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What is Jacobs Syndrome?

Laura M. Sands
Updated Mar 03, 2024
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Jacobs syndrome is a genetic disorder that results in male children possessing an extra Y chromosome. Not to be confused with the XXY chromosome that causes sterility in males, this condition does not usually result in any major physical abnormalities. Also known simply as 47,XYY, males with Jacobs syndrome do, however, grow to be taller than most males without this condition.

Normal people have a total of 46 chromosomes per cell. Out of these 46 chromosomes, two are the X and Y chromosomes, which determine whether a person will be born female or male. Those who receive two X chromosomes are born female, while those born with an X and a Y chromosome are born male. Individuals with Jacobs syndrome, however, have a 47th chromosome, which is an extra copy of the Y chromosome.

There is no known cause for Jacobs syndrome. Research indicates that this anomaly happens randomly and does not appear to be an inherited trait. While there also do not appear to be any major physical abnormalities in males with this syndrome, there do appear to be other differences between boys with this condition and those who are not born with an additional Y chromosome. Primarily, these differences include learning disabilities, delayed motor skill development, speech delays, behavioral problems and hand tremors.

At birth, parents and caretakers do not realize any abnormal symptoms associated with Jacobs syndrome. Boys with this condition do show signs of slower than normal rates of emotional maturity, as well as being slightly more physically active than others. By preschool age, some minor learning delays as well as speech delays may be noted, but these do not usually present a major interference in a boy’s learning or overall maturation.

Physically, boys with this condition appear to mature at the same rate as other boys in their age group. The only remarkable difference is that boys with an extra Y chromosome tend to grow taller than average, but not abnormally so. Males with this syndrome progress to puberty at the same rate as other boys, are fertile and do not present any hormonal differences from others boys and young men their age.

Mentally and emotionally, boys with Jacobs syndrome do show a very slight risk of developing mental and social issues, but only if they are not reared in loving and supportive environments. Research shows that males with an extra Y chromosome who are reared in poor environments where stimulation and love are lacking show a slightly increased risk of developing maladaptive behaviors than other siblings in the same home. At one point in history, this condition was widely associated with criminal behavior, but contemporary research has proven that this simply is not true.

The Health Board 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.
Laura M. Sands
By Laura M. Sands
Laura Sands, the founder of a publishing company, brings her passion for writing and her expertise in digital publishing to her work. With a background in social sciences and extensive online work experience, she crafts compelling copy and content across various platforms. Her ability to understand and connect with target audiences makes her a skilled contributor to any content creation team.
Discussion Comments
By burcinc — On Feb 12, 2014

My sister's son has Jacob's syndrome, he is nine years old. He was diagnosed when he started school because it was taking him longer than his peers to learn and he had some behavioral issues. He now goes to a special school where he is given more attention and he has caught up with kids his age. He's probably going to return to public school next year.

Kids with Jacob's syndrome are just as bright as anyone else. They just need a little extra attention and care. I completely agree with the article, that if they are given the right support, they will not have any problems in life.

By ZipLine — On Feb 12, 2014

@fBoyle-- There was a study done in the past on the relationship between men with XYY chromosome and criminal behavior. The result showed that these men were more likely to engage in criminal behavior. But there was a major problem with this study, they did not control for socio-economic conditions. The men in the study lived under poor socio-economic conditions. So their increased likelihood to engage in crime might be due to poverty, not their genetic makeup. A skewed study like this cannot be taken seriously, it is just not accurate.

So those with Jacob's syndrome are not more likely than their counterparts to engage in crime. Sources that say the opposite are outright wrong. They need to update their information.

By fBoyle — On Feb 11, 2014

I think that Jacob's syndrome is still linked with criminal behavior. I have not seen any studies on this connection, but many sources still mention this as part of Jacob's syndrome symptoms. It's unfortunate if there really is no connection and people are being misinformed.

The same thing is actually also said about Turner's and Klinefelter's syndromes.

Laura M. Sands
Laura M. Sands
Laura Sands, the founder of a publishing company, brings her passion for writing and her expertise in digital publishing...
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