XYY -- Stereotype of the Karyotype
Edward R. Friedlander, M.D.

Ed in scrubsI'm Ed. I'm a pathologist in Kansas City, and run the largest free personalized medical information service on the internet.

I am tall, lean, and physically powerful. At age 47, I still take medicine for acne. I have a temper that I work hard to control. And I've learned to avoid situations that set me off. I have never physically hurt anyone in anger.

I've got my faults. I'm a macho, generally well-liked man who enjoys being single and tries to live clean. There's been some romance, and no real problems here. A few women have even said I look okay and/or am a nice guy.

My muscles are stronger than they are coordinated, so I've focused on strength-endurance sports like gymming and swimming. But I'm a fair keyboard player.

I've got a pectus chest deformity and a wiring problem with my left eye. Cognitively, I'm a little "different" and always have been. But it doesn't bug me.

Uhh... do I sound like something you've read about recently?

If you are visiting, you perhaps:

Most males have the 46-XY karyotype, but about 1 guy in 1000 has two Y chromosomes, and is an XYY ("diplo-Y", "diplo Y", "YY", "polysomy Y", "Jacob's syndrome"). If XYY men are at any greater "risk" of fathering XYY or XXY sons, the increase is small (Zygote 7: 131, 1999; <=1% Reproduction 121: 655, 2001).

When first discovered, popular science writers speculated that the extra "Y" would make owners act more masculine -- i.e., more aggressive, irresponsible, and criminal. Uh-huh. Richard Speck, the killer of eight student nurses, pretended (falsely) to be an XYY to obtain leniency, thus popularizing the "XYY's are criminals" story. The famous Nielsen letter in Lancet Sept 7, 1968 claiming that the prevalence of XYY men in prison was "25-60 times as high as the prevalence in the general population" remains a shocking example of how to mislead the public using small-sample statistics -- there were only two XYY's identified in the study. Aliens 3 was set in an offworld "penal colony for XYY's", and folklore continues to this day.

There's no question that XYY's average substantially taller, tend to be wiry-built, and tend to have severe acne. Minor birth defects -- like pectus, crooked eye, and minor outturning of the elbows, are supposed to be common in XYY's.

It will probably not surprise any adult visitor to this site that the average blood testosterone (the rocket-fuel that drives male sexual characteristics and behaviors) averages much higher in some men than in others. XYY's average higher than XY men. Men in prison average higher than men not in prison. When you control for the high testosterone levels, the most recent published study (Arch. Gen. Psych. 41: 93, 1984, from Copenhagen) showed there is no over-representation of XYY men in prison. ("Information from social records, a structured psychological interview, and projective tests did not support the notion that men with sex chrmosome anomalies are particularly violent or aggressive.")

XYY's average only slightly lower intelligence than XY's, and the range is the same for both groups. If XYY's really exhibit severe behavior problems, it has resisted demonstration by the best scientific minds in the field of genetics. Here's why -- it's something called "ascertainment bias". Kids who are screened for chromosomal problems tend to be learning and/or behavior problems. If they come up with XYY, it's easy to blame the karyotype. What's more, somebody doing bad science can get up a series: "Look at all the XYY's I've discovered, and most of them have mental problems!" (See the fallacy?) But to date, nobody's shown that XYY's are more common among kids who are screened for these problems than in the general population. And if XYY was itself a major problem, you'd think this would have been accomplished long ago.

Now, XXYY boys traditionally been considered at increased risk for emotional and cognitive problems. (For an update on XXYY from a parents' group, see http://xxyysyndrome.org/". The condition is rare enough that we're still in the "single case report" stage; the most recent work seems to confirm the prevailing wisdom, but once again, we don't see the picture of violent criminals (Arch. Gen. Psych. 56: 194, 1999), and one always wonders about ascertainment bais. The extra "Y" in an XYY is obviously not silent (as is the extra "X" in a XXX woman). It seems likely that the second "Y" adds a bit more aggressiveness to a man's overall personality. And I don't know that this is necessarily a bad thing. Despite decades of male-bashing from the Left, I think most people still like a man (or woman) who is responsibly aggressive.

When I'm certain I won't lose my own health insurance, I'll find out for certain whether I am an XYY. In the meantime:

I hope you came here wanting straight answers. If your boy has XYY, give structure, fairness, love, and time with Dad or a good substitute to teach him how a happy, good man should act. You'd do this for any boy. In the politicized climate of genetic counseling, you'll probably get a welter of confusing information "so that you can make your own decision" about abortion. I'm NOT your doctor, so I can talk straight.

After reviewing the evidence, I find no reason to think that XYY makes men crazy, retarded, or criminals.

If you are considering ending the life of your unborn child "just because he is an XYY", don't do it.

Dr. Greene's XYY notes.

A site called Intersex Resources for Christians is now down.

Ed's notes on genetics with references.

Current articles from the refereed medical literature:

One scientific study that is conspicuous by its absence is a look at overall achievement by XYY's who choose military careers. It would be fairly easy to do in the countries where there was a great deal of prenatal screening. If anyone knows of an unpublished study, please let me know.

Science in Dispute carries an out-of-date article on xYY. Although there are some recent references, the writer refers primarily to articles more than two decades old. "Much more recently" refers to an article from 1988. She also refers uncritically to the Gotz study as if the fallacy (one rotten apple) wasn't obvious.

Ed's home page


New visitors to www.pathguy.com
reset Jan. 30, 2005:

Afterwards: I have received dozens of E-mails about this page from parents of XYY boys. Most of them shared that their sons showed no particular behavior problems. Several mentioned their sons having short fuses and being hard to handle when they are angry, but that's been all. Others have expressly said there's been no particular temper problems. To date, not one of them regrets bringing their boy into the world.

Only one correspondent so far has described a sociopath (i.e., a lifelong pattern of heartless indifference to the rights of others, even those who treat him with kindness). Sociopathy is all-too-common, and the vast majority of sociopaths have a normal karyotype. Despite the correspondent's feelings about the cause of her brother's behavior, it is hard for me to see anything but a coincidence.

Here are E-mail addresses of some folks with XYY sons / XYY. To date, only one family has asked that their e-mail be removed, some years after it was posted.

jomama26@panola.com -- Tommy and Vicky Watson are happy with young Joe
krspykreme@aol.com -- very happy with young David
domain_master52@hotmail.com -- Jay Carswell is an XYY mosaic. He describes the bony fusion in the elbows. "I am very happy with who I am."

glaceir14@aol.com -- Matthew is a young adult who recently learned of his karyotype. He tells me that people are surprised to learn this, since they say he's "one of the nicest guys they know."

studyquestions@aol.com -- Lorenzo writes:

We have a son, 11 years old. We were counseled about an abortion before the child was born. Today he had a checkup. He is perfectly fine at this stage. At the counseling session we heard same stuff about criminal behavior and aggression. I thought, that this unborn child was going to be a rapist.

(Follow-up: September 2011) He is now entering a fancy university in Northern California based on his grades and SAT scores. http://historyofxyyboy.blogspot.com/


spakizer@neogen.com Stephanie Pakizer is married to "a great guy wity XYY".

banjoid7@yahoo.com Mark LeMond, in Oklahoma, says he is the parent of an XYY son "who is truly wonderful at six months old." He invites other parents of XYY's to mail him.

mlwgds@telus.net -- Leanne and Mike Stewart are very happy with Greg, who's now a teenager. "What a cool kid!" "We have had people contact us to discuss their XYY sons with us. It has been a pleasure to let them know our son Greg is doing very well. He is now in grade 12."

Our XYY Son -- link is now down.

Rachel Cooper (pseud.) has written a book about an XYY son called "Hidden Tears and Happy Smiles", available from Lucky Duck Publishing.


A family whose e-mail no longer works writes:


Tiani from Alaska asked me to protest CBS's decision to portray XYY as "criminal genes" in a show on May 13, 2007. (I have never owned a television, but as a pathologist, what I hear about the show tells me that much of it is just Hollywood.) She characterizes her 8-year-old XYY son Joey as "a wonderful, loving boy, through and through... smart as a whip and very creative -- but impulsive, naturally.... At just-turned-8 he is over 1 1/2 feet tall already. No couch potato here, no games that would encourage sedentary participation -- he's outdoors nearly year round." She advises parents who have trouble with school bureaucracies to contact the Disability Law Center.

Jonathan. "I think he's pretty much a normal kid."

Mark from New York (e-mail available from me):

I have read your detailed research rebuttals and am impressed with your site. I am 31 years old, owner of my own business, 6'2", have occassional acne, and slight hyper extension of my elbows. I have a 130 IQ (tested), no social problems, or criminal history. I am happily married and plan to have children. I just found out I was 47XYY, just testing out of curiousity as to why I am so much taller than my parents and sister. I just want people to know that I knew all of this before I knew I was XYY. Don't treat your kids any different, and Im certain they will embrace life as I did. they are no different. If anything, they are better.


One of my cyberfriends, who has a son on the way with XYY, wrote me:

I am a physicist in Israel and expecting an XYY son to be born on March 2008. Your page on the topic has proven very useful to me in gathering info on the topic, and allaying the concerns of my family. I thought I would add one correction to your bibliographic summary on the topic: in your description of the 2003 article in Gen. Couns. you did not mention the fact that out of the 38 individuals studied only 12 were prenataly diagnosed, the rest were diagnosed after being referred for genetic testing due to ADD, violence, autism or other problems. There is a slightly increased percentage of these problems also among the 12 diagnosed prenataly, but the sample size in this case is far too small to make a clear statement on the matter. Furthermore the autism referred to (which was the most worrying issue for me) was observed only in the late diagnosed group, making this claim completely unfounded in my opinion. I will be happy if you add this info to your page.

Share yours? Mail me at erf@kcumb.edu. Thanks!

Addendum: Several subscientific pages are now down. One particularly bad page (formerly at www.genetic.org> is thankfully now down. There's also a YouTube video that anyone who's read this page will recognize as bogus.

I also cannot recommend a pamphlet, supposedly from a British academic department, that states (for example), "The majority of XYY men (around 75%) are in employment (sic.) Typical jobs include self-employment in business, catering workers (chefs and waiters), clerks, shop assistants and community service workers." I am not aware that this is anything more than the author's personal impression. Since she deals with people who are already identified as abnormal and are coming to see her to get checked, my best guess is that this has tainted her "series". Unlike most publications from academic departments, no other member of the department was willing to place their name on her pamphlet. Draw your own conclusion.