What Is XYY Syndrome?
XYY Syndrome is a genetic
condition that occurs when a male’s genes have an extra Y chromosome. Females
typically have two X chromosomes (XX). Males typically have one X chromosome
and one Y chromosome (XY). Males with this genetic condition have an extra copy
of the Y chromosome in each of their cells (XYY).
Most people have 46 chromosomes in each cell. Males with XYY syndrome
have 47 because of the extra copy of the Y chromosome. However, sometimes this
mutation is only present in some cells. According to the National Institutes of
Health, XYY syndrome occurs in 1 out of every 1,000 boys (Genetics Home
XYY Syndrome is also sometimes called Jacob’s Syndrome, XYY
Karyotype, or YY Syndrome.
Males with XYY Syndrome live typical lives for the most part. Some
males with XYY Syndrome may be taller than average and face learning difficulties
or speech problems. They may also grow up with minor physical differences, such
as weaker muscles and bones and delayed puberty. When they are older, men with
the syndrome may face fertility issues and complications related to low
testosterone levels. Besides these complications, however, males with XYY
syndrome do not usually have any distinguishing physical features or
complications, and have normal sexual development.
What Causes XYY Syndrome?
XYY Syndrome is the result of a random mix-up during the creation of a
male’s genetic code. Most cases of XYY Syndrome are not inherited, and researchers
do not believe that there is any genetic predisposition to it. Men with XYY
Syndrome are not more or less likely to pass the syndrome on to their male
children. Because the error is random and occurs at different times during cell
division, a male with XYY syndrome may have some cells that are not
affected—some cells may have XY chromosomes while others have XYY chromosomes.
Who Is at Risk for XYY Syndrome?
XYY Syndrome is not inherited. All males are at the same risk for the
What Are the Symptoms of XYY Syndrome?
The signs and symptoms of XYY Syndrome differ from patient to patient
and age to age.
The following signs may be an indication that a baby boy has XYY
- hypotonia, or weak muscle tone
- delayed motor skill development, such as walking
- delayed or difficult speech
- not easily excitable (is normally quiet and calm)
- undescended testicles at birth
The following signs
may be an indication that a young boy or teenager has XYY Syndrome:
- an autism diagnosis
- an inability to grow facial or body hair
- attention difficulties
- delayed motor skill development, such as writing
- delayed or difficult speech
- delayed or absent puberty
- emotional or behavioral issues
- gynecomastia, or enlarged breast tissue
- hand trembling or involuntary muscle movements
- hypogonadism, or low testosterone levels
- hypotonia, or weak muscle tone
- learning disabilities
- low energy levels
- small penis
- small, undersized testicles
- taller than average height
- weak bones
In addition to the signs above, the following signs may be an
indication that an adult male has XYY Syndrome:
- decreased sex drive
- decreased sperm counts
How Is XYY Syndrome Diagnosed?
XYY Syndrome may remain undiscovered and undiagnosed until a male
reaches adulthood. That’s when fertility problems, such decreased sperm counts,
alert doctors to a possible undiagnosed condition.
Two tests may be used to diagnose XYY Syndrome:
testing. Your doctor may request a Sex Hormone-Binding Globulin (SHBG) test
to check your testosterone levels. They may request a total testosterone test,
too. Both tests analyze blood or urine samples to determine if a man’s
testosterone levels are low, a possible indication that he has a problem. If
the testosterone levels are low, your doctor may request additional tests to
determine the cause.
analysis. Genetic disorders, such as XYY Syndrome, can be diagnosed with a chromosome
analysis. If your doctor is unable to find an explanation for symptoms that may
indicate XYY Syndrome, you may be requested to undergo a chromosome analysis to
check for XYY Syndrome.
How Is XYY Syndrome Treated?
The XYY Syndrome cannot be cured, but treatments can help reduce
symptoms and the effects caused by it, especially if it is discovered and
diagnosed early. Patients can work with health care providers to address any
symptoms they may have, such as speech disabilities, hormonal imbalances, and
learning problems. As a man gets older, he may want to work with a reproductive
specialist to address any infertility concerns.
The following treatment options may be used to address some of the most
common effects of XYY Syndrome:
replacement therapy. Males who do not produce adequate testosterone may
need hormone replacement therapy as they grow older. Hormone therapy can help
teenage boys undergo normal puberty. It can also help older men improve their
sexual drive and energy levels, or increase bone strength and improve muscle
mass. This therapy is typically given as an injection, but some patients may be
able to use a rub-on gel.
treatment. Men with XYY Syndrome may have low sperm counts and difficulty
conceiving a child. Testosterone replacement therapy will not increase
fertility, but it can help increase sexual drive. Men wishing to have a child
may need to see a fertility specialist to discuss options, such as intracytoplasmic sperm injections (ICSI).
During this procedure, sperm is removed from a man’s testicle and then injected
directly into a woman’s egg before it is planted back inside of her.
Gynecomastia. Men with
excess breast tissue as a result of XYY Syndrome may want plastic surgery to
remove the breast tissue.
therapy. Patients with XYY Syndrome may experience speech or motor skill
disabilities as a result of the condition. Healthcare professionals can help
treat these and provide plans for future improvements.
or occupational therapy. Some younger patients with XYY Syndrome experience
delayed motor skill development or difficulty with muscle strength. Physical
therapists and occupational therapists can help patients overcome these
therapy. Some patients with XYY Syndrome experience learning disabilities.
Talk with your child’s teacher, principal, and special education coordinators
to arrange a schedule that is best suited to your child’s needs. Outside tutors
and educational instruction may be necessary.
What Is to Be Expected in the Long Term?
Men with XYY Syndrome can—and very often do—live completely normal
lives with the condition. XYY Syndrome can remain undiagnosed throughout a
man’s lifetime. If it is diagnosed, however, individuals with XYY Syndrome can
find the help they might need.