Pentasomy X

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Pentasomy X
Other names: 49,XXXXX, penta X, XXXXX syndrome[1]
SymptomsIntellectual disability, short height, low-set ears, decreased muscle tone, developmental delay[1][2]
ComplicationsCongenital heart disease[3]
Causes5 X chromosomes[2]
Risk factorsOlder parents[2]
Diagnostic methodChromosomal analysis[2]
Differential diagnosisDown syndrome, triple X syndrome, tetrasomy X, Turner syndrome[2]
TreatmentBased on symptoms[2]
FrequencyExtremely rare[2]

Pentasomy X, also known as 49,XXXXX, is a chromosomal abnormality in which a female has five X chromosomes instead of the normal two.[2] Signs may include intellectual disability, short height, low-set ears, decreased muscle tone, and developmental delay.[1][2] Complications may include congenital heart disease.[3]

The condition is due to problems during the formation of the reproductive cells in a person's parents.[2] Risk factors include older parents at the time of conception.[2] Diagnosis is suspected based on symptoms and confirmed by chromosomal analysis.[2]

Treatment is based on symptoms.[2] The condition is extremely rare, with less than forty reported cases as of 2011.[2][3] The condition was first described in 1963.[2]

Signs and symptoms

Infant with a presentation of epicanthus, microcephaly, micrognathia

The main characteristics of pentasomy X are intellectual disability, short stature and craniofacial abnormalities.[4] Other physical traits include the following:


The aneuploidy is thought to be caused by problems occurring during meiosis, either in the mother or in both the mother and father. Successive nondisjunctions have been observed in the mother of at least one patient.[4][6]

The features of the syndrome likely arise due to failure of X-inactivation and the presence of multiple X chromosomes from the same parent causing problems with parental imprinting. In theory, X-inactivation should occur and leave only one X chromosome active in each cell. However, failure of this process has been observed in one individual studied. The reason for this is thought to be the presence of an unusually large, and imbalanced, number of X chromosomes interfering with the process.[6]


In terms of diagnosing this condition, can be done via clinical examination and confirmed by chromosomal analysis performed on blood samples to determine if fact it is Pentasomy X[2]


Treatment is specific to the symptom exhibited. In the case of congenital heart defect, medications or surgery may be needed[2]

See also


  1. 1.0 1.1 1.2 "49,XXXXX syndrome". GARD. Archived from the original on 27 May 2019. Retrieved 22 January 2018.
  2. 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 2.15 2.16 "Penta X Syndrome". NORD (National Organization for Rare Disorders). 2003. Archived from the original on 27 May 2019. Retrieved 22 January 2018.
  3. 3.0 3.1 3.2 Beery, Theresa A.; Workman, M. Linda (2011). Genetics and Genomics in Nursing and Health Care. F.A. Davis. p. 105. ISBN 9780803629967. Archived from the original on 2020-08-29. Retrieved 2018-01-22.
  4. 4.0 4.1 4.2 4.3 4.4 4.5 4.6 Cho, Y. G.; Kim, D. S.; Lee, H. S.; Cho, S. C.; Choi, S. I. (2004-09-01). "A case of 49,XXXXX in which the extra X chromosomes were maternal in origin". Journal of Clinical Pathology. 57 (9): 1004–1006. doi:10.1136/jcp.2004.017475. ISSN 0021-9746. PMC 1770429. PMID 15333671.
  5. 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 Monheit, A.; Francke, U.; Saunders, B.; Jones, K. L. (1980-10-01). "The penta-X syndrome". Journal of Medical Genetics. 17 (5): 392–396. doi:10.1136/jmg.17.5.392. ISSN 0022-2593. PMC 1048607. PMID 7218280.
  6. 6.0 6.1 6.2 Moraes, Lucia M.; Cardoso, Leila Ca; Moura, Vera Ls; Moreira, Miguel Am; Menezes, Albert N.; Llerena, Juan C.; Seuánez, Héctor N. (2009-10-07). "Detailed analysis of X chromosome inactivation in a 49,XXXXX pentasomy". Molecular Cytogenetics. 2: 20. doi:10.1186/1755-8166-2-20. ISSN 1755-8166. PMC 2766382. PMID 19811657.

External links

External resources