47,XYY Syndrome (Jacobs Syndrome)

What is 47,XYY syndrome (Jacobs syndrome)?

47,XYY syndrome (or what used to be called Jacobs syndrome) is a condition in which people assigned male at birth (AMAB) have an additional Y chromosome in their genetic code.

Most people AMAB have 46 chromosomes (packages of DNA). This includes one copy of an X chromosome and one copy of a Y chromosome (46,XY). People with 47,XYY have a total of 47 chromosomes (47,XYY). Healthcare providers may call this condition 47,XYY, or XYY for short.

47,XYY is a congenital difference. That means you’re born with it. But the symptoms of this difference are mild enough that only around 10% of cases are diagnosed. 47,XYY affects each person differently.

Most people with 47,XYY:

• Have typical production of testosterone
• Have typical male sexual development during puberty
• Produce sperm and have typical fertility

How common is 47,XYY (Jacobs syndrome)?

47,XXY is relatively rare. It affects about 1 out of 1,000 newborns assigned male at birth.

What are the symptoms of 47,XYY?

There are no guaranteed signs or symptoms of 47,XYY. But it’s associated with certain symptoms and physical features. Your child may have none or any combination of these.

People with 47,XYY syndrome have an increased chance of:

• Anxiety
• Asthma
• Attention-deficit/hyperactivity disorder (ADHD)
• Autism spectrum disorder (ASD)
• Behavioral issues, like excessive aggression and impulsivity
• Delayed development of fine motor skills (like writing and using scissors)
• Delayed development of speech and language skills
• Depression
• Enlarged testicles
• Hand tremors or other involuntary movements
• Learning disabilities
• Seizures

Physical traits that may accompany 47,XYY include:

• Tall stature — it’s common to be 6’3” (1.88m) and taller at final height
• A large head (macrocephaly)
• Widely spaced eyes (orbital hypertelorism)
• Weak muscle tone (hypotonia)
• Fifth fingers (pinkies) that curve inward (clinodactyly)
• Larger than typical teeth (macrodontia)
• Underbite
• Flat feet (pes planus)
• Abnormal side-to-side curvature of the spine (scoliosis)

Some — not all — people with 47,XYY may have male infertility due to oligospermia or sperm abnormalities.

What causes 47,XYY?

47,XYY happens when there’s an extra Y chromosome in your genetic code. This change happens before birth and can occur in one of two ways:

• A sperm cell carries an extra Y chromosome and fertilizes an egg at conception. This is the most common form.
• Cells divide atypically during early fetal development — embryonic development, specifically. Healthcare providers call this 46,XY/47,XYY mosaicism. People with this form only have an extra Y chromosome in some of their cells. It’s less common.

47,XYY isn’t an inherited condition. The extra Y chromosome most often results randomly during the non-birthing parent’s sperm production. A sperm with two Y chromosomes fertilizes an egg, which has an X chromosome, resulting in the syndrome.

Researchers don’t know why these chromosomal changes happen. They seem to happen randomly. It’s also unclear why an extra copy of the Y chromosome is associated with certain conditions and physical features.

How is 47,XYY diagnosed?

There are two ways a 47,XYY diagnosis may happen:

• Prebirth. If you get noninvasive prenatal testing (NIPT), a CVS or an amniocentesis during pregnancy, it may detect chromosomal differences in the fetus.
• After birth. Genetic testing can detect 47,XYY.

Researchers estimate that 85% to 90% of people with 47,XYY never get a diagnosis. This is because the difference often doesn’t cause obvious symptoms or issues. And the conditions that are associated with it are wide-ranging and have other causes. If someone with 47,XYY does receive a diagnosis, it’s often delayed. The average age of diagnosis is about 17 years.

What’s the treatment for 47,XYY ?

There’s no direct treatment or cure for 47,XYY. Medical support and other interventions are mainly for any conditions that may develop.

For example:

• Speech therapy can help with speech and language developmental delays.
• Physical therapy and occupational therapy can help with low muscle tone and motor skill issues.
• Special educational resources (like an individualized education plan, or IEP) can help with learning disabilities.
• Psychotherapy (talk therapy) can help with mental health conditions and behavioral issues.
• Medications may help physical conditions like asthma and seizures.
• Orthodontic and dental procedures can address issues like tooth crowding and underbite.
• In vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) can help fertility concerns.

Can 47,XYY be prevented?

There’s nothing you can do to prevent it. The extra Y chromosome happens randomly.

What can I expect if my baby has 47,XYY?

If you found out your baby will have this difference through prenatal testing, you may be overwhelmed. Know that the syndrome affects each person differently. Many people have mild, few or no issues because of it. There’s no way to predict how it’ll affect your child. But the more information you have about the increased risks for your child, the more prepared you can be.

Your child’s healthcare provider will likely recommend a “wait and see” approach. They’ll give you information on signs and symptoms to look out for diagnoses like developmental delays, ADHD and learning disabilities.

As with any child, being attentive to their health — physical, mental, emotional and behavioral — is key. If you notice differences in your child, reach out to their provider for advice. The sooner your child can receive interventions or treatment, the better.

In general, children with 47,XYY live typical lives. They may occasionally need extra support or medical care in certain areas, but so do many children without 47,XYY.

What can I expect if I have 47,XYY?

If you found out you have 47,XYY as a teen or adult, you may be shocked or perplexed. It’s natural to have a lot of questions. Know that your healthcare provider will give you information about the syndrome. You may discover that the syndrome “explains” a lot of your life experiences — or it may just be another detail about you.

Consider finding a support group or a network of other people living with 47,XYY. You can learn more about it and perhaps feel less alone in the diagnosis.

It’s important to note that having 47,XYY doesn’t increase the likelihood of having a biological child with it. 47,XYY isn’t an inherited condition. Some people with 47,XYY experience fertility issues, but most don’t. Be sure to reach out to your provider if this is a concern for you.

What is the life expectancy of a person with 47,XYY?

One study showed that the lifespan of a person with 47,XYY may be about 10 years less than that of other people AMAB. Researchers think this may be due to the conditions and situations that can accompany the difference, like asthma, seizures and behavioral issues (like impulse control).

Staying on top of your health may help increase your life expectancy. Be sure to see your healthcare provider regularly.