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What is XXYY Syndrome?
48, XXYY is a sex chromosome variation that affects one in every 17,000 boys who are born.
XXYY Syndrome is the name attached to the cluster of symptoms that arise as a result of the 48, XXYY chromosome pattern.
48, XXYY is one of several types of sex chromosome variations, including those that are considered as variants of Klinefelter Syndrome, 47 XXY and XXXY, XXXXY, XY/XXY and another syndrome called XYY, all of which affect males. Similar female syndromes include Turner Syndrome (XO) and several variations with added X’s. There are important differences, between boys and men with 47,XXY and those with 48,XXYY and some authors have questioned whether 48, XXYY males should be included under the umbrella of Klinefelter Syndrome.
48, XXYY is not an Intersex condition or indication. Please read our notice on XXYY and Intersex Conditions.
 The incidence of 48,XXYY syndrome was originally estimated at 1/50,000 (Sorensen et al., 1978), but a recent report found the 48,XXYY karyotype in 1/17,000 males in a newborn screening (Nielsen et al., 1991).
 Grarnmatico et al., 1990 Males with XXYYhave two X and two Y sex chromosomes, instead of one each. XXYY is sometimes considered a variant of another syndrome called Klinefelter Syndrome, or 47 XXY. There are other types of sex chromosome anomalies such as XYY, XXXY, XXXXY, and variations in girls such as XO (Turner Syndrome), XXX, XXXX. and XXXXX.
Although there have been limited studies and research on XXYY, the fact that xxyy boys have many similar features is often not mentioned.
Characteristics of XXYY Syndrome
XXYY is often mistaken for other syndromes. The most common symptoms and characteristics that would be noticeable by parents, teachers, medical professionals and other treatment providers are:
- Developmental delays
- Speech impairment or delay
- Tall, considering family history
- Behavior outbursts & mood swings
- Learning disabilities
- Intellectual impairment
- ADD or ADHD symptoms
- Autism, autism spectrum, PDD-NOS
- Clinodactyly (Curved-in pinky fingers)
- Low muscle tone
- Flat feet/club feet
- Delayed sexual development
- Undescended testes
- Low or no testosterone
- Dental problems
- Leg ulcers
- Heart defects (ie VSD)
Cause and Rate of Occurrence
The cause of 48, XXYY is still not completely understood. Since extensive studies have not been conducted on the cause of 48, XXYY, there is currently very little information about whether or not there are environmental , herditary or other factors which can result in this chromosome pattern. There is no evidence that parents of one XXYY child are more likely to have other children with sex chromosomal variations. Sex chromosomal variations in general are actually quite common. The occurrence of 48, XXYY is 1 in 17,000 live male births. The occurence of Klinefelter Syndrome, XXY, is 1 in 500.
Diagnosing 48, XXYY
Diagnosing 48, XXYY requires a genetic test called a karyotype. The test is done by drawing blood and an analysis is done on the cells of the blood to determine the boy or man’s chromosomal make-up. In some instances, a boy can have some normal XY cells and some XXYY cells, this is called . A karyotype is the only way to know for certain that a boy or man has 48, XXYY.