The fact that we speak of X and Y “variations” means there are a variety of genetic profiles that differ from the typical. Examples include an extra X or Y chromosome for males, or an extra X chromosome for females. Since the discovery of such genetic variations in 1959, affected individuals and their families have struggled to find reliable sources of knowledge and support. Our purpose at AXYS is to be that resource for the spectrum of X and Y chromosome variations.

Whether you are a parent or adult looking for answers, a parent-to-be, or a medical professional seeking information on how best to serve your patients, you will find much to inform you here, as well as links to many other resources that can address nearly every conceivable need. And if you can’t find answers in the materials here, we maintain an active support network via phone, email and other means. Simply know that you are not alone, that help is here today, tomorrow, and for as long as you need it.

Welcome to AXYS.


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

CME (Continuing Medical Education) Courses


The Challenges of Klinefelter’s

"The Klinefelter Syndrome: Current Management and Research Challenges"—From the scientific journal, Andrology, this article summarizes the concluding “Round Table Discussion” of the 2nd International Workshop on the Klinefelter Syndrome in Munster, Germany, March, 2016. Topics [...]

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 [...]



Link to AXYS News and Newsletters

Link to the AXYS Library of Research and Treatment Articles


Four Common Questions

X&Y chromosome variations refers to conditions in which a person has an atypical number of sex chromosomes, also known as X&Y chromosomes. Other words used to describe X&Y chromosome variations are “sex chromosome anomaly,” “sex chromosome abnormality” and “sex chromosome aneuploidy.” Males usually have one X and one Y chromosome, and females usually have two X chromosomes. Occasionally, because of problems with the formation of a parent’s sperm or egg, or due to errors in cell division after the embryo is fertilized, a child can be born with extra or too few sex chromosomes.

Children are born with X&Y chromosome variations, but these conditions are typically not inherited. Instead, they are caused by a problem in the division of the X and Y chromosomes during the formation of a parent’s egg or sperm, or by errors in cell division after the embryo is fertilized. The exact cause is unknown.

The most common variations involve a trisomy, which means three sex chromosomes instead of the typical two. Girls who are born with an extra X chromosome are referred to as having Triple X or Trisomy X. Boys who are born with an extra X chromosome have 47,XXY, also known as Klinefelter syndrome. And boys who are born with an extra Y chromosome have 47,XYY, occasionally referred to as Jacob’s syndrome. In addition, there are a number of other X and/or Y conditions including 48 or 49 chromosomes. These include 48,XXXX, 48XXXY, 48XXYY and 48XYYY; and although increasingly rare, also 49XXXXX, 49XXXXY, 49XXXYY, 49XXYYY and 49XYYY. Some individuals may have two cell lines, which is called mosaicism, such as 46,XY/47,XXY.

Approximately 1 in 400-500 live births involves a baby with fewer or more than the typical two sex chromosomes. Researchers estimate that between 10% and 30% of all fertilized human eggs have either more or fewer than 46 chromosomes. These account for approximately one-third of all miscarriages. Variations in the number of chromosomes is the leading known cause of pregnancy loss. X and Y chromosome variations, however, are quite survivable. Although the rate of fetal demise of pregnancies involving X and Y chromosome variation is slightly higher than average, most of these pregnancies come to term. The exception is Turner syndrome, which affects females with only one X chromosome. The majority of these fetuses are miscarried.

Upcoming Events

Including support meetings, conferences, and webinars

Check back for upcoming webinars!

Special thanks to Clarus Therapeutics for sponsoring our current series of webinars.

Browse our previous webinars

September 26: SF Bay Area Support Group, Picnic/BBQ at Cuesta Park in Mountain View, CA | 12 – 3pm