XXX Chromosome Disorder

Triple X syndrome

, also called trisomy X or 47, XXX, is a genetic disorder that affects about 1 in 1,000 females. Females normally have two X chromosomes in all cells — one X chromosome from each parent. In triple X syndrome, a female has three X chromosomes.

Many girls and women with triple X syndrome don’t experience symptoms or have only mild symptoms. In others, symptoms may be more apparent — possibly including developmental delays and learning disabilities. Seizures and kidney problems occur in a small number of girls and women with triple X syndrome.

Treatment for triple X syndrome depends on which symptoms, if any, are present and their severity.

Symptoms

Signs and symptoms can vary greatly among girls and women with triple X syndrome. Many experiences no noticeable effects or have only mild symptoms.

Being taller than the average height is the most typical physical feature. Most females with triple X syndrome experience normal sexual development and have the ability to become pregnant. Some girls and women with triple X syndrome have intelligence in the normal range, but possibly slightly lower when compared with siblings. Others may have intellectual disabilities and sometimes may have behavioural problems.

Occasionally, significant symptoms may occur, which vary among individuals. These signs and symptoms may show up as:

• Delayed development of speech and language skills, as well as motor skills, such as sitting up and walking
• Learning disabilities, such as difficulty with reading, understanding or math
• Behavioural problems, such as attention-deficit/hyperactivity disorder (ADHD) or symptoms of autism spectrum disorder
• Psychological problems, such as anxiety and depression
• Problems with fine and gross motor skills, memory, judgment and information processing

Sometimes females with triple X syndrome have these signs and symptoms:

• Vertical folds of skin that cover the inner corners of the eyes (epicanthal folds)
• Widely spaced eyes
• Curved pinky fingers
• Flat feet
• Breastbone with an inward bowed shape
• Weak muscle tone (hypotonia)
• Seizures
• Problems with the kidneys
• Ovaries that don’t work properly at a young age (premature ovarian failure)

Causes

Although triple X syndrome is genetic, it’s usually not inherited — it’s due to a random genetic error.

Normally, people have 46 chromosomes in each cell, organized into 23 pairs, including two sex chromosomes. One set of chromosomes is from the mother and the other set is from the father. These chromosomes contain genes, which carry instructions that determine everything from height to eye colour.

The pair of sex chromosomes — either XX or XY — determines a child’s sex. A mother can give the child only an X chromosome, but a father can pass on an X or a Y chromosome:

• If the child receives an X chromosome from the father, the XX pair makes the child genetically female.
• If the child receives a Y chromosome from the father, the XY pair means the child is genetically male.

Females with triple X syndrome have a third X chromosome from a random error in cell division. This error can happen before conception or early in the embryo’s development, resulting in one of these forms of triple X syndrome:

• Nondisjunction. In most cases, either the mother’s egg cell or the father’s sperm cell divides incorrectly, resulting in an extra X chromosome in the child. This random error is called nondisjunction, and all the cells in the child’s body will have the extra X chromosome.
• Mosaic. Occasionally, the extra chromosome results from an incorrect cell division caused by a random event early in the embryo’s development. If this is the case, the child has a mosaic form of triple X syndrome, and only some cells have the extra X chromosome. Females with the mosaic form may have less obvious symptoms.

Triple X syndrome is also called 47, XXX syndrome because the extra X chromosome results in 47 chromosomes in each cell instead of the usual 46.