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Turner syndrome (TS), commonly known as 45,X, or 45,X0, [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. [2] [6] [7] Most people have ...
The parents of the affected individual are usually genetically normal. [14] The incidence of the syndrome increases with the age of the mother, from less than 0.1% for 20-year-old mothers to 3% for those of age 45. [4] It is believed to occur by chance, with no known behavioral activity or environmental factor that changes the probability. [2]
In the wake of the establishment of the normal number of human chromosomes, 47,XYY was the last of the common sex chromosome aneuploidies to be discovered, two years after the discoveries of 47,XXY, [27] 45,X [28] and 47,XXX [29] in 1959. Even the much less common 48,XXYY [30] had been discovered in 1960, a year before 47,XYY.
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.
Chromosomes in Down syndrome, the most common human condition due to aneuploidy. There are three chromosomes 21 (in the last row). A chromosomal disorder is a missing, extra, or irregular portion of chromosomal DNA. [33] It can be from an atypical number of chromosomes or a structural abnormality in one or more chromosomes.
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 ...
This option is particularly important for the few (less than 20%) MDS families where one parent carries a balanced chromosome rearrangement. The risk of these couples having another child with MDS depends on the exact type of chromosomal rearrangement present and may be as high as 25–33%.
In July 2012, the fourth "CdLS gene"—HDAC8—was announced. HDAC8 is an X-linked gene, meaning it is located on the X chromosome. Individuals with CdLS who have the gene change in HDAC8 make up just a small portion of all people with CdLS. [8] Evidence of a linkage at chromosome 3q26.3 is mixed. [9]