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Klinefelter Syndrome

Reports from the MHC data base

Report from the Observation Chart (PDF)



Estimated occurrence

500-600 boys are born each year


These boys are born with an extra X chromosome (47,XXY). This is the chromosome arrangement found in 80 per cent of cases of KS. In the other individuals with the syndrome, there are additional extra X or Y chromosomes. As a rule, additional X chromosomes imply additional symptoms. In approximately 50% of the individuals with KS, the extra X chromosome comes from the father, and in somewhat fewer from the mother. It does not appear to make any difference to the course of the disease from which parent the extra X chromosome comes.

General symptoms

One of the results of the extra X chromosome is a disturbance in the development of the testicles. This affects production of testosterone, a hormone which controls many of the main physical properties of the male body. Testosterone levels are nearly normal until puberty, after which they decrease gradually. Physical growth: Birth size is average, but height growth proceeds faster than normal during the first years of life. Final height tends to be about 10 cm taller than expected for the family. Other anomalies include small penis, feminine distribution of fat over hips and thighs, a tendency to breast gland growth, underdeveloped musculature, osteoporosis and infertility in adulthood. Language skills may be reduced in some individuals, resulting in reading and writing difficulties. In other boys/men with KS, general intelligence and gross motor function may also be impaired. Neuropsychiatric diagnoses such as ADHD and DAMP also seem to be more common than in others.

Orofacial/odontological symptoms

The malocclusions that occur include primarily taurodontism, i.e. large teeth with small roots. One or more missing permanent teeth also seems to be a frequent occurrence, and in some studies an increased tendency towards other malocclusions, including open bite and underbite.

Orofacial/odontological treatment

  • Regular check-ups of dental and jaw development. Orthodontist should be consulted when needed.
  • It may be difficult to perform root canal work on taurodontic teeth. This makes it especially important to maintain good dental status.
  • Neuropsychiatric diagnoses may also affect the potential for providing adequate dental treatment.


  • The MHC database - The Mun-H-Center database on oral health and orofacial function in rare diseases.
  • The Documentation from the Ågrenska national competence centre for rare diseases.
Updated: 2017-03-24 10:36