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

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XYY syndrome is a rare chromosomal health condition, which is a type of genetic disorder. It is also known as XYY karyotype, YY syndrome, or Jacob’s syndrome. It often goes undiagnosed because the symptoms are mild. But it increases your likelihood of having developmental delays or behavioral issues at a young age. So if you or your child has a history of speech delay, developmental issues, or learning disabilities, XYY syndrome might be the cause. With early treatment and support, males with XYY syndrome can lead healthy, productive lives. If you suspect that you or your child may have this disorder, continue reading for more information.

What is XYY Syndrome?

XYY syndrome is a disorder of the chromosomes. Chromosomes are the structures that contain all your genetic material, where males end up with an additional Y chromosome instead of just XY. About 1 in 1000 males are born with this disorder, and about 200,000 people in the US live with it. Many people with this disorder are asymptomatic, apart from a taller than average stature. In addition, they often have normal testosterone levels, sexual development, and fertility. Since people are usually asymptomatic or have only mild symptoms, they can go undiagnosed their entire lives or get diagnosed later in life.

Causes of XYY Syndrome

Males usually have X and Y chromosomes as their sex chromosomes. When you have XYY syndrome, an error in cell division occurs in male reproductive cells, called sperm cells. This results in an extra Y chromosome and 47 chromosomes total. XYY syndrome is not inherited, meaning it is not passed down from parents to kids and happens randomly.

Signs & Symptoms

The symptoms of XYY syndrome are normally so mild that 9 out of 10 people with this disorder never seek care for it or get diagnosed. The most frequent symptoms and signs include: 

  • Learning disabilities
  • Behavioral disturbances
  • Delayed speech development
  • Taller than average male

Other XYY syndrome characteristics may include:

  • Hand tremors
  • Large head
  • Large teeth or underbite
  • Flat feet
  • Pinky fingers that curl inward
  • Widely spaced eyes
  • Abnormal curvature of the spine
  • Low muscle tone is when the muscles appear weak and floppy
  • Infertility

Risk Factors

If you have XYY syndrome, you have a higher risk of:

Because the symptoms of XYY syndrome are similar to other conditions, it’s important to consult with your doctor to get the right diagnosis.

Diagnostic Tests

Doctors can diagnose you or your child with XYY syndrome before or after birth. Before birth, doctors can diagnose your unborn child with the disorder by using noninvasive prenatal testing and a karyotype test. 

Noninvasive prenatal testing: Noninvasive prenatal testing (NIPT) tests your baby’s DNA for genetic abnormalities. Your doctor can get a sample of your baby’s DNA by taking a sample of your blood, cells from the placenta, or some of the amniotic fluid surrounding your baby in the womb, to help diagnose your baby with XYY syndrome. If this test comes back positive, another test will confirm the diagnosis.

Karyotype test: A karyotype test is another genetic test that shows the size, shape, and number of chromosomes your baby has in their cells. Like with NIPT, your doctor will get a sample of your baby’s DNA by taking a sample of your blood, cells from the placenta, or some of the fluid surrounding your baby in the womb. If your baby has XYY syndrome, a karyotype test will show that he has an extra Y chromosome. If you’re seeking a diagnosis as a teen or adult, your doctor may take a sample of your blood to perform a karyotype test.

Treatments for XYY Syndrome

There is no cure for XYY syndrome, but several treatments, especially treatments given early on, can help you with some of your symptoms. The prognosis for XYY syndrome is very good, and people with this syndrome go on to lead long and happy lives. XYY syndrome treatments include:

  • Regular doctor visits: Your doctor can monitor you or your child for signs of health problems, developmental delays, or social and language disabilities and address these issues promptly.
  • Educational support services: Many people with XYY syndrome have learning disabilities. If you have this disorder and have learning disabilities, support services can help you do better with your schoolwork.
  • Early intervention services: People with XYY syndrome often have developmental problems, and it is important to address them as soon as they are noticed. Speech, occupational, physical, or developmental therapy can help you manage these problems. 
  • Counseling: If you or someone in your family has XYY syndrome, it may be helpful for you and your family members to receive counseling to understand how to best support your loved one

Next Steps

Talk to your doctor if you notice that your child has developmental issues or if you have a history of symptoms consistent with XYY syndrome and suspect you have this disorder. There is no way to prevent XYY syndrome because it is genetic. However, early interventions can improve outcomes for those affected by it. Several organizations can give you more information about this disorder, some of which are listed here. Feel free to ask your doctor for more information if you have more questions about XYY syndrome.

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Resource Links:

  1. “47, XYY Syndrome” via MedlinePlus
  2. “47, XYY syndrome” via Rare Diseases NIH
  3. “Karyotype Genetic Test” via MedlinePlus
  4. “Microarray Analysis Test” via Nationwide Children’s
  5. “What is noninvasive prenatal testing (NIPT) and what disorders can it screen for?” via MedlinePlus
  6. “XYY syndrome” via KidsHealth
  7. “XYY Syndrome” via National Organization for Rare Disorders
  8. “ Jacobs Syndrome” via StatPearls