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General Information on Tetrasomy X and Pentasomy X


Tetrasomy X and Pentasomy X syndromes are also known by the descriptions 48, XXXX; 49, XXXXX; 48xxxx; 49xxxx; Tetra X, Penta X, XXXX, XXXXX, or Quadruple X.

Our human genes are located on chromosomes, normally 46 chromosomes divided into 23 pairs. The last of the 23 pairs are called the sex chromosome; males have an X and a Y chromosome, while females have two X chromosomes.

In the case of Tetra X syndrome, females have four X chromosomes instead of two. Therefore, they have 48 chromosomes (48, XXXX) instead of 46. In the case of Penta X syndrome, there are five X chromosomes or a total of 49 chromosomes (49, xxxxx). Tetra/Pentasomy X occurs only in females. There are approximately 60 known females worldwide with this rare condition, although it is believed that there are probably many more who are undiagnosed. The condition was first identified in 1961.

Symptoms can be relatively minor or more severe. They can include learning challenges, social difficulties, congenital heart defects, and various physical attributes common to many chromosome disorders. A description of the physical and developmental characteristics follows.

It should be noted that Tetra/Penta X girls have in some cases gone on to college, enjoy sports, and develop lasting personal relationships. The range of symptoms and severities can be seen by reading through the guestbook entries on this page. It is one of the goals of this support group and web page to begin to document the successes and challenges of Tetra/Penta X girls for the benefit of families and their physicians world wide. We hope to help facilitate research to increase the understanding of this rare condition by the medical community and our families.

Physical and Developmental Characteristics:

Following is a very rough, preliminary summary of the physical and developmental characteristics associated with the diagnosis of tetrasomy X and pentasomy X in females. This is in no way meant to represent a comprehensive analysis of all features associated with these diagnoses. It is important to remember that there is an inherent bias in the collection of this information. All information thus far has been gathered from the on-line support group for families of girls diagnosed with tetra- and pentasomy X. These girls have all been identified medically and/or developmentally. It is therefore possible that the information summarized represents the more “severe” end of the clinical spectrum.

Because of the informal circumstances under which this information has been obtained, it would be inappropriate to use this information in any formal reports.

The information below has been provided by 16 families with tetrasomy X, and four families with pentasomy X.

40% are described as having conotruncal and valvular cardiac defects
10% reported as having abnormal renal structure
15% reported as having visual difficulties (myopia, coloboma, micropthalmus, optic nerve hypoplasia)
~20% report possible seizure activity, no documented abnormal brain function or structure through ECG or MRI
Mild developmental delay reported in >90%, low normal functioning reported in 1 young girl, the remaining children are too young to be assessed


· FFT; failure to thrive
· Hypotonic; low muscle tone (occasional constipation has been reported, possibly related to the hypotonia)
· The majority of girls are reported as being longer and taller, though hypochondrodysplasia (short stature) has been reported in one young girl
· ~50% of the group members (who are of appropriate age) have experienced normal menarche, ~50 % have had either abnormal bleeding or amennhorea. The literature reports 3 women with tetra-X having 4 pregnancies (1 healthy child &1 w/ trisomy 21, 1 stillborn child with omphalocele, and 1 healthy 46,XX female).
· Joint laxity (hips) is reported in ~10 % of the girls in this group and joint limitations are reported in ~20 %, 2 children are reported as having “clubfoot”, and 2 others with “crooked great toes”.
· Facial features include; epicanthal folds, flat nasal bridge, upslanting palpebral fissures(eyes), midface hypoplasia (flattened facial appearance)
· Oral/dental; small mouth, small teeth, failure to develop adult teeth, “floppy” epiglottus (each reported once).
· Dermatoglyphics; clinodactyly (curved) 5th finger, single palmar creases. Linear epidermal nevi and skin tabs each reported once.
· Walking; range from 16 months- 4.5 years
· Speech; variable
· “Rule of thumb”: 10-15 pt decrease from parental IQ per supernumerary (extra) X chromosome.
· As stated above, developmental delay tends to be mild, with speech delay more pronounced than motor delay.
· 2/20 girls in this group have experienced psychiatric symptoms which are well controlled with medications. These symptoms developed at approximately 15 years of age in both girls. In general, 2-3% of all individuals with chromosomal anomalies will experience psychiatric symptoms (“dually diagnosed”). These symptoms are believed to be related to the chromosomal anomaly.
· Majority of girls are described as pleasant, affectionate, shy, with a good sense of humor. Emotional lability tends to coincide with frustrations communicating.

Please remember that this is simply a list of physical and developmental features of which the parent and physician of girls with tetra/pentasomy X should be aware. Speech, Occupational, and Physical Therapy are important aspects in the care of these young girls. The age of diagnosis, implementation of early interventions, and physical complications could all effect the long term prognosis for these children.

This information is meant to be shared amongst families and their daughters’ physicians.


To join the Tetra X/Penta X Support Group, send a blank email to:
tetra-X-list-subscribe@egroups.com (case sensitive) or contact our World Wide Coordinator,
Angela Cooper.

Please email the web host, Tom Stevenson with links, comments, or suggestions for this page. Thank you!


Please share your family's experience with us by signing the guestbook. Include your email address (and web page if you have one) so that others can contact you.

DISCLAIMER: The contents of this web site are not medical, legal, technical or therapeutic advice. The information contained herein is not intended to substitute for informed professional diagnosis, advice or therapy. Visitors should not use this information to diagnose or treat 4X & 5X Syndrome or related disorders without also consulting a qualified medical or educational professional.

© 2002 Tom Stevenson