Most human beings are born with 46 chromosomes. Two of them are sex chromosomes, with females having two X chromosomes and males one X and one Y chromosome. About 1 in 18,000-40,000 males are born with an extra X and Y, resulting in a condition called 48,XXYY.

48,XXYY is one of multiple sex chromosome variations that affect males. Others include 47,XXY, 47,XYY, 48,XXXY, and 49,XXXXY.

Researchers have yet to discover the exact cause of 48,XXYY. There is no evidence that parents of one XXYY child are more likely to have other children with the condition or other sex chromosomal variations.

Diagnosing 48,XXYY requires a genetic test called a karyotype. It is performed with a simple blood draw and laboratory analysis.

Partly because of a general shortage of research on XXYY, it is often mistaken for other syndromes. It is also frequently—and mistakenly—referred to as a “variant” or “under the umbrella” of Klinefelter syndrome, which it is not. XXYY is its own condition, with a number of common characteristics. It is important to remember, however, that individuals can vary greatly in the number and severity of symptoms they exhibit. The most common symptoms are:

• Developmental delays
• Speech impairment or delay
• Tall height, often unrelated to family history
• Behavioral outbursts and mood swings
• Learning disabilities
• Intellectual impairment
• ADD or ADHD symptoms
• Autism, autism spectrum, PDD-NOS
• Scoliosis
• Clinodactyly (curved-in pinky fingers)
• Low muscle tone
• Flat feet/club feet
• Sterility
• Delayed sexual development
• Undescended testes
• Low or no testosterone
• Dental problems
• Leg ulcers
• Heart defects (i.e. VSD)

48,XXYY Brochure

For much more extensive information on 48,XXYY, visit the XXYY Project at xxyysyndrome.org.