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47, XYY syndrome

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Other Names: YY syndrome; XYY syndrome; XYY Karyotype; Jacobs syndrome; 47,XYY syndrome; Disomy Y; Double Y; Double Y syndrome; Y disomy

47,XYY syndrome is characterized by an extra copy of the Y chromosome in each of a male's cells. Although many males with this condition are taller than average, the chromosomal change sometimes causes no unusual physical features. Most males with 47,XYY syndrome have normal production of the male sex hormone testosterone and normal sexual development, and they are usually able to father children.

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Meiosis II Non Disjunction.jpg
XYY Syndrome DNA.jpg


This condition occurs in about 1 in 1,000 newborn boys. Five to 10 boys with 47,XYY syndrome are born in the United States each day. Many affected males are never diagnosed or not diagnosed until later in life.


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) in each cell.

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. It is unclear why an extra copy of the Y chromosome is associated with tall stature, learning problems, and other features in some boys and men.

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.


Most cases of 47,XYY syndrome are not inherited. The chromosomal change usually occurs as a random event during the formation of sperm cells. An error in cell division called nondisjunction can result in sperm cells with an extra copy of the Y chromosome. If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have an extra Y chromosome in each of the body's cells.

46,XY/47,XYY mosaicism is also not inherited. It occurs as a random event during cell division in early embryonic development. As a result, some of an affected person's cells have one X chromosome and one Y chromosome (46,XY), and other cells have one X chromosome and two Y chromosomes (47,XYY).

Signs and symptoms

The signs and symptoms of 47, XYY syndrome can range from barely noticeable to more severe. It is thought that some males with 47, XYY syndrome may never be diagnosed because the signs and symptoms may not be noticeable. For other males, signs and symptoms such as low muscle tone (hypotonia) and/or speech delay may begin in late infancy or early childhood. Some boys with 47, XYY syndrome may have difficulty in certain subjects in school such as reading and writing. However, boys with this syndrome do not typically have intellectual disability.

Other signs and symptoms of 47, XYY syndrome may include asthma, dental problems, and acne. Boys with the syndrome don’t typically have physical features different from most people, but they may be taller than expected. These boys are not expected to have differences in the appearance of the sex organs (genitalia).

Some males with 47, XYY syndrome have behavioral differences such as autism spectrum disorder (usually on the milder end) or attention deficit hyperactivity disorder (ADHD). Boys with 47, XYY syndrome are also at an increased risk to have anxiety or mood disorders.

Most boys with 47, XYY syndrome go through normal sexual development, and fertility is expected to be normal. However, some boys with the syndrome may develop testicular failure (when the testes can’t produce sperm or testosterone), which can lead to problems with fertility.

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. 80%-99% of people have these symptoms

  • Delayed speech and language development(Deficiency of speech development)
  • Low-set ears(Low set ears)
  • Malar flattening(Zygomatic flattening)
  • Motor delay
  • Tall stature(Increased body height)

30%-79% of people have these symptoms

  • Asthma
  • Attention deficit hyperactivity disorder(Attention deficit)
  • Congenital stationary night blindness(Night blindness since birth)
  • Finger clinodactyly
  • Hypertelorism(Wide-set eyes)
  • Impaired social interactions(Impaired social interaction)
  • Impulsivity(Impulsive)
  • Intellectual disability(Mental deficiency)
  • Macrocephaly(Increased size of skull)
  • Neonatal hypotonia(Low muscle tone, in neonatal onset)
  • Specific learning disability


47, XYY syndrome may be suspected when a doctor observes signs and symptoms that can be associated with the syndrome such as low muscle tone (hypotonia), speech delay, or learning problems in school. A doctor may then order testing to see if there is a genetic explanation for the signs and symptoms. Tests that may be ordered include: Karyotype: a test that is used to view all the chromosomes in a cell Chromosomal microarray: a test that looks for extra or missing chromosomes or pieces of chromosomes In some cases, 47, XYY syndrome may be suspected prenatally based on routine screening tests. A diagnosis can be confirmed with prenatal tests such as an amniocentesis or chorionic villus sampling (CVS). It is thought that some people who have 47, XYY syndrome are never diagnosed because they do not have severe signs or symptoms of the syndrome.


The signs and symptoms of 47, XYY syndrome can be managed with a variety of therapies. Occupational therapy may be recommended for infants and young boys who have low muscle tone (hypotonia), and speech therapy may be recommended for boys who have speech delay.

Boys with 47, XYY syndrome may be in special education at school, or they may have extra help in some classes. Other management options for boys with 47, XYY syndrome may include behavioral therapy or medications for boys with attention deficit hyperactivity disorder (ADHD) or behavioral problems. If autism spectrum disorder is present, applied behavioral analysis (ABA) therapy may be recommended. In some cases, hormonal therapy may be used.


The long-term outlook for people with 47, XYY is typically good. Boys with this syndrome can do well both in school and in building social relationships. Men with 47, XYY syndrome can also have successful careers and families of their own.Therapies and other management for the syndrome can be important in allowing affected males to reach their full potentials.

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