49, XXXXX

49,XXXXX, also known as pentasomy X, penta X, or XXn XXX syndrome, is an extremely rare chromosomal aneuploidy where females have five X chromosomes rather than the normal two. Prevalence is unknown, but appears to affect fewer than 1 in 100,000 women.

Signs and symptoms

The main characteristics of pentasomy X are intellectual disability, short stature and craniofacial abnormalities.<ref name="Cho 2004">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. ISSN 0021-9746. PMC 1770429 . PMID 15333671. doi:10.1136/jcp.2004.017475. </ref> Other physical traits include the following:

• Small head<ref name="Monheit 1980">Monheit, A.; Francke, U.; Saunders, B.; Jones, K. L. (1980-10-01). "The penta-X syndrome". Journal of Medical Genetics. 17 (5): 392–396. ISSN 0022-2593. PMC 1048607 . PMID 7218280. </ref>
• Ear abnormalities<ref name="Monheit 1980"/>
• Widely spaced eyes with upward slanting palpebral fissures and epicanthal folds <ref name="Monheit 1980"/>
• Short neck<ref name="Monheit 1980"/>
• Broad nose with a depressed nasal bridge<ref name="Cho 2004"/>
• Hyperextension of the elbows<ref name="Cho 2004"/><ref name="Monheit 1980"/>
• Dental abnormalities and cleft palate<ref name="Cho 2004"/><ref name="Monheit 1980"/>
• Clinodactyly of the 5th finger<ref name="Cho 2004"/><ref name="Monheit 1980"/>
• Deformities of the feet<ref name="Cho 2004"/><ref name="Monheit 1980"/>
• Heart defects<ref name="Moraes 2009">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. ISSN 1755-8166. PMC 2766382 . PMID 19811657. doi:10.1186/1755-8166-2-20. </ref><ref name="Monheit 1980"/>

Causes

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.^[1][2] 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.^[2]

See also

• Trisomy X
• Tetrasomy X

References

External links

• Tetrasomy & Pentasomy X Syndrome Information and Support