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What Is XYY Syndrome?

XYY syndrome is a genetic condition found in males only. About 1 in 1,000 boys have it.

Boys with XYY syndrome — also known as 47,XYY — might be taller than other boys. Other symptoms can include problems with spoken language and processing spoken words, coordination problems, weaker muscles, hand tremors, and behavioral problems.

Most boys with XYY syndrome can grow up healthy, have normal sexual development and fertility, and lead productive lives.

Symptoms can vary greatly among boys. Depending on which symptoms a boy has and how severe they are, doctors may recommend various treatments.

What Causes XYY Syndrome?

Boys who have XYY syndrome are born with it. It's called XYY because they have an extra Y in most or all their cells.

Usually, a person has 46 chromosomes in each cell, divided into 23 pairs, which includes two sex chromosomes. Half the chromosomes are inherited from the father and the other half from the mother. The chromosomes contain genes, which determine an individual's characteristics, such as eye color and height. Boys typically have one X chromosome and one Y chromosome, or XY, but boys with XYY syndrome have an extra Y chromosome, or XYY.

XYY syndrome is not caused by anything the parents did or did not do. The disorder is a random error in cell division. This error can happen before conception in the reproductive cells of the mother or the father, or early in the embryo's development.

When the extra chromosome is the result of incorrect cell division early in the embryo's development, a boy may have a mosaic form of XYY syndrome. This means some cells have an extra Y chromosome, but not all do. Boys with mosaic XYY syndrome usually have fewer symptoms.

What Are the Signs & Symptoms of XYY Syndrome?

Noticeable signs and symptoms of XYY syndrome can vary greatly. Some boys have no obvious signs, while others have mild symptoms. Occasionally, the disorder causes significant problems.

Boys with XYY syndrome may have some or all of these physical symptoms to some degree:

  • taller than average height
  • low muscle tone, or muscle weakness (called hypotonia)
  • very curved pinky finger (called clinodactyly)
  • widely spaced eyes (called hypertelorism)

Some boys also may have delayed development of their social, language, and learning skills. They also can have problems with reading and understanding math, and may have mild delays with coordination.

What Problems Can Happen?

Some boys with XYY syndrome may develop behavioral problems, such as ADHD, autism, temper tantrums, impulsivity, or defiant behavior. These problems might ease as they get older and reach adulthood. Otherwise, treatment can help manage these issues.

A small number of boys may have increased testicular size for their age, or have an increased risk for asthma and seizures.

How Is XYY Syndrome Diagnosed?

Many boys with XYY syndrome are healthy and have no obvious symptoms. So sometimes the condition isn't diagnosed or is found when a doctor checks for a different issue.

Often, XYY syndrome is found because parents talked with a doctor about concerns with their son's development. This can help boys receive a diagnosis early. Research has shown that early interventions and treatments are more effective.

To diagnosis XYY syndrome, doctors check a blood sample for the extra Y chromosome. Before birth, the condition may be found through (chromosomal analysis) or noninvasive prenatal testing (NIPT). NIPT is done on the fluid surrounding the fetus, tissue from the placenta, or the blood from the mother. After birth, doctors can make a diagnosis with a karyotype or with a from the baby.

How Is XYY Syndrome Treated?

There's no cure for XYY syndrome, but treatments can help with specific symptoms.

Finding services early is important and can greatly increase their ability to help boys live a healthier, more productive life. Options vary greatly depending on how old a boy is at the time of his diagnosis, whether he has noticeable symptoms, and the severity of those symptoms.

Treatments can include:

Regular doctor visits. At periodic visits, a doctor can monitor a boy's development for delays, social and language disabilities, or health problems and treat these promptly.

Educational support services. Educational support can teach boys ways to keep pace in school. Some might be eligible for an individualized educational program (IEP) or 504 education plan, which are designed to help children with special needs.

Early intervention services. It can be very helpful and often more effective for a boy to have speech, occupational, physical, or developmental therapy in the early months of life or as soon as concerns are found.

Speech therapy and physical therapy can improve a boy's speaking, reading, and writing skills and help increase strength and coordination. Occupational therapy and behavioral therapy can help them develop more confidence and interact better with other children.

Counseling. The whole family can benefit from counseling to better understand XYY syndrome and help a boy who has it to live a productive life.

Early inventions should be considered at infancy for physical therapy, at 15 months for speech delay, at 1st grade for reading and learning issues, and at 3rd grade for anxiety or depression.

What Else Should I Know?

Boys with XYY syndrome can develop speech, learning, or social challenges at a young age. This can make them more likely to have low self-esteem and lead to school or social problems.

If your son has trouble making friends or struggles in school, talk to your doctor or the principal or school counselor. Counseling and therapy can teach your son practical skills to help him make friends and feel more confident in school, and educational services can help him do well in school.

Talk to your doctor if you have any concerns about your son's physical and emotional development.

Despite physical differences and other problems, with the right medical care, early intervention, and ongoing support, a boy with XYY syndrome can lead a normal, healthy, and productive life.

Medically reviewed by: Judith L. Ross, MD
Date reviewed: August 2021