Chromosomal mosaicism in a case of Klinefelter's syndrome associated with thalassaemia

Summary An unusual chromosomal constitution, XXxY/XXY , with both mosaicism and a probable partial deletion of an ‐X‐chromosome is reported in a case of Klinefelter's syndrome associated with severe thalassaemia. Evidence is submitted for regarding the association as coincidental. The literature regarding chromosomal constitution in Klinefelter's syndrome is reviewed and the possible mechanisms by which the constitution might have arisen in this patient are discussed. This work was carried out whilst holding a grant from the British Empire Cancer Campaign. I am grateful to Dr E. R. Huehns for some of the haematological investigations and for helpful discussion and to Mrs Joy Delhanty for assistance with the skin culture. I would also like to thank Prof. L. S. Penrose and Dr T. A. J. Prankerd for reading the manuscript and the latter for permission to study this case.