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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.
This means that males affected by an X-linked recessive disorder inherited the responsible X chromosome from their mothers. Second, X-linked recessive traits are more commonly expressed in males than females. [2] This is due to the fact that males possess only a single X chromosome, and therefore require only one mutated X in order to be affected.
An X-linked genetic disease is a disease inherited through a genetic defect on the X chromosome. In human cells, there is a pair of non-matching sex chromosomes , labelled X and Y. Females carry two X chromosomes, whereas males have one X and one Y chromosome .
The following is a list of genetic disorders and if known, type of mutation and for the chromosome involved. Although the parlance "disease-causing gene" is common, it is the occurrence of an abnormality in the parents that causes the impairment to develop within the child.
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.
As the X chromosome is one of the sex chromosomes (the other being the Y chromosome), X-linked inheritance is determined by the sex of the parent carrying a specific gene and can often seem complex. This is due to the fact that, typically, females have two copies of the X-chromosome, while males have only one copy.
Females with one affected X chromosome and one normal X chromosome tend to have milder symptoms. Unlike many other types of intellectual disability, the genetics of these conditions are relatively well understood. [2] [3] It has been estimated there are ~200 genes involved in this syndrome; of these ~100 have been identified. [4]
Turner syndrome (Ullrich-Turner syndrome and gonadal dysgenesis) – a condition that describes a female born with only one X chromosome or with an abnormal X chromosome, making her karotype 45,X0. It occurs in 1 in 2,000 to 5,000 females. [ 61 ]