What Is XYY Syndrome? Symptoms, Causes, Diagnosis, Treatment, and Prevention

XYY syndrome is a genetic condition that occurs when a male is born with an extra Y chromosome.

Instead of having one X and one Y sex chromosome, those with XYY syndrome have one X and two Y chromosomes.

Sex chromosome abnormalities like XYY syndrome are some of the most common chromosome abnormalities. (1,2)

Other names for the condition are 47,XYY syndrome, Jacobs syndrome, XYY karyotype, or YY syndrome. (3)

Newborns with XYY syndrome don’t display noticeable physical characteristics.

As children get older, physical symptoms of XYY syndrome can include: (1,2)

• Taller height
• Slightly larger head size
• Widely spaced eyes
• Weak muscle tone
• Fifth fingers that curve inward
• Large teeth
• Flat feet
• Increased belly fat
• Scoliosis
• Hand tremors or motor tics
• Asthma
• Delayed development of motor skills, such as sitting and walking

The first five above are the most common physical exam findings. However, because these characteristics can fall within the normal range for males, often those with XYY syndrome do not get diagnosed.

Developmental signs of the syndrome may include: (2,4)

• Delayed development of speech and language skills
• Attention deficit disorder/attention deficit hyperactivity disorder (ADD/ADHD)
• Depression
• Anxiety
• Autism spectrum disorder

Being male is the biggest risk factor.

Most cases of XYY syndrome are not inherited, and the syndrome occurs randomly in pregnancies of women from all ages and ethnic backgrounds.

People normally have 46 chromosomes in each cell.

Two of the 46 chromosomes, known as X and Y, are called sex chromosomes because they help determine the biological sex of the individual.

Females normally have two X chromosomes, while males have one X chromosome and one Y chromosome.

However, boys born with XYY syndrome have an extra Y chromosome in each cell of their body.

Jacobs syndrome is not genetic, though the exact reasons for the chromosomal misfire are unclear. It appears to be somewhat random, resulting from flaws in the cell division process of the Y chromosome prior to conception or during the development of the embryo after conception. (1)

Since there is often no medical reason to test for XYY syndrome, the diagnosis is commonly never made.

With that said, a diagnosis can be made before birth while a baby is still in the mother’s womb with amniocentesis, which involves gathering a sample of fluid that surrounds the fetus or through chorionic villus sampling (CVS), the removal of tissue samples from a portion of the placenta. (3)

These tests can reveal if an extra Y chromosome is present.

If prenatal diagnosis is not done, a physician can diagnose XYY syndrome on a person by performing a clinical evaluation, patient history, and specialized tests, such as a karyotype, which is the most common test, to detect the presence of an extra Y chromosome. (3)

Boys may also be diagnosed because of learning problems, developmental delay, or behavioral issues. (3)

Prognosis of XYY Syndrome

Those with XYY can expect to have a good long-term outlook. Boys can do well in school and in building relationships, while adults with the syndrome can have successful careers and families. (4)

There is no treatment for XYY syndrome, and it is a lifelong condition. However, boys and men with XYY can live normal lives and seek help for particular symptoms, such as learning or developmental delays through speech therapy, occupational therapy, or other assistance. (4)

There is no treatment for XYY syndrome. However, medication and therapies can help with symptoms and complications of the condition.

Medication Options

While medication cannot treat XYY syndrome, some medications can be used to treat conditions related to the syndrome. For instance, medication for acne or ADD/ADHD can help as they would in people who have those conditions but do not have XYY syndrome. (3)

Alternative and Complementary Therapies

A person with XYY syndrome can get help with any learning or developmental delays through speech therapy, occupational therapy, or other assistance. Therapy can also help with ADD/ADHD, social interactions, and other behavioral problems. (3)

Prevention of XYY Syndrome

Because XYY syndrome is not inherited, and the syndrome occurs randomly in pregnancies of women from all ages and ethnic backgrounds, it cannot be prevented. (4)

XYY syndrome may increase the risk of the following: (4)

• Scoliosis
• Weak muscle tone
• Hand tremors or motor tics
• Delayed development of motor skills, such as sitting and walking
• Delayed development of speech and language skills
• ADD/ADHD
• Depression and anxiety

The condition occurs in about 1 in 1,000 live births, with 5 to 10 boys with XYY syndrome born daily in the United States. (2)

XYY syndrome is not inherited and occurs randomly in pregnancies of women from all ages and ethnic backgrounds.

Complications of the condition include physical, such as infertility and sexual function issues, osteoporosis, heart and blood vessel disease, breast cancer, and lung disease, as well as developmental challenges, including ADD/ADHD. (1,2,4)

The closest disorders associated with XYY syndrome are other conditions that include sex chromosome abnormalities, such as Klinefelter syndrome, which is a group of chromosomal disorders in males in which one or more extra X chromosomes are present. (3)

Other disorders that share similar symptoms to XYY syndrome, but have different molecular causes, include:

• Sotos syndrome, a genetic disorder characterized by excessive growth before and after birth
• Marfan syndrome, a genetic disorder that affects connective tissue (3)

Reliable health resources can be helpful for finding information and support for XYY syndrome. Many organizations provide educational materials and can help you find doctors who specialize in symptoms related to the syndrome. There are also online communities that offer support as well as practical advice and tips. Here are two we recommend.

Genetic and Rare Diseases Information Center (GARD)

GARD provides current, reliable, and easy-to-understand information about rare or genetic diseases in English or Spanish.

Unique

Unique supports, informs, and connects with anyone affected by a rare chromosome disorder or an autosomal dominant single gene disorder.