What are common symptoms of Klinefelter syndrome (KS)?

Because XXY males do not really appear different from other males and because they may not have any or have mild symptoms, XXY males often don't know they have KS.1,2

In other cases, males with KS may have mild or severe symptoms. Whether or not a male with KS has visible symptoms depends on many factors, including how much testosterone his body makes, if he is mosaic (with both XY and XXY cells), and his age when the condition is diagnosed and treated.

KS symptoms fall into these main categories. 

Many physical symptoms of KS result from low testosterone levels in the body. The degree of symptoms differs based on the amount of testosterone needed for a specific age or developmental stage and the amount of testosterone the body makes or has available.

During the first few years of life, when the need for testosterone is low, most XXY males do not show any obvious differences from typical male infants and young boys. Some may have slightly weaker muscles, meaning they might sit up, crawl, and walk slightly later than average. For example, on average, baby boys with KS do not start walking until age 18 months.3

After age 5 years, compared with typically developing boys, boys with KS may be slightly:

  • Taller
  • Fatter around the belly
  • Clumsier
  • Slower in developing motor skills, coordination, speed, and muscle strength

Puberty for boys with KS usually starts normally. But because their bodies make less testosterone than non-KS boys, their pubertal development may be disrupted or slow. In addition to being tall, KS boys may have:

  • Smaller testes and penis
  • Breast growth (about one-third of teens with KS have breast growth)
  • Less facial and body hair
  • Reduced muscle tone
  • Narrower shoulders and wider hips
  • Weaker bones, with a greater risk for bone fractures
  • Decreased sexual interest
  • Lower energy
  • Reduced sperm production

An adult male with KS may have these features:

  • Infertility. Nearly all men with KS are unable to father a biologically related child without help from a fertility specialist.4
  • Small testes, with the possibility of testes shrinking slightly after the teen years5
  • Lower testosterone levels, which lead to less muscle, hair, and sexual interest and function
  • Breasts or breast growth (called gynecomastia)

In some cases, breast growth can be permanent, and about 10% of XXY males need breast reduction surgery.6

Most males with KS have normal intelligence quotients (IQs)7,8 and successfully complete education at all levels. (IQ is a frequently used intelligence measure but does not include emotional, creative, or other types of intelligence.) Between 25% and 85% of all males with KS have some kind of learning- or language-related problem, which makes it more likely that they will need some extra help in school. Without this help or intervention, KS males might fall behind their classmates as schoolwork becomes harder.

KS males may experience some of the following learning- and language-related challenges9:

  • A delay in learning to talk. Infants with KS tend to make only a few different vocal sounds. As they grow older, they may have difficulty saying words clearly. It might be hard for them to distinguish differences between similar sounds.
  • Trouble using language to express their thoughts and needs. Boys with KS might have problems putting their thoughts, ideas, and emotions into words. Some may find it hard to learn and remember some words, such as the names of common objects.
  • Trouble processing what they hear. Although most boys with KS can understand what is being said to them, they might take longer to process multiple or complex sentences. In some cases, they might fidget or “tune out,” because they take longer to process the information. It might be difficult for KS males to concentrate in noisy settings. They might also be less able to understand a speaker’s feelings from speech alone.
  • Reading difficulties. Many boys with KS have difficulty understanding what they read (called poor reading comprehension). They might also read more slowly than other boys.

By adulthood, most males with KS learn to speak and converse normally, although they may have a harder time doing work that involves extensive reading and writing.

Many of the social and behavioral symptoms in KS may result from the language and learning difficulties. For instance, boys with KS who have language difficulties might hold back socially and could use help building social relationships.

Boys with KS, compared with typically developing boys, tend to be:

  • Quieter
  • Less assertive or self-confident
  • More anxious or restless
  • Less physically active
  • More helpful and eager to please
  • More obedient or more ready to follow directions

In the teenage years, boys with KS may feel their differences more strongly. As a result, these teen boys are at higher risk of depression, substance use, and behavioral disorders. Some teens might withdraw, feel sad, or act out their frustration and anger.

Most men with KS have lives similar to those of men without KS. They successfully complete high school, college, and other levels of education. They have successful and meaningful careers and professions. They have friends and families.

Contrary to research findings published several decades ago, males with KS are no more likely to have serious psychiatric disorders or to get into trouble with the law.10

Males with poly-X Klinefelter syndrome have more than one extra X chromosome, so their symptoms might be more pronounced than in other males with KS. In childhood, they may have seizures, crossed eyes, constipation, and recurrent ear infections. Poly-KS males might also show slight differences in other physical features.11

Some common additional symptoms for several poly-X Klinefelter syndromes are listed in the following sections.


  • Long legs
  • Little body hair
  • Lower IQ, averaging 60 to 80 (normal IQ is 90 to 110)
  • Leg ulcers and other vascular disease symptoms
  • Extreme shyness, but also sometimes aggression and impulsiveness

48,XXXY (or tetrasomy)

  • Eyes set further apart
  • Flat nose bridge
  • Arm bones connected to each other in an unusual way
  • Short height
  • Fifth (smallest) fingers curving inward (clinodactyly)
  • Lower IQ, averaging 40 to 60
  • Immature behavior

49,XXXXY (or pentasomy)

  • Low IQ, usually between 20 and 60
  • Small head
  • Short height
  • Upward-slanted eyes
  • Heart defects, such as when the chambers do not form properly12
  • High feet arches
  • Shyness but friendliness
  • Difficulty with changing routines


  1. Abramsky, L., & Chapple, J. (1997). 47, XXY (Klinefelter syndrome) and 47,XYY: Estimated rates of and indication for postnatal diagnosis with implications for prenatal counselling. Prenatal Diagnosis, 17(4), 363-368.
  2. Visootsak, J., Aylstock, M., & Graham, J.M. Jr. (2001). Klinefelter syndrome and its variants: An update and review for the primary pediatrician. Clinical Pediatrics (Phila), 40(12), 639-651.
  3. Simpson, J.L., de la Cruz, F., Swerdloff, R.S., Samanga-Sprouse, C., Skakkebaek, N.E., Graham, J.M. Jr., et al. (2003). Klinefelter syndrome: Expanding the phenotype and identifying new research directions. Genetics in Medicine, 5(6), 460-468.
  4. Plotton, I., Brosse A., & Lejeune, H. (2010). Is it useful to modify the care of Klinefelter's syndrome to improve the chances of paternity? Annales d'endocrinologie (Paris), 71(6), 494-504. French.
  5. Smyth, C.M., & Brenner, W.J. (1998). Klinefelter syndrome. Archives of Internal Medicine,158(12), 1309-1314.
  6. Bock, R. (1993). Understanding Klinefelter syndrome: A guide for XXY males and their families (Adolescence section). NIH Pub. No. 93-3202. Office of Research Reporting. Retrieved June 5, 2012 from NICHD.
  7. Geschwind, D.H., & Dykens, E. (2004). Neurobehavioral and psychosocial issues in Klinefelter syndrome. Learning Disabilities Research & Practice, 19(3), 166-173.
  8. Linden, M.G., Bender, B.G., & Robinson, A. (2002). Genetic counseling for sex chromosome abnormalities. American Journal of Medical Genetics, 110(1), 3-10.
  9. Visootsak, J., & Graham, J.M. Jr. (2009). Social function in multiple X and Y chromosome disorders: XXY, XYY, XXYY, and XXXY. Developmental Disabilities Research Reviews, 15(4), 328-332.
  10. Ratcliffe, S. (1999). Long-term outcome in children of sex chromosome abnormalities. Archives of Diseases in Children, 80(2), 192-195.
  11. Linden, M.G., Bender, B.G., & Robinson, A. (1995). Sex chromosome tetrasomy and pentasomy. Pediatrics, 96(4 Pt 1), 672-682.
  12. Kassai, R., Hamada, I., Furuta, H., Cho, K., Abe, K., Deng, H. X., & Niikawa, N. (1991). Penta X syndrome: A case report with review of the literature. American Journal of Medical Genetics, 40(1), 51-56.
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