosomal disorder in which cells have only one X chromosome 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.
Eric Engel first proposed the concept of uniparental disomy in 1980 as both homologous chromosomes are inherited from one parent, with no contribution (for that chromosome) from the other parent. [ 11 ] [ 12 ] Eight years later in 1988, the first clinical case of UPD was reported and involved a girl with cystic fibrosis and short stature who ...
Rather than having monosomy, or only one copy, the majority of aneuploid people have trisomy, or three copies of one chromosome. [citation needed] An example of trisomy in humans is Down syndrome, which is a developmental disorder caused by an extra copy of chromosome 21; the disorder is therefore also called trisomy 21. [7]
[1] [2] It does not include a difference of one or more complete sets of chromosomes. A cell with any number of complete chromosome sets is called a euploid cell. [1] An extra or missing chromosome is a common cause of some genetic disorders. Some cancer cells also have abnormal numbers of chromosomes.
Monosomy, with the presence of only one chromosome (instead of the typical two in humans) from a pair, which affects chromosome 14. Fetuses with monosomy 14 are not viable. [ 1 ] Only mosaic cases exist and these usually present with severe symptoms such as intellectual disability , ocular colobomata , microcephaly , and seizures .
The syndrome is defined by the presence of at least one extra X chromosome in addition to a Y chromosome, yielding a total of 47 or more chromosomes rather than the usual 46. Klinefelter syndrome occurs randomly. The extra X chromosome comes from the father and mother nearly equally.
Human conditions due to monosomy: Turner syndrome – Females with Turner syndrome typically have one X chromosome instead of the usual two X chromosomes. 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.
X-linked recessive traits are more common in males as they only have one X chromosome, they need only one mutated X chromosome to be affected. In contrast, females have two X chromosomes and must inherit two mutated recessive X alleles, one from each parent, to be affected. X-linked recessive phenotypes tend to skip generations. [7]