Klinefelter syndrome is a genetic disorder that affects people assigned male at birth (AMAB). Affected individuals possess an extra X chromosome.¹ It was recently confirmed that there is an association between Klinefelter syndrome and learning disabilities such as dyslexia. Read on to understand how these two conditions are linked.  

Understanding Klinefelter syndrome

Genetics of Klinefelter syndrome 

Everyone is born with two chromosomes that determine their sex. Sex chromosomes can either be X or Y.¹ People AMAB are usually born with one X chromosome and one Y chromosome (referred to as XY), whilst people assigned female at birth have two X chromosomes (and thus are referred to as XX). 

Individuals with Klinefelter syndrome are born with an extra X chromosome in addition to the XY chromosome, and thus are known as XXY.¹ The acquisition of an extra X chromosome is the result of a random event during conception where either the egg or sperm carry an extra X chromosome; at fertilisation, this creates the XXY pattern.² 

Given that Klinefelter syndrome is caused by random genetic events, it not considered to be a hereditary condition. However, the chances of having child with Klinefelter syndrome increases if you are an older parent.²

Incidence of Klinefelter syndrome

Whilst Klinefelter syndrome typically refers to individuals with one extra X chromosome, it is possible for people to be born with more than one extra copies of the X chromosome - but this is very rare. This creates different classes of the syndrome.²

The incidence rate of Klinefelter syndrome with one extra X chromosome is 1 in 500, two extra X chromosomes is 1 in 50,000, and three extra X chromosomes is around 1 in 85,000 to 100,000.²

Characteristics and symptoms of Klinefelter syndrome

Physical symptoms and characteristics 

The symptoms of Klinefelter syndrome may not always be obvious, meaning that affect individuals often remain undiagnosed. People with Klinefelter syndrome often live a normal life and do not notice any issues until they experience problems with fertility (a major symptom of Klinefelter syndrome).¹ 

However, some physical symptoms can manifest early in life, including delayed development in key skills such as learning to speak and walk.¹ Other symptoms include issues during puberty: individuals with Klinefelter syndrome do not produce testosterone, so puberty may stop prematurely, or not start at all. This can result in symptoms such as:¹

• Lack of body and facial hair
• Lack of a deep voice
• Small testes and penis

Kleinfelter syndrome does not typically affect intelligence, and it has been confirmed that the average IQ of individuals with Kleinfelter syndrome is the same as the average population.³ However, affected individuals often experience learning difficulties. These can be observed in childhood, and can cause issues with:³

• Reading and writing
• Mathematics
• Maintaining concentration
• Communication

The frequent co-occurrence of Klinefelter syndrome and learning difficulties such as dyslexia and attention deficit hyperactivity disorder (ADHD) suggests that they are associated in some way, leading researchers to look further into this area.⁴ 

Learning disabilities associated with Klinefelter syndrome

Dyslexia

Dyslexia is a neurological condition which affects the brain’s ability process visual information, causing difficulties with reading and spelling.⁵ Dyslexia can also cause difficulties with language, mathematics and concentration.⁵ 

Dyslexia has been found to be associated with Klinefelter syndrome; individuals with both conditions typically experience moderate to severe problems with reading, writing and mathematics.⁶ They may also find it difficult to formulate sounds and syllables. These problems arise due to dyslexia’s impact on brain development and short term memory - which translates into difficulties with the brain’s data processing.^3,5,6,8 This may affect the learning of an individual with Klinefelter syndrome and make it difficult for them to understand and follow instructions being given - especially those given verbally. 

Attention Deficit Hyperactivity Disorder (ADHD) 

Individuals with Klinefelter syndrome are at a higher risk of ADHD than the general population, with a prevalence of 63%.⁷ Rather than hyperactivity, many individuals with both Klinefelter syndrome and ADHD may display problems with concentration They may experience sensory issues and be distracted and/or bothered by background noises.⁴ 

Speech and language disorders 

Individuals born with Klinefelter syndrome often experience problems with communication, such as articulating phonetics and sounds. This can lead to them having trouble in social situations and being quieter than usual in social settings.⁴ 

Additionally, language acquisition and development tends to be delayed in Klinefelter syndrome. As a result, individuals may struggle to understand and use language - creating problems when trying to socialise with others.¹ For example, an individual with Klinefelter syndrome may take verbal expressions literally rather than figuratively. Further, they may also struggle to express themselves.⁴ 

Diagnosis and assessment

Early detection methods 

Klinefelter syndrome is difficult to detect, as symptoms are not always present or visible. It is estimated that up to 65% of individuals that may have Klinefelter syndrome are not diagnosed.⁴ If a doctor suspects Klinefelter syndrome, they may perform a physical examination and request a blood test to identify whether there is an extra X chromosome.⁹ In adulthood, Klinefelter syndrome may be suspected for if individuals are showing signs of low fertility and/or testosterone.^1,9

Evaluation of learning disabilities 

If there are any concerns about a child’s progress in school, a screening test can be carried out by the special educational needs coordinator to identify any areas a child may need more support in.¹⁰ If any concerns are raised during this screening, the child may be referred to a certified dyslexia assessor for a diagnostic assessment. This same assessment is used for adults with concerns for dyslexia. A diagnosis of dyslexia will provide an explanation for any problems with reading, writing and organising and processing information. To test for ADHD in those with Klinefelter syndrome, the individual will be referred for an assessment by a specialist.¹¹ The assessment mostly consists of interviews on certain aspects of the individual’s life.

Treatment and support

Managing Klinefelter syndrome

As a genetic disorder, Klinefelter syndrome cannot be cured. However, some symptoms can be treated. One example is hormone replacement therapy to replace testosterone.^1,4 Increased testosterone levels strengthen the bones and muscles, and can induce or restart puberty, leading to a deeper voice and body and facial hair. Testosterone supplementation has also been shown to help with learning disabilities.¹ This therapy can be delivered over the long-term and is monitored closely to ensure there are no side effects or problems as a result of the therapy. 

Psychological and social support 

Learning disabilities such as ADHD can be treated using medications that help maintain concentration.¹² However, these medications can cause side effects, so individuals will need to be closely monitored by a specialist. 

Therapy is also used to treat ADHD, as it can help individuals learn how to behave in social situations.¹² Speech and language therapy is also used for people with Klinefelter syndrome to help with language development.¹ In addition to this, specialised one-to-one support in educational settings can help individuals with learning disabilities.¹³ For example, individuals with dyslexia may meet with a specialist to work on their reading and comprehension.¹³

In more severe cases, individuals may benefit from attending a specialist school that can offer tailored support.³ There are also many support groups for individuals and families for those with Klinefelter syndrome and the learning disabilities that are present to help with living these conditions much easier, such as the Klinefelter’s Syndrome Association (KSA).

Summary

Although rare, people assigned male at birth can be born with Klinefelter syndrome, meaning they are born with an extra X chromosome. Individuals with this syndrome have a higher chance of having learning disabilities such as dyslexia and ADHD compared to unaffected individuals. Whilst there is no cure for Klinefelter syndrome or its associated learning disabilities, there is treatment and support available to help patients and their families.