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Trisomy X, also known as triple X syndrome and characterized by the karyotype [note 1] 47,XXX, is a chromosome disorder in which a female has an extra copy of the X chromosome. It is relatively common and occurs in 1 in 1,000 females, but is rarely diagnosed; fewer than 10% of those with the condition know they have it.
Fragile X syndrome is a genetic disorder which occurs as a result of a mutation of the Fragile X Messenger Ribonucleoprotein 1 (FMR1) gene on the X chromosome, most commonly an increase in the number of CGG trinucleotide repeats in the 5' untranslated region of FMR1.
The first trinucleotide repeat disease to be identified was fragile X syndrome, which has since been mapped to the long arm of the X chromosome. Patients carry from 230 to 4000 CGG repeats in the gene that causes fragile X syndrome, while unaffected individuals have up to 50 repeats and carriers of the disease have 60 to 230 repeats.
46, XX male syndrome, also known as de la Chapelle syndrome In this list, the karyotype is summarized by the number of chromosomes, followed by the sex chromosomes present in each cell. (In the second and third cases the karyotype varies from cell to cell, while in the last three cases, the genotype is normal but the phenotype is not.)
Fragile X syndrome is caused by expansion of CGG repeats in the FMR1 gene. In males without fragile X syndrome, the CGG repeat number ranges from 53 to 200 while those affected have greater than 200 repeats of this trinucleotide sequence located at the end of the X chromosome on band Xq28.3.1. [36]
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.
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.
In 1959, five days after Jérôme Lejeune described the trisomy-21 [3] in Down syndrome, basing himself off Marthe Gautier's work, [4] Jacobs and John Strong described an additional X chromosome in male patients (the 47,XXY karyotype) [5] also known as Klinefelter syndrome, as Harry Klinefelter had already diagnosed the symptoms in 1942.