Klinefelter's syndrome

Congenital chromosome condition in which men have two or more X-chromosomes (e.g. XXY or XXXY instead of XY). Nearly all men with the Klinefelter syndrome are infertile.



Additional X-chromosome

Normally, men have 1 X-chromosome and 1 Y-chromosome (XY). Men with the Klinefelter's syndrome have in addition to the Y-chromosome 2 or more X chromosomes (XXY, XXXY, …).


Klinefelter's is usually the result of a division error of the chromosomes in the reproductive cell of the mother or father.  

For instance, a sperm cell will get both an X and a Y chromosome, or an egg cell both X's.

If a XY-sperm cell fertilises an egg cell, or if an XX egg cell merges with a sperm cell with a Y chromosome, it will result in the chromosome pattern 47, XXY.


Nearly all men with Klinefelter's are infertile. At a young age it usually goes unnoticed. 

The disorder is often diagnoses by accident, e.g. as a result of fertility problems. 


The major symptoms of Klinefelter's syndrome are:

  • Absence of sperm cells
  • Infertility 
  • Impaired testicular development during puberty
  • Delayed puberty or delayed sexual development
  • Testosterone deficiency resulting in reduced development of male sex characteristics and reduced bone density
  • Children with Klinefelter's syndrome are usually a little bit taller than their peers. 

In some rare case we see delayed language and speech development or distorted motor development.

Risk factors and genetics

  • Occurs only in men (sex chromosome disorder)
  • Congenital, but not hereditary


A testosterone treatment can be beneficial for the development of male sex characteristics and increased bone density.

Possibilities for a fertility treatment will be examined in consultation with the fertility centre. 

Tests and diagnosis

In case of this disorder, or if we suspect this disorder, we will perform one or several of the following examinations:

  • Chromosome examination
  • Blood test to determine the amount of testosterone 
  • Physical examination of the testicles and other sex characteristics
  • Bone densitometry
  • Klinefelter's syndrome can already be diagnosed during pregnancy based on a CVS test or an amniocentesis. 
Last edit: 27 October 2020