What is XYY Syndrome (47) ? Causes, Symptoms and Diagnosis

XYY Syndrome

Historically, there has been much confusion with chromosomal disorders and distinguishing how they occur. These disorders develop when an imbalance occurs and male and females disorders are very different. 

Whilst most people, male and female, have 46 chromosomes in each cell, 23 X and 23 Y, there are rare conditions where people have more or less, causing a genetic chromosome imbalance.

XYY syndrome is a rare chromosomal disorder where a male has an extra Y chromosome. It is a disorder that only affects males and in some cases, it remains an undiscovered disorder until adulthood if the symptoms are not noticeable. According to the National Institutes of Health, 1 out of 1000 males can be affected by XYY syndrome from childbirth. 

Read our guide for a deeper understanding and more information of this men’s syndrome : XYY

What is XYY Syndrome? 

A brief description helps sum up XYY syndrome, but it does not exactly go into detail of how it happens, when it was discovered and other details you will want to know. 

This syndrome is characterised by having an extra Y chromosome, which causes an imbalance. An imbalance in cell count can cause many other conditions, but for males who attain an extra copy of the Y chromosome are diagnosed with XYY syndrome. 

It is a disorder that can cause either small and unnoticeable symptoms. Mostly, those who are born with the extra Y chromosome and develop this condition live normal lives. However, in extreme cases patients show physical abnormalities and/or more severe cases of common mental conditions that are linked with XYY syndrome. 

Most babies born with XYY syndrome are not aware of the existing condition until later on in life. Some symptoms can be so mild they are unnoticeable. On average, only 10 percent of babies that have the syndrome are diagnosed before being born due to regular medical testing. 

To prevent any future confusion, it is important to know that XYY syndrome is also referred to as Jacob’s syndrome or 47, XYY syndrome, YY syndrome or XYY karyotype. The names all represent the same issue, that there is an extra Y chromosome than usual. 

Here is a quick video explaining XYY syndrome and the myth around “supermale” :

You may be wondering how a male can know if he has XYY syndrome. Here is an overview of each symptom and how it becomes a recognisable syndrome:

Symptoms of XYY Syndrome

The effect of the syndrome typically lets those with it live normal lives. Unlike other genetic syndromes or typical medical conditions, the symptoms vary depending on age. For example symptoms of a baby include delayed motor skills and speech difficulties. A toddler could experience autism, emotional and behavioural issues and tallness. When a male is fully grown and has gone through puberty, an adult symptom includes infertility. 

Physical symptoms 

Hypotonia – weak muscle tone

Neurologists findings show that around 63% of those with XYY syndrome develop hypotonia. Hypotonia is also referred to as floppy baby syndrome. It is where the baby has weak muscles and has more tension than normal babies to stretch or resist. Healthy muscles are usually never relaxed, but those with hypotonia have relaxed muscles most of the time, causing more strain with muscle movement. This issue may continue into adulthood, but it can be managed and treated. 

Hand shaking or unexpected muscle movements

Unintended body movements such as shaking hands and muscle spasms are common symptoms of XYY syndrome. A study shows that 43% of boys, 39 out of 90, show symptoms of unintentional tremors and motor tics due to XYY syndrome. These tremors commonly occur when the body is resting or mild activity. It does not usually affect day to day life but some cases are physically noticeable and straining on the body. 

Being taller than average

Most males, not all, who have XYY syndrome are taller than their peers. It is common to reach around 1.88 metres tall or more. The tallness does not usually occur until the boy reaches 6 years old or more and when it happens, the height is not abnormal but noticeable when comparing to heights of boys without the syndrome.  

Physical abnormalities

These physical symptoms are separate from being taller as they remain a mystery seeing as they have not yet been fully researched yet. But it is important to know that there have been other physical abnormalities reported in relation to XYY syndrome. These abnormalities have been reported as large teeth, flat feet, a large head, increased belly fat, widely spaced eyes and unusual curvature of the spine. 

Speech difficulties

One of the most concerning areas is speech as most XYY syndrome sufferers deal with speech difficulties throughout their life. Some early studies on speech issues show that boys with the extra Y chromosome have double the chance of speech delay than those without. 

Typically those who are at school suffer with the worst symptoms and case of speech delay due to regular tests. They have trouble with expressing themselves visually and verbally as well as having decreased memory skills. However, intelligence level (IQ) is not usually affected neither is day to day learning. It is easy to work on speech difficulties through therapy. 


Most research for the infertility rate in those with XYY syndrome has proven difficult but some studies show results that suggest it is more common in men who have the syndrome. A small study on three XYY patients concluded that all of them had a 2 year or longer stage of infertility in their life. These patients also showed signs of smaller than normal testes. All patients had other physical symptoms such as being taller than average and a high BMI. 

Research does show that the extra Y chromosome is lost before the meiosis process, where cells split during sexual reproduction, which may decrease the effectiveness of fertility. However, this symptom is considered to be rare. Even if the patient suffers with infertility, it is not always a long-term issue that can cause indefinite infertility. 

There have been no reports of a male with XYY syndrome being unable to have a baby. The symptoms usually last for a few years before the male becomes fertile again.

Mental symptoms

Delayed motor skills 

Although intelligence is usually unaffected, motor skills may be delayed during younger years. For babies, their walking and crawling process may be delayed when they are born with XYY syndrome. When the babies grow into toddlers and young boys other motor skills including writing, may be delayed. 

Also, those affected could have a weaker IQ than their siblings of around 10-15 points, but it is not always the case. It is typically motor skills that are delayed and affected, not the intelligence. 

Emotional or behavioural issues

Those affected with XYY syndrome could be at risk of having emotional and behavioural issues with unaffected family and friends. These issues include attention deficit/hyperactivity disorder (ADHD), anxiety, depression and in some cases, a development of autism. 

Whilst these symptoms may seem comparable to other medical conditions, they are often a symptom of XYY syndrome that people dismiss. The physical symptoms are more recognisable, but mental issues may be a sign of the disorder.

Moreover, here are a few causes of XYY syndrome and risk factors that come with the disorder:

XYY Syndrome: Causes, consequences and risks factors

The exact cause of XYY syndrome is still a mystery and has been left undiscovered. It is suggested that XYY syndrome is not 100% a genetic disorder, nor it is inherited. Most cases are due to a random error occuring during the sexual reproduction process. 

Physical causes

In most cases, XYY syndrome is down to a cell error where they divide in the sperm prior to conception. In rarer cases, the splitting of the cells occurs after conception and happens when the egg and sperm meet.  

There are little to no risk factors. The only physical issues that XYY patients have to deal with are symptoms such as physical abnormalities, speech difficulties and rare infertility. 

Mental causes 

As the syndrome is largely down to random error and is down to the physical aspects of the male body, there are no studied or conclusive results of mental causes. 

However, the disorder can sometimes cause mental issues. It is common for mental symptoms to develop for those with XYY syndrome such as ADHD, attention issues, autism, bad temper and behaviour. These symptoms can become risk factors for some patients, especially those who choose not to treat it.

If left untreated, mental disorders can worsen over time and become a whole other issue for the patient. Some mental conditions can be relatively mild, but they are known to progress over time if left untreated. 

The most recognised method of treatment for these mental conditions are medications and/or therapy. For example, ADHD has been commonly treated with a medication called methylphenidate. In a large study, three quarters of the XYY patients that had symptoms of ADHD were treated with this medication successfully. 

Furthermore, studies have found that behavioural and mental issues are more of a concern in this chromosome syndrome than any other. Klinefelter syndrome is a condition closely comparable to XYY,  but has very different symptoms. In this case, the behavioural symptoms and risk factors are worse for XYY patients. 

Diagnosing XYY syndrome has been known to be many years after having the condition due to its sometimes hard to notice symptoms. Let’s talk more about the diagnosis process and what’s involved:

Diagnosis of XYY Syndrome

When children, or even adults, show common symptoms of XYY syndrome, a test is usually recommended. Most commonly the diagnosis test involves a specialised blood test, commonly referred to as karyotyping or microarrays. Alternatively, some doctors suggest getting a chromosome test which can detect an extra copy of the Y chromosome and diagnose whether or not the patient has XYY syndrome. 

For those who test babies during the prenatal stage, there are two options. Amniocentesis is where the mother will undergo a test where a small amount of fluid that surrounds the baby is extracted and analysed. The second option is chorionic villus sampling (CVS), where tissue is removed from the placenta and assessed.

All tests on unborn babies, children and adults are successfully effective. All that is needed to be shown in the results in the extra Y chromosome which is easy to test for. 

It may be helpful to know that there are other male genetic disorders that could be mistaken for XYY syndrome. Relatable disorders may help for an easier diagnosis. The commonly mistaken male genetic case for XYY syndrome is Klinefelter syndrome where a male has an extra X chromosome.

Klinefelter syndrome sometimes varies and results in males having extra X and/or Y chromosomes, which is rare but has happened. These extra chromosomes affect physical, mental, behavioral, cognitive and emotional functioning. 

Knowing that there are different symptoms may be useful for diagnosis. Symptoms of Klinefelter include delayed puberty, small testes and breast development in adolescence. These are very different in comparison to XYY syndrome and affect the physical appearance more. 

For diagnosis, you must get a professional test like those discussed above, to ensure clinically tested guaranteed results. 

The symptoms of XYY syndrome are sometimes not noticeable until adolescence or adulthood, whereas Klinefelter shows earlier and more obvious abnormalities. When you are diagnosed or notice symptoms, here are ways you can treat and manage the disorder:

Treatment / How to get rid of XYY Syndrome

Since it is pretty much impossible to correct the chromosomes in our body, there is little to no treatment method to get rid of XYY syndrome. If patients catch onto the condition early and start therapy earlier rather than later, it will be more effective and beneficial. There are a few ways in which you can treat it through various therapy techniques

Therapy for XYY syndrome is supportive and intricately designed for each patient, as each one has different symptoms or severity of symptoms. Treatments can be effective within a few years and include:

Speech therapy 

Many XYY syndrome patients suffer with speech difficulties and delayed motor skills. These therapy sessions will help the patient weigh up their strengths and weaknesses in the speech skills and focus on improving the weaknesses. It can help a patient overcome their speech difficulty for good, or in some cases help improve certain weak areas.

Speech therapists can also provide plans for future long term improvement, which is good to practice on a daily basis to see quicker results.

Physical therapy

Physical therapy is commonly provided for XYY patients at a young age, typically toddlers. It is also known as occupational therapy and is typically for treating hypotonia. The weak muscle tone symptom is most common in young boys and physical therapy can help rebuild the muscle. 

Helping with muscle tone can help a young boy gain strength in order to take part in normal daily activities. Some XYY boys are so weak for a few early years of their life that they can find it difficult partaking in easy activities.

Therefore, physical/occupational therapy is effective and recommended for young boys with the condition to improve muscle tone. Hypotonia is commonly associated with babies with XYY syndrome as opposed to adults.

Educational therapy

Many of those with XYY syndrome develop learning difficulties alongside speech difficulties, but they are very different in regards to treatment. Educational therapy can help with learning as well as behaviour, and the therapy can be provided by school teachers. It is best that the boy is comfortable with the therapist so that they listen and are keen to improve. 

These educational therapy sessions can be provided by many professionals, from teachers, outside tutors, principals or professional therapists. Who you choose to help with treatment is down to the patients preference and who they will be keen to work with the most.

Learning and behavioural difficulties are best treated when a patient feels comfortable and relaxed. A huge part of the therapy is to help the patient become relaxed and understanding before improving their weaknesses.

For those with XYY syndrome, it is recommended to have frequent doctors appointments as well as regular therapy. Doctors’ records will help you stay on track and help maintain progress of treatment. 

As treatment methods are quite limited, we also looked into if there are any ways of preventing the disorder:

How to prevent XYY syndrome?

There is no way to prevent XYY syndrome as it is a genetic disorder. However, the above information is the best way to treat or manage the symptoms and effects it can have. Symptoms can also be reduced if the disorder is diagnosed early. 

With every medical concern comes questions, so here are few answers to questions that you may still have:


Can women get XYY syndrome?

Women cannot get or develop XYY syndrome as it is a male condition whereby a male has an extra copy of the Y (male) chromosome. However, a woman can have a very similar condition whereby they have an extra copy of the X (female) chromosome.

This condition is called Triple X Syndrome and has very similar symptoms and consequences to XYY syndrome for men. They also develop physical abnormalities and learning difficulties. 

We cover both male and female health conditions, but to read more about another male topic, Male Extra, click here

What is the gender of YY?

Males typically have two different types of sex chromosomes, labelled as XY and called the hetergametic sex. Females on the other hand, have the same sex chromosomes, labelled as XX, called the homogametic sex. 

YY are two sex chromosomes not naturally bound together for normal cells, however this is closely associated with XYY syndrome and therefore holds a male gender status. Y chromosomes are male, hence why this set of chromosomes paired together is male only. 

Can XYY syndrome sufferers have babies?

Most males with XYY syndrome have little to no difficulty with sexual reproduction and can have babies. In some cases they can be infertile for a few years of their life, but the fertility strength comes back. There has not yet been evidence to show XYY syndrome patients cannot have babies. Infertility is only in rare cases and is just as likely as being infertile from other conditions.

Is XYY a mutation?

XYY is where an extra chromosome is present and therefore, only one more than the usual amount exists. It is not said or studied to verify if XYY is a mutation nor is it definitely genetic, but it is a mutation of cells that causes the syndrome. 

Do serial killers have an extra chromosome?

This may seem like a strange question, but this is commonly asked and has been thoroughly studied. 

Research suggests that those with an extra Y chromosome do have a higher chance of committing crime, but not necessarily being a serial killer. This is commonly linked with the behavioural and learning issues XYY syndrome males have. They tend to be more aggressive and uncontrollable. This is why therapy is very important and starting therapy early is very beneficial for behaviour. 

Here are our thoughts on XYY syndrome, its symptoms and consequences:


Those with XYY syndrome often live normal lives. The symptoms are usually unrecognisable and even if they are noticeable, they are quite mild. It is a disorder only 1 in 1,000 males are born with and is unpreventable. But, if symptoms persist or intervene with normal life, there are effective treatments.

Whilst there are only therapy methods for treatment, they are highly recommended and have shown positive results. Although it can be hard to notice symptoms and get an early diagnosis of XYY syndrome, the earlier a male starts therapy the better. 

This syndrome is not a worrying condition nor one that can affect a large part of the population. It is simply a chromosome imbalance that can cause mild symptoms that are easy to live with. In some cases, the symptoms will not show and affect normal life.

If you think you have symptoms or know someone with the condition looking for help, feel free to share this on. Let us know your stories and feedback. 

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