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What

Tetrasomy X is a genetic condition in which females have 4 X chromosomes instead of the usual 2. Individuals with tetrasomy X show a very wide range of signs and symptoms, but in general they are tall and have problems with their vision, muscle tone, fertility, learning, behavior, and/or development.

Who

Tetrasomy X affects only females and is rare. Only females are affected because females have X chromosomes as their sex chromosomes and males have an X and a Y chromosome.

Signs and Symptoms

Girls with tetrasomy X usually present in early childhood and are slim and much taller than would be expected compared to their other family members. Typical signs and symptoms vary a great deal but can include: • distinctive facial features • vision problems that include myopia (nearsightedness) and nystagmus (uncontrolled movements of the eye) • difficulty with hearing due to frequent ear infections, sound blockage or nerve abnormalities • the mouth and teeth are often unusual; they can have small mouths, cleft or high arched palates, delayed or absent teeth, or enamel defects • joint and muscle tone abnormalities; particularly hypotonia (decreased muscle tone) and joint looseness in the hips • Skeletal problems include; abnormal curvatures of the spine • cardiac defects such as ventricular/atrial septal defects (holes in the heart), atresia (narrowing of the heart valves), hypoplastic right heart syndrome (underdeveloped right side of the heart), or patent ductus arteriosus (failure of normal closure of a fetal hole in the heart) • abnormal kidneys • wide variability in ovarian function, fertility, and reproductive development. About 50% of patients undergo normal puberty, while the other 50% experience no puberty at all, partial puberty without secondary sexual characteristics, or complete puberty with menstrual irregularities and/or early menopause (as early as the teens) • behavior and neurological/mental development. Mild developmental delay is reported in over 90% of girls with tetrasomy X and the average IQ is 60-70. Patients show significant delays in speech development and articulation, language expression and understanding, and reading skills.

Possible Causes

Tetrasomy X is a type of sex chromosome aneuploidy, which simply means an abnormal number of sex chromosomes. In most cases the extra X chromosomes occur when the sex chromosomes do not separate properly in the egg or sperm. The addition of this extra genetic material in a child affects the major areas of development. It is believed that because the genes necessary for normal ovarian development are found on the X chromosome, abnormalities of X chromosomes lead to low estrogen levels and infertility. In other systems, for yet unknown reasons, increasing numbers of sex chromosomes are predictors of increasing severity of clinical findings—for example, IQ decreases 10-15 points for each extra X chromosome

Diagnosis

Tetrasomy X is initially suspected based on finding the above described signs and symptoms on physical examination. The diagnosis is confirmed by a special laboratory test where the chromosomes of a child are examined under a microscope. This test, a karyotype, will show the extra X chromosomes.

Treatment

The treatment for girls with tetrasomy X has typically been management of symptoms and support for learning. Most commonly, girls are placed on estrogen treatment, which induces breast development, stops longitudinal growth, and stimulates bone formation to prevent osteoporosis. Speech, occupational, and physical therapy may also be needed depending on severity of symptoms, but studies have shown that the most important factors in minimizing the negative effects of the condition are a supportive family and healthy environment.

Prognosis

The prognosis for girls with tetrasomy X is very good, particularly for those with strong family support who receive professional help at the first signs of any learning or medical problems. While some girls with tetrasomy X have gone on to college, some have needed help throughout their lives, showing the great variability of this syndrome.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

Tetrasomy & Pentasomy X Syndrome: Information and Support
Support website for parents of children with tetrasomy and pentasomy X. Includes links to clinical research trials, latest news, support groups, photos, stories, and information on an annual retreat.

Unique: Rare Chromosome Disorder Support Group
Website for information, support, and awareness of families of children with rare chromosome disorders, including sex chromosome aneuploidies. Membership is free.

Genetic Alliance: Advocacy, Education & Empowerment
General resources, glossary, and tools for understanding genetic disease.

Google Search for Tetrasomy X

References and Sources

Linden MG, Bender BG, and Robinsons A (1995). Sex chromosome tetrasomy and pentasomy, Pediatrics, 96:4 Pt 1, p 672-82.