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47, XYY

  • 47, XYY syndrome is a numerical chromosome alteration found in approximately 1 in 1000 male births. The boy or man has an additional Y chromosome, bringing the total chromosome number to 47.
  • This alteration is not inherited; occurring as a result of errors during spermatogenesis or zygote development. Although fertile, males with 47,XYY do not produce an increase in XY or YY sperm.
  • Most men with 47, XYY do not present with any clinical symptom or show any unusual clinical feature bringing into question this condition’s status as a ‘syndrome’. Growth spurts occur from the age of 2 years until puberty, producing above-average heights.
  • Diagnosis may occur incidentally from a karyotype being tested for an unrelated reason (eg.for a familial translocation), either post-natally or pre-natally.
  • Rarely, behavioural or educational problems have been associated with 47, XYY.

Clinical features

  • The lack of a clinical presentation means that at least 85% of males with 47,XYY go un-diagnosed. A small proportion however, may have some symptoms.
  • Growth occurs more rapidly than the average from the age of 2 years until puberty, producing an average final height 7cm above the expected and with a mean of 188cm. There may be a delay in the onset of secondary sexual development by approximately 6 months of age
  • Fertility is usually unaffected, but the extra Y chromosome is rarely transmitted to the offspring.
  • Mild behavioural and educational problems are more common in males with 47,XYY, There may be communication and interaction problems with a delay in speech and language development, and increased incidence of reading difficulty.

Diagnosis

  • Often the diagnosis is made prenatally as an incidental finding on karyotyping, unrelated to the reason for requesting this from amniocentesis or chorion villus biopsy (eg. in relation to a familial translocation, or to unrelated fetal abnormality).
  • Post-natally the diagnosis may also be made incidentally from karyotyping for an unrelated reason, or may be found on genetic testing in relation to tall stature and/or educational delay. (see below).

Genetic basis

  • 47, XYY is not inherited, but occurs as a random nondisjunction (failure of chromosome pair separation) event during meiosis II of spermatogenesis. The numerical chromosomal anomaly can also be generated following fertilisation by errors in mitosis.
  • Males with 47,XYY do not produce an excess of 47,XYY or 47,XXY offspring.

Clinical management

  • As 47, XYY is most commonly not presenting with a clinical problem, specific clinical management is usually not required.
  • Routine disclosure of this aneuploidy, if detected as an incidental finding, may not always be a straightforward decision, particularly if there is no phenotypic abnormality. Certainly, disclosure requires that the information be put into an appropriate perspective.
  • Rare presentations of behavioural abnormalities which place patients on the autistic spectrum may be aided with appropriate professional help.

Genetic testing

  • Following the observance of behavioural or developmental abnormalities, detection can be carried out by karyotyping (the visualisation of a patient’s chromosomes under a light microscope to observe chromosome shape and number).
  • DNA-based techniques of qfPCR (quantitative fluorescence PCR), fluorescent in situ hybridisation (FISH), or array CGH (comparative genome hybridisation) may also be used.

 

This information is intended for educational use and was current in August 2013. For clinical management, it is recommended that local guidelines and protocols are used.