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What are XXY Chromosomes?

Tricia Christensen
Updated Mar 03, 2024
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In most cases, when children are conceived, they inherit a chromosome from each parent that helps to determine gender: X chromosomes are female and Y are male. The female child has two X chromosomes (XX), and the male child receives an X and Y chromosome (XY). In some circumstances, occurring in between 1 and 500 to 1000 births, a male child receives an extra X chromosome, creating an XXY chromosomal structure.

XXY chromosomes, or more accurately, the XXY chromosomal structure or pattern, when recognized, can create varied symptoms. These are not always expressed and the condition is not always recognized. The presence of the extra X may be called Klinefelter Syndrome, or boys with one are referred to as XXY males instead of describing their differences as a syndrome. It is important for people to remember that boys with an extra X chromosome may have all or none of the features associated with XXY males.

Some indications of the XXY chromosomal structure may be noticed in early childhood. These can include physical developmental delays, like walking or talking later than average. Speech difficulties may continue, and children may require speech therapy. Learning disabilities in early school, especially challenges with reading, can also affect some of these children. Boys with this additional X chromosome may also be more physically awkward and some are more shy or passive.

If XXY males are not diagnosed in childhood, is may be discovered during puberty. The testicles are usually small and do not increase in size, as they do with most boys during adolescence. Many males with this extra chromosome are infertile, though not all of them are. Though these children may actually be taller than most, they may lack the normal signs of developing puberty, and can have rounder bodies, more breast tissue, and scant to no development of body hair.

These children often benefit from testosterone treatment during puberty to help produce adolescent development of adult male features. Lack of this treatment does not mean that sexual behavior in life is impaired, however, and many XXY males have normal sexual lives in later life, though some men may note slightly less interest in sex. The XXY chromosome pattern does not predispose men to be “feminine” or to "develop" homosexuality. Studies on this suggest homosexuality is just as common in men who have the more common XY chromosome arrangement.

Diagnosis, especially for those who exhibit key symptoms, can be helpful. Boys who are not aware that there are physical reasons for slight differences between themselves and others may feel they are “weird” or “different.” Education, treatment with testosterone as needed, and support from parents can be a great help.

Supplementation with testosterone can also help lower risk of certain diseases later in life. For instance, men who do not get this help may have a higher rate of developing osteoporosis. They are also more likely to be at risk for breast cancer since they have slightly more breast tissue than the average male.

TheHealthBoard is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Tricia Christensen
By Tricia Christensen , Writer
With a Literature degree from Sonoma State University and years of experience as a TheHealthBoard contributor, Tricia Christensen is based in Northern California and brings a wealth of knowledge and passion to her writing. Her wide-ranging interests include reading, writing, medicine, art, film, history, politics, ethics, and religion, all of which she incorporates into her informative articles. Tricia is currently working on her first novel.

Discussion Comments

By anon1004555 — On Mar 04, 2021

Please note that not all XXY are Klinefelter, but all Klinefelter will be XXY. Also, please note that a Y chromosome and a penis do not always make a boy/man's gender identity. When an XXY/Klinefelter grows up to have a voice, many of them come out as girls. With the "non-binary" option, many are picking this too, now.

The medical complex and government have invented sex to persuade these notions that a penis always has to belong to a boy. Sad to say, many XXY women were assigned boys in error. All intersex kids deserve self-determination over their own gender identity. The tragedy of assigning an intersex child's gender identity wrong has to end!

By anon1003524 — On Jul 12, 2020

This syndrome is not limited to reproduction. I discovered it after three DNA saliva tests from three different well known companies! Only then was I tested locally. I got a blood test to rule out xx syndrome!

What hasn't been discussed is what I know from from personal experience, such as how it affects the roots of my teeth, for example! My roots generally have large, thick bulbous ends. As for the DNA saliva test, the raw data yields surprising information, especially if tested with 23&me!

DNA testing in this way confirms whether the testis determining factor is pathogenic or not! Since I have all the raw data from the three tests, I am able to confirm the gene that yields trouble as well as those genes associated with other internal problems. The syndrome is not primarily about reproduction!

By anon972654 — On Oct 05, 2014

@anon964980: If these boys are this way and they are not experiencing any significant emotional stress, why would you want to complicate their already confusing lives by subjecting them to a hormone that will most likely do more harm than good?

By anon964980 — On Aug 08, 2014

I am curious about something. I am transgendered female to male who is transitioning. I am trying to research what might cause this problem, and came across this post. I have a feeling it can be linked to the chromosomes and that is how I ended up here. Something to note: I am from Florida but I live in Oregon now. I work in the school district and have noticed something about the males here in Oregon, especially the "white" males. Not all, but I would say maybe two of 25-30.

I'm very observant, and noticed quite a few of the boys at puberty age, have breast tissue, are not as masculine, and are seemingly introverted. They're not like some of the others who flirt with the girls etc. One I am thinking of just came out as bisexual and the other identifies as hetero. I have wondered, since I am on testosterone, if either of the two would benefit from testosterone supplementation but I have never said anything to them or anyone about this. These are just my thoughts. But something else I have thought- I never noticed this type of thing is Florida, where there is lots of sunshine and I have questioned if maybe the lack of Vitamin D has something to do with this? I wander how many of you are from areas where there is a lack of sunshine? Just a thought.

By anon963373 — On Jul 29, 2014

I'm 35 and have been recently diagnosed with klinefelter's. I exhibit all symptoms except infertility. When on trt I don't shoot blanks and actually produce a lot of semen. Without trt I have no libido. Finding out I have klinefelter's answered a lot of questions I had about my life. I am also starting to think I might be bisexual or gay.

By anon941330 — On Mar 22, 2014

Gender dysphoria is for transsexuals, not those who are transgendered. Huge difference! Anyway, I think I might have XXY, but I identify as female. I will talk to my doctor when I have a physical.

By anon941051 — On Mar 21, 2014

I find anon163617's posting very interesting. I too am developing breasts in my late forties. However, although I cannot lay claim to being fit as anon163617, it is definitely breast tissue, not fat. My childhood is very indicative of XXY, so I am pretty positive I am XXY, but unsure whether to get a doctor to test for it just to have a label placed on me. I wonder if there are more XXYs out there who can report later life breast development. It may be even worth a professional study.

By anon330805 — On Apr 18, 2013

What is it called when he has two testicles and a small testicle is attached to the right side of the testicle not the left. Two normal size testicles and then one small one attached to just the right.

By XXYGuy — On Apr 13, 2013

Well I say mmmmm. XXY is not rare. It is common -- so common it ought to be picked up more frequently, but because it's all about sex, it isn't. It's really strange the incidence rate of XXY at birth is between 1:500 to 1:1000 live male births, but the incidence rate of all the medical conditions associated with XXY are nowhere near that high. The most common medical problem is hypogonadism, and yet even XXY men who have it, and have had it for many years, are rarely diagnosed.

The most common reason for diagnosis after the onset of puberty is fertility testing, and they're usually found to be infertile. Before the onset of puberty it's learning difficulties, particularly delays in reading.

The rest of the time, XXY's are found by serendipity, or, by accident.

By anon329075 — On Apr 07, 2013

I was tested when I was younger and found I was XXY. I did have some of the things mentioned in this but without the breast growth. I wish. I've been living as a female since 2002 and I'm now 33. I've been on hormones and tblockers since then as well had my breasts done and will be getting an orchi later this year, hopefully. I'm glad I am XXY. It's not every day you can say your a rare kind.

By anon327444 — On Mar 27, 2013

Of course it's possible to transition, but in my view you'd need to have always thought of yourself as not really male, or really female, then later you discovered you're XXY, and then it would be more believable.

As it happens, it always seems to be the way that some people claim to be XXY guys, discover they're XXY, then develop gynaecomastia then determine they're not really male etc. And to me it just seems so convenient.

I've been XXY since conception, and always thought of myself as male. I did question the sex of XXY's initially, but soon put the notion to bed; we're male both genetically and physically.

I don't know why discovering you're XXY would cause you to develop gender problems, since you were always XXY. Therefore, you should always have had gender problems.

The only people who really need to be XXY when they transition are those who have always felt female and need an excuse that sounds acceptable to the lay people of the world. Chloe Prince is one such Transsexual person who pretends to be XXY. Most XXY's never question the obvious at all. They are male and they know it.

By anon323805 — On Mar 06, 2013

I was diagnosed with XXY chromosome when I was 16 years old. Since then, I've had the testosterone therapy. I get an injection of artificial testosterone each month, and forever.

Now I'm 20, not long ago I discovered that I'm bisexual, and since than I'm feeling more feminine inside than male outside. I like more and more males than women.

I can't stop thinking about how it would be to be a woman. Is it possible for an xxy male to transit to a female without problems in the future?

My question is, is it normal for me to feel like that?

By XXYGuy — On May 06, 2011

It's a pity anon163617 doesn't have a real name and his story can't be checked. The implication is that he was diagnosed as XXY for really weird reasons then in later life developed Klinefelter's syndrome, hence the 'man boobs' but one symptom of seminiferous tubule dysgenesis, which is the cause of infertility for XXY men.

Thus, the scenario is theoretically possible, but I've never read or seen any report of such a scenario. I think, without proof of the contrary, newly diagnosed XXY's should not assume they are or are not fertile.

By anon163617 — On Mar 28, 2011

I found out when i was having my first child (I'm male) that I had xxy. It was purely by accident that I found out as we had our blood tested as I had a history of down syndrome in my family. It did not bother me in the slightest until now at 53, I'm developing breasts, which I hate. I exercise regularly so it's not due to lack of exercise!

My kids say I have man boobs. It's starting to have a huge effect on me. I'm ashamed to take off my top on the beach and have not been swimming in ages. When I found out some 16 years ago, I was told nothing about it, was just told I was normal. Now after reading up on it a great deal it can explain a lot.

I have always had difficulty learning, I would have to do the thing to remember it, so I became very creative with my hands etc. If I had known this years ago my life may have taken a different route. I'm not unhappy, just hate my body shape.

By XXYGuy — On Feb 22, 2011

The research is needed to prove not all are infertile rather than that all are infertile. Effectively, the chances of a man with Klinefelter's syndrome being fertile are zero, but is it conceivable that those men who are XXY may not have the syndrome and are fertile. The reasons XXY's are discovered in from pre/postnatal genetic testing, difficulties in education (not common but possible), incomplete puberty and fertility testing in adulthood.

The medical profession argues that not all XXY's go on to develop the syndrome, as their explanation as to why the incidence rate at birth, between 1:500 to 1:1000 live male births, is not represented in fertility treatments for infertile couples.

By anon154718 — On Feb 21, 2011

Is there any research going on these kind of people, proving that all of them are infertile?

By XXYGuy — On Oct 27, 2010

I'd like to add more information about treatment options for XXY's but that would exceed the range of the original question. I see you do mention testosterone but there are additional surgeries as well that can be utilized. And testosterone does have side effects even in XY's that could be addressed? Is there a page regarding treatment options for males with Klinefelter's syndrome, or will here do?

By XXYGuy — On Oct 27, 2010

In early 1976 I was diagnosed with Klinefelter's syndrome which was confirmed by Karyotype later that year.

My visible symptoms at the time were very thin build, no musculature, no facial and sparse body hair, female pattern pubic hair, normal penile development, small firm testes (or testicles if you prefer?) No breast tissue was present, my span was greater than my height (all these things are relevant), I was not over 6 feet tall, merely 5'8" and I had broader hips than chest. My complexion was very pale, anemic almost.

The hidden symptoms revealed by blood tests were elevated LH (Luteinizing Hormone) and FSH (Follicle Stimulating Hormone) and low normal testosterone.

LH tells the testes to make testosterone and increases if there is insufficient testosterone production, FSH tells the testes to make sperms and also increases when insufficient sperm is created.

By mid 1976 I had testicular failure and had no testosterone production from my testes. I was 16.5 years old. It is estimated I developed Klinefelter's syndrome itself when I was 14 years old.

You may be interested to know that testicular volume by age 16 ought to be somewhere between 15 and 25mls volume, mine at age 16 were 1.0mls volume.

At that time I had my ejaculate tested and was found to have Ogliospermia, which means I had no sperm at all. I began testosterone therapy in October 1976 and have not ceased since.

My experience indicates the earlier the diagnosis the better, preferably before the onset of puberty. Recent information indicates there may be a greater chance of recovering viable sperms from XXY boys for storage later in life.

In my biased opinion, all boys who have learning difficulties should be Karyotyped just to see if they are XXY, obviously for their benefit alone.

By XXYGuy — On Oct 26, 2010

Re: transgender: XXY's are male anatomically. We have male internal structures and male external structures in most instances. We are definitely not hermaphrodites. With Sex Chromosome Abnormalities and how people think of themselves, the sky is the limit when it comes to who people want to be regarded as. But physically speaking we are male.

By XXYGuy — On Oct 26, 2010

My own personal experience here. I have school reports from my first year that show delays in reading, writing and speaking. I was frequently in trouble for not following instructions. I was thought to have petit mal epilepsy, and took medication for it treatment, that had no effect at all, apart from giving me a really bad mood, which was not helpful.

Later on, I was diagnosed with AD/HD Inattentive Type which has surprising similarities to petit mal epilepsy. I can understand why the error was made.

And my research indicates many XXY's suffer AD/HD throughout their entire lives, which is good as I still do. I do not recall being shy but I was passive and highly emotive. I definitely did not fit in with my peers and can only recall having one friend at any given time.

Difficulties have not subsided with age; they are constant.

By XXYGuy — On Oct 26, 2010

The doctors who discovered the XXY Karyotype in men with Klinefelter's syndrome were Jacobs and Strong from Canada in 1956.

Dr. Klinefelter proposed there may be a genetic cause for the syndrome he first described in 1942. At that time there was no such thing as Karyotype testing, nor indeed did Jacobs and Strong have Karyotype testing; they used Barr Bodies, which are the shadows left by the inactive X in females. Therefore man will have no Barr Bodies unless he's XXY. Easy eh!

By XXYGuy — On Oct 26, 2010

I have found four reports of XXY males transitioning to female. I know of thousands of XXY males. On that basis I'd say XXY's were not Transgender simply because they're XXY. And those who do transition and cite XXY as their sole reason are misguided.

By XXYGuy — On Oct 26, 2010

XX and XY and XXY are described as karyotypes, not "structures" I have an XXY Karyotype for example.

By XXYGuy — On Oct 26, 2010

As an XXY man myself I'd say there was no delay in entering puberty but puberty did not proceed as it should have due to lower testosterone level. Sexual interest is impeded greatly by that lower testosterone level as is sexual function.

Overall, this article is much better than others I've seen here on this topic.

In 2008 a report was published showing XXY pubertal boys and men do indeed have sperms in their ejaculate, and may not be as infertile as first described by Dr. Harry Klinefelter. It may be that as XXY's age they become less and less fertile?

By anon121945 — On Oct 26, 2010

The Drs who discovered the XXY karyotype was not Dr Harry Klinefelter, he is the Dr who had his name first on the paper that described Klinefelter's syndrome in 1942, Klinefelter et al. The persons who are responsible for discovering the XXY karyotype are Jacobs and Strong from Canada in 1956.

I'm Graeme and I'm XXY and all male.

By anon115188 — On Oct 01, 2010

We are not transgendered. We are not transitioning to an other sex. Hope this helps, ha. --David K.

By anon75497 — On Apr 06, 2010

Are these people transgendered? If the chromosomal abnormalities result in gender dysphoria they are considered Transgender. If the chromosomal abnormalities result in parts of both sexual anatomies, they are considered Hermaphrodites.

Hope this helps!

By anon51081 — On Nov 03, 2009

are these people transgenders?

By anon25034 — On Jan 22, 2009

XXY means there are 3 chromosomes: 2 x's and a y. So, you can't say "an XXY chromosome" or "XXY chromosomes."

Tricia Christensen

Tricia Christensen


With a Literature degree from Sonoma State University and years of experience as a TheHealthBoard contributor, Tricia...
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