XYY Syndrome

Syndrome is a rare genetic disorder which affects males due to an extra Y chromosome.
Healthy males have 46 chromosomes including one X and one Y chromosome. Men
with XYY syndrome have 47 chromosomes, two of which are Y chromosomes. It
is not known why the extra Y chromosome occurs. The disorder is present at
birth and is estimated to occur in one out of every one thousand live births.
In very rare instances, the syndrome has been passed from father to son, but
in most cases heredity cannot be established.

The characteristics of
XYY syndrome are often very subtle and do not indicate and serious chromosomal
disorder. Therefore, males with this condition are frequently undiagnosed
or misdiagnosed. The primary symptoms include tall or very tall height which
becomes evident at the age of five or six, and severe cystic acne during adolescence.

than average intelligence and/or behavioral problems, such as an explosive
temper, aggressive or defiant actions, or sometimes antisocial behavior are
other symptoms. Some individuals with this disorder may also have language
difficulties or psychosexual problems. XYY Syndrome is often undiagnosed until
tests for other medical reasons are performed. Other than being unusually
tall and/or having behavioral problems, in many cases, these boys or men appear

Physical characteristics of XYY Syndrome may include an exceptionally
long head with a slightly protrusive forehead, long hands and feet, long ears,
mild indentation of the breastbone, and/or large teeth. Poor chest and shoulder
muscle development is also common. Even though males with this syndrome are
large, they tend to be weak and uncoordinated. Some may have a fine intentional
tremor, such as shaking hands when the try to drink a glass of water. Occasionally,
a bony formation across the joints in the two bones of the forearm resulting
in the stiffening of the affected joints may occur. Other occasional symptoms
are undescended testicles, a small penis, or an opening located on the underside
of the penis.

For a long time it was thought that XYY Syndrome individuals
had aggressive tendencies often associated with criminal behavior due to the
extra Y chromosome. Epidemiological studies suggest that one out of every
35 institutionalized male juvenile delinquents has XYY Syndrome. However,
it is now believed by some researchers that this behavior is not due to the
extra Y chromosome, but rather to the lower than average intelligence and education
levels of these men. More research is needed to understand the role of this
chromosomal abnormality on behavior.