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This karyotype includes one X and one Y chromosome —  normal. A man with XYY “syndrome” has an extra Y, but the only effect this may have is to be tall. (Figure credit: Darryl Leja, NHGRI)

by Jack El-Hai

This week’s New England Journal of Medicine has four articles about the new precision in reproductive genetic testing. (See Yet as genetic information increases, so too does the risk of genetic determinism – defining ourselves by our genes. But this is hardly a new idea. This week’s guest blog recalls a classic example of genetic judgment – the case of the man with an extra Y chromosome.

Jack El-Hai is the author of The Lobotomist: A Maverick Medical Genius and His Tragic Quest to Rid the World of Mental Illness and the forthcoming book The Nazi and the Psychiatrist. He often writes on the history of medicine and science.

A battered paperback entitled The XYY Man, by Kenneth Royce, leans in a corner of my bookshelf. It’s a spy novel that chronicles the adventures of “Spider” Scott, an ex-felon who wants to become law-abiding, but finds that he is genetically predisposed to criminality because he has an extra chromosome. Unlike most men whose XY sex karyotype imparts their maleness, Scott has been endowed with an XYY karyotype by his novelist creator.

This condition is not fanciful. XYY syndrome first appeared in the medical literature in 1962, eight years before Royce published his book. A team of researchers from Roswell Park Medical Institute in Buffalo, N.Y., described the first XYY person on record, a 44-year-old man who had undergone genetic testing because one of his children had Down syndrome. Though never before reported, this extra-chromosome condition produced during early cell division has turned out to be not tremendously rare, affecting about 1 in 1,000 boys. In most men who have it, the 47th chromosome causes no problems whatsoever, and more than 95 percent of XYY guys don’t realize they are specially endowed.

For decades, however, geneticists argued over the reputed social hazards of XYY syndrome. Did the extra chromosome make its bearers “supermales,” men who behaved as if they were amped up on too much testosterone? Some believed that XYY men, like “Spider” Scott, were inherently violent and prone to committing criminal acts. The dispute captured the public’s imagination, spawning several sequels to Royce’s novel along with numerous movies and TV shows (such as Law and Order) featuring dangerous and socially conflicted XYY characters.

During the late 1960s, geneticists, sociologists, and others began looking at prison populations to see if XYY men were disproportionately represented. (Note: Patricia Jacobs was lead author on the most famous paper about XYY, “Aggressive behavior, mental sub-normality and the XYY male,” and for this reason XYY is also called Jacobs syndrome.) Many people asserted that not only did XYY men commonly have violent criminal tendencies — the biochemist Mary Telfer characterized them as “perhaps too highly sexually motivated” — but that such males could be diagnosed by physical and mental traits, which included tall stature, long limbs, facial acne, mild mental retardation, and aggressive behavior.

In 1970 geneticist H. Bentley Glass advocated the relaxation of abortion laws to allow women to end pregnancies if the fetus was XYY. Speculation even ran that Richard Speck, the infamous murderer of eight student nurses in Chicago in 1966, owed his propensity to violence to an extra Y chromosome. That proved untrue. In one notorious case of the mid-1970s, a British court wrongfully convicted Stefan Kiszko of the murder of an 11-year-old girl largely because of his XYY karyotype, and it took more than 15 years for him to win release from prison. For further historical takes on the misunderstood extra chromosome see Y Envy.

In recent years, geneticists have learned more about the actual effects of the XYY condition. XYY boys may be delayed in maturation, are taller on average and more physically active, and sometimes display learning and behavioral problems. Their intelligence, testosterone levels, aggressiveness, sexual development, and fertility typically fall within the normal range. They grow into men who are unrecognizable to the general public.

In the mid-1970s, a Danish study showed that XYY men were not more likely to commit violent crimes, although they did have more convictions for other crimes. A long-running follow-up study published this year confirmed those findings and attributed the higher conviction rate for such crimes as sexual abuse, arson, and burglary to “unfavorable living conditions” — poverty, joblessness, and other disadvantages resulting from a lack of childhood support that many XYY men experience. (See Ricki’s take on a 2012 twin study on XYY.)

Slowly, as the suppositions of the 1960s give way to current research, the public is changing its thinking on XYY syndrome. Few people today believe that an extra Y chromosome condemns its owner to a life of violent crime. Genetic counselors explain the condition to families and teach ways to nurture XYY boys. Men like the fictional “Spider” Scott can exercise their free will without fear that a sex chromosome has turned them bad.

  1. Great post. My 13-year old son has yet to show any behaviors or symptoms as a result of his XYY chromosome makeup. He is very much like his peers and siblings in intelligence, athleticism, humor, height, attitude. I don’t engage in any forums at the risk of upsetting parents who are dealing with issues and searched the web out of mild curiosity to see if there was anything new out there on XYY. Thanks again for a well-written post.

  2. My son has XYY and has many diagnosis associated with this disorder. I am also on an XYY Facebook page and most of the boys experience the same symptoms- Autism, apraxia, hypotonia, dyslexia, macrocephaly, social and developemental disabilities, aggression, tall stature, acne,…there are 1-2 boys who are so mild that they do not show the traits as openly, but the majority have all of these issues at different/ varying degrees. There is a clinic in Denver, Colorado ‘the eXtraordinarY clinic. They deal with all X/Y disorders and we are hoping to go next year! There is a genome research project on the Y chromosome that I found that was very interesting from St. Louis. XYY is also thought to be rarer then prior research has shown. The Focus Foundation has some XYY information, showing it to be rarer then originally thought. There is not a lot of information because most people did not have genetic testing years ago, and it is only due to the recent testing and women having babies older that we are able to truly have a better sense of the numbers. On the blood work itself it states that they are more aggressive, have educational and social issues.
    My son is in 6th grade on a 2-3rd grade level, and tries so hard. I have 2 older children and he was different from the beginning. He did not talk until Speech Therapy by 41/2-5. He cannot tell a joke- he does not have the ability to relate information and put it together on his own so a lot of his language is adopted from what he sees/hears. He is charming, wonderful and makes life a better place- he is emotionally 5-7 and that has not changed in years. He is almost 12 and just started to dress himself fully [velcro shoes]. He has very poor muscle tone so his writing and tying skills are not age appropriate.
    I love him, and my goal is to help him live his dreams!

  3. Hello Jeannine,
    My name is Meisha , and my daughter is doing a biology project on Jacob’s syndrome. We are having difficulty finding what life is like for someone with this syndrome. I just came across your testimony and would like to know if she could share it in her report? It sounds like life is very challenging for your son but with the love of family anything is possible. We are hoping for the best for him.

  4. Hello,
    I just came across this site along with a few others. My son is now 23 yrs old with a successful lifestyle, but I will say he did have a difficult time in school. It takes a lot of patients, respect, responsibility, and of course love but with correct knowledge and support these kids turn out just amazing as any other kid.
    Good Luck & Best Wishes to ALL!

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