XYY syndrome

Nature of the Genetic Difficulty

Most cases of 47,XYY syndrome are not inherited. People normally have 46 chromosomes in each cell. Two of the 46 chromosomes, known as X and Y, are called sex chromosomes because they help determine whether a person will develop male or female sex characteristics. Females typically have two X chromosomes (46,XX), and males have one X chromosome and one Y chromosome (46,XY). 47,XYY syndrome is caused by the presence of an extra copy of the Y chromosome in each of a male's cells. As a result of the extra Y chromosome, each cell has a total of 47 chromosomes instead of the usual 46. Some males with 47,XYY syndrome have an extra Y chromosome in only some of their cells. This phenomenon is called 46,XY/47,XYY mosaicism.

Basis Facts of Disease

Just Some Facts:
Extra Y chromosome at birth
Affects about 1 in 1000 male births
IQ on average 10 to 15 points lower than siblings
Can develop extreme acne
Can grow an average of extra 3 inches of growth
Can delay development of speech and language skills
Can lack of complete motor skills hand tremors
Can experience emotional difficulties


Males will be generally taller by about 3 inches or 7 cm above expected final height. Severe acne was noted in a very few early case reports. Testosterone levels (prenatally and postnatally) are normal in 47,XYY males. Most 47,XYY males have normal sexual development and usually have normal fertility. 47,XYY syndrome is associated with an increased risk of learning disabilities and delayed development of speech and language skills. Delayed development of motor skills (such as sitting and walking), weak muscle tone (hypotonia), hand tremors or other involuntary movements (motor tics), and behavioral and emotional difficulties are also possible. These characteristics vary widely among affected boys and men.

Sources Cited