Christmas disease (haemophilia B) in a girl with deletion of the short arm of one X-chromosome (functional Turner syndrome).

A I-year-old girl with severe Christmas disease and a factor IX content less than I% of normal is described. The family history was negative and coagulation studies on her relatives were normal. Genetic investigation showed an XXp-karyotype with deletion of the short arm of one X-chromosome, a cytogenetic variant of Turner syndrome. The transmission pathway of the haemophilia gene is discussed.