Trisomy X

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Fluorescent in situ hybridization shows tree copies of the X chromosome in a single cell nucleus.[1]

Trisomy X is a caused by the presence of an extra X chromosome in females (47,XXX instead of 46,XX). This is also the most common female chromosomal abnormality, occurring in approximately 1 in 1,000 female births.

Other abnormalities of chromosome number include: female tetrasomy X (quadruple X, or 48, XXXX) a rare chromosomal disorder and male Klinefelter syndrome, the presence of an additional X chromosome (47, XXY or XXY).

Alternative names: Triplo X syndrome, Trisomy X, 47,XXX, XXX syndrome

Genetic Links: genetic abnormalities | maternal age | Trisomy 21 | Trisomy 18 | Trisomy 13 | Trisomy X | trisomy mosaicism | Monosomy | Fragile X | Williams | Alagille | Philadelphia chromosome | mitochondria | VACTERL | hydatidiform mole | epigenetics | Prenatal Diagnosis | Neonatal Diagnosis | meiosis | mitosis | International Classification of Diseases | genetics

| Genital System - Abnormalities

Some Recent Findings

Human X chromosome
  • A case-control study of brain structure and behavioral characteristics in 47,XXX syndrome[2] "MRI scans were obtained on 35 girls with Trisomy X (mean age 11.4, SD 5.5) and 70 age- and sex-matched healthy controls. Cognitive and behavioral testing was also performed. Trisomy X girls underwent a semi-structured psychiatric interview. Regional brain volumes and cortical thickness were compared between the two groups. Total brain volume was significantly decreased in subjects with Trisomy X, as were all regional volumes with the exception of parietal gray matter. Differences in cortical thickness had a mixed pattern. The subjects with Trisomy X had thicker cortex in bilateral medial prefrontal cortex and right medial temporal lobe, but decreased cortical thickness in both lateral temporal lobes. The most common psychiatric disorders present in this sample of Trisomy X girls included anxiety disorders (40%), attention-deficit disorder (17%) and depressive disorders (11%). The most strongly affected brain regions are consistent with phenotypic characteristics such as language delay, poor executive function and heightened anxiety previously described in population-based studies of Trisomy X and also found in our sample."
  • A review of trisomy X (47,XXX)[3] "Trisomy X is a sex chromosome anomaly with a variable phenotype caused by the presence of an extra X chromosome in females (47,XXX instead of 46,XX). It is the most common female chromosomal abnormality, occurring in approximately 1 in 1,000 female births."
  • Root length in the permanent teeth of women with an additional X chromosome (47,XXX females)[4] "Increased enamel thickness in the teeth of 47,XXX females is apparently caused by the active enamel gene in all X chromosomes having no increased influence on crown dentin formation. These results in 47,XXX females indicate an increase in root dentin development, at least in the mandible, which together with the data on crown formation reflects a continuous long-lasting effect of the X chromosome on dental development."
More recent papers
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Search term: Trisomy X

<pubmed limit=5>Trisomy X</pubmed>

Prenatal Diagnosis

Trisomy X karyotype.jpg

Trisomy X Karyotype[5]

The most common prenatal diagnosis is by either amniocentesis or chorionic villi sampling.

Amniocentesis.jpg Cvs.jpg

Links:Amniocentesis | Chorionic villus sampling

Physical Features

Feature Estimated frequency based on current available data
Tall stature >75th percentile 80 - 89 %
Epicanthal folds 32 - 46 %
Clinodactyly 42 - 65 %
Hypotonia in infancy 55 - 71 %
Genitourinary malformations 5 - 16 %
Seizure disorder 11 - 15 %
Intention tremor 6 - 20 %
Congenital hip dysplasia 2 - 12 %
Constipation/Abdominal pains 12 - 45 %
Premature ovarian failure unknown

Table data from Tartaglia NR, etal., 2010[3]


  1. <pubmed>23162306</pubmed>| Indian J Hum Genet.
  2. <pubmed>25287572</pubmed>
  3. 3.0 3.1 <pubmed>20459843</pubmed>
  4. <pubmed>20568965</pubmed>
  5. 22346085</pubmed>| J Hum Reprod Sci.


<pubmed>20459843</pubmed> <pubmed>17062147</pubmed>


<pubmed>19732877</pubmed> <pubmed>7815443</pubmed> <pubmed>1155452</pubmed> <pubmed>14452136</pubmed>

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Cite this page: Hill, M.A. (2020, October 29) Embryology Trisomy X. Retrieved from

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