What is tetra x syndrome?

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Tetrasomy X, also know as Tetra X syndrome or XXXX syndrome, is an extremely rare condition that only affects females. This chromosomal disorder, first described in 1961, affects about 100 known females worldwide, although many more remain undiagnosed.

For every female living with Tetra X the symptoms and severity are as unique as the individual affected. Despite the little information available about the condition, early intervention and special programs can help many overcome Tetra X.


Everyone is born with 46 chromosomes, the last ones being the sex chromosomes. Males have XY sex chromosomes while females have XX. Girls born with Tetra X syndrome have two extra X chromosomes giving them a total of four X chromosomes. Instead of 46 chromosomes total, they have 48. According the Rare Chromosomal Disorder Support Group Unique, "girls with Tetrasomy X have inherited either three X chromosomes from their mother and a single X chromosome from their father or all four X chromosomes from their mother." This occurs from mistakes made during cell division in the mother's eggs. In even rarer cases, the mistake happens in cell division after conception. Tetra X syndrome is a genetic anomaly that cannot be prevented or predicted.

Physical Symptoms

Babies born with Tetra X syndrome have growth rates that range from short to normal to tall, just as in the general population. As they grow, however, they tend to be thin and tall. Some children will have unusual facial features, although most do not. Many physical developmental baby milestones are delayed for those with Tetra X, including walking, which may not occur until closer to the age of 2 or later. Hypotonia, a weakness in the muscles, causes the physical delays in some cases. A significant portion of Tetra X girls also have heart conditions, joint problems and kidney and bladder abnormalities. Some may suffer from skeletal malformations, hearing loss and puberty irregularities.

Developmental Symptoms

Most with Tetra X syndrome will have a slight learning disability, although some individuals will test at a normal level of intelligence and have few if any learning difficulties. Speech delay is often the most obvious and first symptom. The average age of when a toddler with Tetra X syndrome starts to speak is around 3. With speech therapy, the prognoses for improved speech is excellent.


No cure or treatment exists specifically for the cause of Tetra X syndrome. Treatment involves support of the symptoms only. For hypotonia, physiotherapy and orthotic braces are used. Speech therapy started as soon as the delay is noted often helps the child speak normally later in life. Oestrogen treatment "induces breast development, stops longitudinal growth, and stimulates bone formation to prevent osteoporosis," according to Madison's Foundation. Other conditions such as those affecting the heart or renal system are treated on a case-by-case basis.


The rarity of this disorder unfortunately means that research is also almost nonexistent. Much of the information known about this genetic condition comes from informal surveys of parents whose children have been diagnosed with Tetra X syndrome. A blood test has been developed to test for the disorder. The probability of a mother having more than one child with Tetra X syndrome is highly unlikely, although consultation with a geneticist will help you understand your personal risk.