Mosaicism in men in hemophilia: is it exceptional? Impact on genetic counselling.

Haemophilia A is an X-linked bleeding disorder caused by a wide range of mutations in the factor VIII (F8) gene . About one third [1] of cases are due to a mutation. The majority are thought to occur in a single germ cell but some, occurring during early de novo embryogenesis, produce a germline and/or somatic mosaic. In haemophilia, somatic mosaicism has been generally observed in women and seems to represent a fairly common event . We report here a case of exceptional mosaicism in the asymptomatic maternal grandfather of [2] a haemophilia A patient.