XYY syndrome

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The XYY (also known as XYY trisomy , Diplo-man syndrome , Supermaskulinitäts syndrome , Jacobs syndrome , Diplo-Y syndrome , YY syndrome or Polysomy Y called) is a numerical chromosomal aberration ( aneuploidy ) of the sex chromosomes. People with this syndrome are phenotypically male, but, unlike the usual male karyotype (46, XY), have an additional Y chromosome (47, XYY). There can also be other X chromosomes , so that karyotypes such as (48, XXYY) or (maximum) (52, XXXXXXYY) are possible. Since the individuals are practically completely symptom-free, the “syndrome”, the name of which is therefore also criticized, has no clinical relevance.


The first scientifically proven case was published in August 1961 by Avery A. Sandberg's group in The Lancet . It was an accidental find; the affected man was phenotypically completely normal.


In contrast to other syndromes , such as Klinefelter syndrome or Turner syndrome , XYY syndrome was not named after its discoverer. This is explained by the fact that from around 1960 onwards the nomenclature no longer provided for naming according to the first descriptor, but according to the chromosomal structure, in this case 47, XYY. Nevertheless, it is sometimes referred to as Jacobs syndrome according to Patricia A. Jacobs , the general first person to describe gender chromosis aberrations, who also examined the XYY syndrome in 1965.

Symptoms and course

Physical symptoms

Some symptoms of this syndrome are more common, but are by no means necessarily present:

  • This includes an increased average height, which is caused by accelerated growth in early childhood. People are around seven to eight centimeters taller than the predicted height. As a result, they appear rather slim, because their body weight does not increase to the same extent. Because of this habitus , Marfan's syndrome is often wrongly assumed first.
  • In many cases, severe acne is reported in adolescence, which can well extend into adulthood.
  • Some studies found elevated testosterone levels .

Other physical abnormalities that are more common in men with XYY syndrome than in the rest of the population include: B .:


The prognosis for people with this syndrome is good. Their life expectancy is not affected and their fertility is usually given, albeit slightly reduced by some symptoms (e.g. undescended testicles).


One can often read of decreased fertility . This is not the case. Although the men have a reduced sperm quality with a high proportion of immature sperm ( spermatogonia ), the mature sperm are, however, developed as usual, albeit in fewer numbers. You have a very low risk (less than 1%) of passing on the extra Y chromosome as it is lost during spermatogenesis . Therefore, apart from the largely lacking "disease value" of this phenomenon, there is no reason for affected men not to reproduce, as was recommended by doctors in the 1960s and 1970s.


There are major misunderstandings in this area that are only slowly disappearing despite being cleared up.

Wrong assumptions

XYY men are cognitively retarded

This is a prejudice. The intelligence of men is subject to the same fluctuations as that of the average population. Differences can only be determined in a direct comparison with unaffected siblings. However, this is not serious, since these small differences in IQ do not allow any conclusions to be drawn about cognitive abilities.

This misunderstanding was probably caused by statistical errors . Almost only those people were tested for XYY syndrome who had already shown abnormalities. A preselection was already included in this sample . This assumption hides the fact that the majority of men with the XYY syndrome remain normal and untested.

XYY men are criminal sociopaths

This prejudice has existed since its discovery, but when an article by Johannes Nielsen's working group in The Lancet was about analyzes of prison inmates in 1968 , this article in particular (and the reporting in the mass media) made this false assumption Anchored in people's memories.

The number of men with the syndrome in prisons as a percentage of the total number of inmates was found to be 25 to 60 times greater than the rest of the population. What got lost in the media, however, was the fact that the sample was small and only contained two XYY men. It is not possible to draw conclusions about the totality from such a random sample because the statistical error is too large. Larger studies in the last few decades then no longer showed any correlation between XYY and antisocial behavior.

The image of the criminal XYY man with a tendency to sexual crimes was propagated in the film Alien 3 , among others .

Actual differences

However, there are phenotypic differences between men with and without XYY syndrome. XYY men can have the following problems, presumably due to the increased testosterone level:

  • The development of boys is somewhat delayed in their youth compared to girls. This is reinforced by the additional Y chromosome, which is why XYY boys, for example, have slightly poorer fine motor skills .
  • Due to the increased testosterone value, special behavior patterns are more likely to be expressed. This can manifest itself in a more short-tempered temperament , an attention deficit, or increased restlessness. The variance of the expression is high, however, so that no reliable diagnosis can be made here either.


The prevalence worldwide is between 1: 590 (Northern Europe) and 1: 2000 (USA), although there are too few sufficiently large studies to allow a precise statement.

root cause

Scheme of meiosis - development of aneuploid germ cells through non-disjunction in the second meiosis

During spermatogenesis , i.e. the formation of male germ cells , meiosis II leads to a non-disjunction event on the Y chromosome. The two chromatids do not separate from each other. This creates sperm with the karyotype (23, X), which is the usual one, with a ratio of 50%. But 25% also sperm with the karyotype (24, YY) and 25% sperm without gonosomes . If a (24, YY) sperm fuses with a (23, X) egg cell , the zygote is (47, XYY).

If there is nondisjunction of the homologous chromosomes (meiosis I) as well as one of the sister chromatids (meiosis II) in the egg cell as well as in the sperm, the maximum numerical chromosome aberration is (52, XXXXXXYY). However, this is very unlikely.


  • MR. Wiedemann, J. Kunze, J. Spranger: Atlas of the clinical syndromes. 5th edition. Schattauer FK Verlag, Stuttgart 2001, ISBN 3-7945-2043-2 .
  • A. Emery: Emery and Rimoin's Principles and Practices of Medical Genetics. (3 volumes) 4th edition. Churchill Livingstone, London 2001, ISBN 0-443-06434-2 .

Web links

Individual evidence

  1. Sandberg, Avery A .; Koepf, George F .; Ishihara, Takaaki; Hauschka, Theodore S .: An XYY human male . In: Lancet . 278, No. 7200, Aug 26, 1961, pp. 488-489. doi : 10.1016 / S0140-6736 (61) 92459-X . PMID 13746118 .
  2. Gerd Plewig , Albert M. Kligman: Acne and Rosacea, Springer-Verlag, 2013, p. 351 [1]
  3. ^ Q. Shi, RH Martin: Aneuploidy in human spermatozoa: FISH analysis in men with constitutional chromosomal abnormalities, and in infertile men. In: Reproduction. (2001); Vol. 121, pp. 655-666. Archived copy ( memento of the original from January 13, 2005 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.reproduction-online.org
  4. J. Nielsen, T. Tsuboi, G. Sturup, D. Romano: XYY chromosomal constitution in criminal psychopaths. In: Lancet. (1968); Vol. 7, p. 576.
  5. Telfer, Mary A .; Baker, David; Longtin, Lucien: YY syndrome in an American Negro . In: Lancet . 291, No. 7533, January 13, 1968, p. 95. doi : 10.1016 / S0140-6736 (68) 90107-4 . PMID 4169701 .
  6. Telfer, Mary A .; Baker, David; Clark, Gerald R .; Richardson, Claude E .: Incidence of gross chromosomal errors among tall criminal American males . In: Science . 159, No. 3820, March 15, 1968, pp. 1249-50. doi : 10.1126 / science.159.3820.1249 . PMID 5715587 .