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Congenital knee dislocation in a 49,XXXXY boy.
  1. R H Sijmons,
  2. A J van Essen,
  3. J D Visser,
  4. M Iprenburg,
  5. G F Nelck,
  6. M L Vos-Bender,
  7. B de Jong
  1. Department of Medical Genetics, University of Groningen, The Netherlands.


    We report on a 12 year old mentally retarded boy who presented at birth with bilateral knee dislocations, dislocation of the right hip, and general joint laxity. Cytogenetic studies showed a 49,XXXXY karyotype. Hyperlaxity of joints is known to occur in 49,XXXXY patients, but congenital knee dislocation has not been reported. Rarely in 49,XXXXY and 49,XXXXX syndromes Larsen-like features may be seen. Patients with congenital joint dislocation or laxity, combined with other malformations, especially if psychomotor development is delayed, should be karyotyped to exclude chromosomal abnormalities.

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