Looking for answers? We can help.

A doctor or other health care provider’s learning is never done. It is therefore no surprise, given the vast range of serious medical conditions affecting human beings, that many medical professionals are perhaps only vaguely familiar with X and Y chromosome variations. So we thank you for visiting this site, and we hope it will be helpful to you. We trust you will find here a useful initial storehouse of information and personal narratives that will assist your further investigation into these conditions.

The sampling of frequently asked questions below are complemented by an entire page of them that address many other aspects of sex chromosome aneuploidies. Just click here.

In addition, AXYS has developed a Clinic and Research Consortium with sites around the U.S., staffed by experts who are available for consultation on any matters pertaining to X and Y chromosome variations. Click here for a list of clinics and contact information.

Frequently Asked Questions

Variant karyotypes of 47,XYY, are probably not survivable in most cases.  There have been a few case reports of karyotypes such as 48,XYYY, or 49,XXYYY.  These individuals have had quite severe disability.
A mosaic cell line means that a man has one cell line with 46 chromosomes, for instance, including one X and one Y chromosome, as well as a second cell line with one X and two Y chromosomes.  This genetic signature would be written as 46,XY/47,XYY.  The term “mosaic” is used because the cells with different numbers of chromosomes “nest” together in a mosaic pattern, much like tiles on a floor or wall.
Approximately 80 percent of those with 47,XXY have the 47,XXY genetic signature.  In the other 20 percent, there may be more X and Y chromosomes, with genetic signatures of 48,XXXY, 48,XXYY, and 49,XXXXY. Or, individuals may have a mix of cells within the body, some XY and others XXY, which is called mosaicism. Some individuals have a genetic signature of 46,XX, but have a tiny piece of the Y chromosome appended to one of the X chromosomes, giving them male genitalia and secondary sex characteristics, such as facial hair and male muscle development.47,XYY is incorrectly associated as a variant of 47,XXY, but it is actually a distinctly different sex chromosome aneuploidy. The most obvious difference is that 47, XYY males have none of the medical and infertility issues that individuals with 47,XXY may have, although there can be behavioral difficulties and learning disabilities associated with XYY.
In girls and women with extra X chromosomes, about 10 percent will have 48 or 49 chromosomes. The variation with 48 chromosomes is called Tetrasomy X while the variation with 49 is called Pentasomy X. With each additional X chromosome, there is usually a decrease in IQ of about 15 points, as well as additional disability in various areas. Girls and women with Tetrasomy and Pentasomy X often have cardiac anomalies as well as genitourinary malformations or other birth defects. Unlike females with Trisomy X, many are infertile or fail to go through puberty normally and require estrogen treatment. Intellectual disability is not unusual in this population. It is also possible for a female to have only one X chromosome. This is known as Turner syndrome. It occurs at a rate of approximately 1 in 2000 to 2500 live births; only approximately 1% of fetuses with Turner syndrome survive to term. Most miscarry. Turner syndrome has a very different presentation from the trisomy sex chromosome aneuploid conditions. Girls and women with Turner syndrome usually have short stature and are infertile. They can have cardiac and other health problems.


Males with XXYY Syndrome are often diagnosed with other medical conditions or syndromes (or they may appear to have these conditions) before the XXYY diagnosis is made. These include:

  • Asperger Syndrome & Autism
  • ADD
  • Pervasive Developmental Disorder (PDD/NOS)
  • Sensory Integration Dysfunction
  • Hypotonia
  • Developmental Disability & Delay
  • Fragile X Syndrome
  • Epilepsy
  • Prader-Willi Syndrome
  • Speech Delays
  • Heart Problems
  • Hand tremors
  • Gynecomastia

Because many medical professionals have never had a patient with XXYY, it can be difficult to identify them.  We have published this document (link below) to help you to identify potential XXYY patients.  We created this booklet especially for outreach to Autism and ADHD groups and parents of children with those conditions because of the high rate of these two conditions in XXYY.

How to Identify XXYY

We also ask that you refer families to us.

Additionally, please note that older medical information on XXYY Syndrome is very limited and often out-dated. Males with XXYY are NOT necessarily violent. Such studies were conducted in prisons. Subjects did not have the benefit of correct diagnosis and treatment. Males with XXYY most likely DO need hormone replacement therapy. HRT does not make them aggressive. In fact, the opposite is true.

Mental Health

Mental Health professionals are in a unique position to assist in identifying males with XXYY Syndrome. If you see a patient with the following characteristics, coupled with other medical and learning problems or characteristics listed on this site, please refer him to his primary care physician and ask for genetic testing:

  • Moodiness
  • Bi-Polar disorder
  • Frustration
  • Outbursts
  • Difficulties in social situations
  • Extraordinary imagination
  • Difficulty telling the truth

Males with XXYY Syndrome often have unusual reactions to medications. Parents have found that ADD medications used at high doses can positively change behavior along with helping with attentional problems. Other medications for mood stabilization, etc., can seem to work for a while but then make matters worse. We encourage parents to keep written logs of changes in behavior of any kind after beginning medication treatments.


Males with XXYY Syndrome have unique and very prominent dental problems. Look for:

  • Taurodontism
  • Missing adult teeth
  • Poor enamel
  • Poor dental hygiene


Teachers are an extremely important piece of the XXYY puzzle. Males with XXYY are visual learners. They often hide in small places (under the desk, for example) because of sensory overload. Because of hand tremors, they may have significant difficulties with writing. Behavior outbursts may also happen.
The XXYY Project will be working on developing Individual Education Plans in the future. If you are a special education teacher and would like to contribute to the project, please contact us.

Speech, Physical and Occupational Therapists

Therapists, especially speech therapists, are often the first to see a male with XXYY Syndrome since speech delay is one of the first symptoms to become apparant. Some parents have found the use of sign language when a child is young seems to reduce frustration considerably. Because of low muscle tone, males with XXYY Syndrome need strengthening exercises for all muscles. A plan that includes all three therapies is the best possible assistance that can be given to a male with XXYY Syndrome at an early age. Occupational therapy is very valuable and if it can be done in conjunction with some training for the classroom teacher, it is most beneficial.

Brenda’s Story

“One thing I am rapidly learning is how much contradictory information there is about X and Y chromosome variations in the medical community. Interestingly, my baby has no developmental delays yet but he has more physical characteristics than most of the babies I have seen on the AXYS website. Clenched fists, deformed ear lobes… slanted eyes…one drooped eyelid…But he is a little ball of personality!”



Professionals who specialize in XXY, XYY, Trisomy X, and XXYY

Research and clinical trials for those with XXY, XYY, Trisomy X, and XXYY.

Clinics for individuals with XXY, XYY, Trisomy X, and XXYY

Support groups for individuals with XXY, XYY, Trisomy X, and XXYY

Latest News and Research

For a library of past news items, click here.

Exploring the Strengths of Students with X&Y Variations

"Children with sex chromosome aneuploidies (SCAs) are often characterized in the literature by limitations and pathologies related to the genetic diagnosis. This study aimed to broaden the SCA phenotype by describing parent reported character and [...]

A Klinefelter Update for Pediatricians

"Advances in the Interdisciplinary Care of Children with Klinefelter Syndrome"—This nearly 30-page story in the journal Advances in Pediatrics is directed at pediatricians and family physicians who treat children, and who may thus come across [...]

  • DNA strand

The Triple X Syndrome Phenotype

"Expanding the Phenotype of Triple X Syndrome: A Comparison of Prenatal Versus Postnatal Diagnosis" —This cross-sectional study was published in the American Journal of Medical Genetics. It describes the diagnosis, physical aspects, medical problems, and neurodevelopmental [...]

Exploring Klinefelter Syndrome

"The Impact of Living with Klinefelter Syndrome: A Qualitative Exploration of Adolescents and Adults" — This research article examines the medical, psychological, and social challenges that arise in individuals with 47,XXY as well as providing practical [...]