Trisomy X a.k.a. XXX Syndrome

What is trisomy X?

Trisomy X, also referred to as XXX Syndrome, is a chromosomal disorder that only affects females and is characterized by the presence of an extra X chromosome. Chromosomes carry the genetic characteristics of individuals, and are located in the nucleus of all body cells. Normally, females have two X chromosomes, but those with trisomy X carry three X chromosomes in the nuclei. Trisomy X is estimated to occur in one in 1,000 female births. However, since some females with the disorder may have mild or no symptoms, they may not be diagnosed, which means the disorder is likely underdiagnosed.

What are the symptoms of trisomy X?

Symptoms and physical features can vary significantly from one person to another. Some individuals may not have any symptoms at all and will go undiagnosed. Every affected individual may not have every symptom listed below, but the possible symptoms include:

• Taller than average height
• Language-based learning disabilities, including dyslexia, reading comprehension deficits, and/or fluency issues
• Developmental delay of motor skills, like sitting up and walking
• Developmental delay of speech skills
• Developmental dyspraxia
• Mild facial abnormalities
  • Widely spaced eyes
  • Unusually small head circumference
  • Vertical skin folds that cover the inner corners of the eyes
• Low muscle tone
• Abnormal bending or curving of pinkies toward the ring fingers
• Behavior and emotional problems
• ADHD
• Some may experience abnormal development of the ovaries, delayed or early onset puberty, fertility problems, and/or premature ovarian failure
• Seizures
• Kidney abnormalities

What causes trisomy X?

Trisomy X occurs randomly due to errors during the division of reproductive cells in one of a person’s parents. Humans have 23 pairs of chromosomes, so 46 chromosomes in total, with the 23^rd pair consisting of two X chromosomes for females. However, females with trisomy X have 47 chromosomes, three of which are X chromosomes. While trisomy X is a genetic disorder, it isn’t inherited. Females get the extra X chromosome because of errors during the normal division of reproductive cells in one of the parents. These errors occur randomly. Studies have shown that the risk of error increases with advanced paternal age, but in most children, the additional X chromosome comes from the mother.

How is trisomy X diagnosed?

Trisomy X is diagnosed using the following procedures:

• Identification of characteristic neurodevelopmental, behavioral, or learning disabilities
• Clinical evaluation
• Detailed family history
• Chromosomal analysis performed on blood samples
• Before birth, through chromosomal analysis performed through amniocentesis or chorionic villus sampling (CVS)

What are the treatments for trisomy X?

Trisomy X treatment strategies are specialized depending on the age and needs of the patient. Early intervention and therapy is highly recommended for infants and children diagnosed. Treatment includes, but is not limited to:

• Speech therapy
• Occupational therapy
• Physical therapy
• Developmental therapy and counseling
• Kidney and heart evaluations to make sure there are no associated abnormalities
• Genetic counseling

Where can I find out more about trisomy X?

• National Organization for Rare Disorders (NORD)
• Mayo Clinic
• NIH