XXXXX syndrome

XXXXX syndrome
Classification and external resources
Specialty	medical genetics
ICD-10	Q97.1
DiseasesDB	32625
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XXXXX syndrome (also called pentasomy X or 49, XXXXX) is a type of aneuploidy (an abnormal number of chromosomes) which results in the presence of three additional X chromosomes. The condition was first described in 1963. It is characterized by severe intellectual disability, short stature and abnormalities to the head and face. As these features can be seen in other conditions, karyotyping must be carried out to confirm diagnosis. There have been cases of XXXXX syndrome being misdiagnosed as Down syndrome.

It is an extremely rare condition with no more than 30 patients reported in medical literature. The exact incidence is not known but it may be similar to the rate of 1 in 85,000 seen in males with 49, XXXXY syndrome.

The main characteristics of XXXXX syndrome are intellectual disability, short stature and craniofacial abnormalities. 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. 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.

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