Klinefelter Syndrome

What is Klinefelter Syndrome? 

Klinefelter syndrome is a relatively common genetic difference seen in approximately 1 in 600 individuals with male sex. It is characterized by the presence of an additional copy of the X chromosome (47,XXY chromosomes). Klinefelter syndrome is highly variable and, in many people, remains undiagnosed.

Common features include:

  • Delayed developmental milestones in early childhood
  • Normal intelligence with some degree of reading-based learning disability and/or ADHD
  • Low levels of testosterone causing delayed or incomplete puberty
  • An increased risk for infertility

What Causes Klinefelter Syndrome?

Individuals with Klinefelter syndrome are born with an extra X chromosome in the cells of their body. Their chromosomes or karyotype is 47, XXY compared to the most common karyotype among males of 46,XY. The extra X chromosome that is present in individuals with Klinefelter syndrome provides more genetic “instructions” than is typical in the cells of the body. This can lead to differences in health and development, which can impact various body systems. 

Klinefelter syndrome is not typically passed through families. It usually occurs due to a random event during the creation of an egg or sperm cell prior to conception. It is not caused by a parent’s actions.  

What are Symptoms of Klinefelter Syndrome?

Klinefelter syndrome varies widely among individuals. Some people have many symptoms, while others have few. Common features include:

  • Low muscle tone 
  • Delayed speech and motor milestones in early childhood 
  • Learning disabilities 
  • Behavior differences 
  • Tall stature, or being taller than expected based on family members’ heights 
  • Genital differences at birth, such as an undescended testicle 
  • Small testicles 
  • Low levels of testosterone 
  • Late or absent puberty
  • Infertility or difficulty conceiving a pregnancy

Unfortunately, we cannot predict which health findings someone may or may not have. So, it is important for all people with Klinefelter syndrome to receive regular care with a knowledgeable clinician. 

Klinefelter Syndrome & Learning

People with Klinefelter syndrome usually have normal intelligence but often face learning and behavior challenges. These can include:

  • Reading and writing difficulties, like dyslexia and language disorders
  • Attention issues and hyperactivity (ADHD)
  • Problems with organization, planning, and decision-making
  • Trouble with visual tasks, such as understanding directions and interpreting graphs
  • Autistic-like traits and difficulties with social interaction

Individuals with Klinefelter syndrome may have more autistic-like traits than others, leading to challenges in understanding and expressing social cues, like facial expressions and tone of voice. They might also find it hard to interpret other people's intentions and emotions and may be seen as shy, anxious, or socially immature.

Despite these challenges, many people with Klinefelter syndrome excel in non-verbal learning and logical tasks. They often have strengths in areas like math, problem-solving, and reasoning. This can lead to successful careers in fields such as engineering, computer science, software development, photography, auto mechanics, and laboratory work.

It is recommended that children with Klinefelter syndrome undergo a neuropsychology evaluation around the age of 6-7. This testing helps identify learning strengths and weaknesses in areas like attention, memory, language, visual reasoning, and thinking speed. Sharing these results with the child’s school can help secure appropriate academic accommodations if needed.

How is Klinefelter Syndrome Diagnosed?

Klinefelter syndrome is most often diagnosed in adolescence due to delayed puberty or in adulthood due to infertility. However, with advancements in genetic testing, more people are diagnosed with Klinefelter syndrome at a younger age. For example, Klinefelter syndrome may be diagnosed: 

  • During pregnancy or infancy due to prenatal screening or testing 
  • In childhood due to delayed developmental milestones 
  • At any age when genetic testing is completed for an unrelated reason 

How is Klinefelter Syndrome Treated?

Klinefelter syndrome treatment typically includes a combination of developmental, learning, and mental health support, as well as possible testosterone replacement therapy, and fertility and family planning considerations.

Development and Learning Support

  • Early Childhood: Developmental therapies can help children reach their milestones.
  • School Entry: A neuropsychology evaluation can identify learning strengths and weaknesses, helping to determine any needed academic support.

Mental Health Support

  • People with Klinefelter syndrome often experience high stress and may have conditions like ADHD, anxiety, or depression.
  • Support from a social worker, psychologist, psychiatrist, or therapist can be very helpful.

Testosterone Replacement Therapy

  • Puberty and Development: Testosterone is important for puberty, increasing muscle mass, deepening the voice, enlarging the penis and testicles, and developing body and facial hair.
  • Monitoring: An endocrinologist should monitor for signs of low testosterone. Blood tests can check hormone levels.
  • Treatment: If needed, testosterone replacement can help maintain muscle mass, body hair, facial hair, sex drive, erections, heart health, and bone health. It will not increase testicle size or treat gynecomastia or infertility.
  • Administration: Testosterone is usually given as a weekly injection, but other options are available. Most people will need to take it throughout their life.

Fertility & Family Planning

  • Options include fertility preservation, testicular sperm extraction (TESE), in vitro fertilization (IVF), donor sperm, and adoption.

Regular care with knowledgeable healthcare providers is crucial for managing Klinefelter syndrome effectively.

Lurie Children's Klinefelter Syndrome Program

Our Klinefelter Syndrome Program offers interdisciplinary care—spanning from prenatal consultation to young adulthood—for individuals with Klinefelter syndrome. We have a family-centered approach to care and provide coordinated expertise to address the medical, developmental, and psychosocial needs of individuals with Klinefelter syndrome and their families.  Learn more about the Klinefelter Syndrome Program

Frequently Asked Questions

Klinefelter syndrome is highly variable from person to person, and many people do not know they have Klinefelter syndrome. While people with Klinefelter syndrome may see extra doctors for their medical needs and receive extra support in school, they generally grow up to be successful in academics, careers, and personal lives. 

For more information, we recommend connecting with Living with XXY, an organization that brings together people with Klinefelter syndrome and shares real life stories in an effort to reduce social stigma and address misinformation.  

There is no cure for Klinefelter syndrome, but medical screenings and treatment are designed to identify associated health problems and manage any symptoms. For example, men with Klinefelter syndrome often cannot produce enough testosterone; testosterone can be given as a medication to maintain heart, bone, and sexual health.  

Infertility is common among men with Klinefelter syndrome meaning that most men will not be able to conceive a pregnancy with a partner through sexual intercourse. Some men can have biological children with assistance of a reproductive specialist. Additionally, there are many other ways to have a family. Some individuals may choose to consider use of a sperm donor or donor embryo, or to adopt children.