XYY

What is XYY (Jacobs syndrome)?

XYY, also known as Jacobs syndrome, is a condition that causes above average height and learning challenges in affected males. It is caused by a difference in the number of sex chromosomes. Females typically have two X chromosomes, while males typically have one X and one Y chromosome. XYY is caused when a male has two copies of the Y chromosome in the cells of the body instead of one. The symptoms seen in XYY are a result of this extra material impacting the growth and development of an affected individual.

XYY syndrome can be associated with an increased risk of learning disabilities and delayed speech and language skills. Delayed development of motor skills, weak muscle tone, and behavioral and emotional difficulties are also possible. A small percentage of males with XYY syndrome are diagnosed with autism spectrum disorders, which are developmental conditions that affect communication and social interaction. Most males with XYY syndrome have normal sexual development and are fertile.

Each person with XYY syndrome is unique and the severity of symptoms varies greatly among individuals.

How common is XYY?

The incidence of XYY is 1 in 1,000 male births. There is usually no family history of the condition.

How is XYY treated?

There is no cure for XYY. Treatment for the condition is directed at managing the specific symptoms an individual has. Common interventions may include physical, developmental, occupational, or speech therapy for developmental or speech problems. Additionally, a pediatric psychologist or group therapy may be helpful for social difficulties.

What is the prognosis for an individual with XYY?

Individuals with XYY will typically have normal or near-normal lifespans.