|Classification and external resources|
49,XXXXX, also known as pentasomy X, penta X, or XXXXX 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
- Small head
- Ear abnormalities
- Widely spaced eyes with upward slanting palpebral fissures and epicanthal folds 
- Short neck
- Broad nose with a depressed nasal bridge
- Hyperextension of the elbows
- Dental abnormalities and cleft palate
- Clinodactyly of the 5th finger
- Deformities of the feet
- Heart defects
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. 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.
- 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 . PMID 15333671. doi:10.1136/jcp.2004.017475.
- 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 . PMID 7218280.
- 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 . PMID 19811657. doi:10.1186/1755-8166-2-20.