Factor VIII gene inversions and an XbaI polymorphism: nonradioactive detection and clinical usage

To simplify molecular diagnosis among families with severe haemophilia A, digoxigenin probe-labelling and chemiluminescent detection was introduced. Sensitivity was the same as with 32P; background was lower. Of 33 previously untested families with severe haemophilia A, 15 have a factor VIII gene inversion (14 distal, one proximal). In three of the 13 families with isolated occurrence, de novo origin of the mutation was assigned to the maternal grandfather (two by XbaI linkage). Within the Seattle series, 64 (45% of 143) families with severe haemophilia A have an inversion; 15 are proximal. Fifteen patients from 12 families have had inhibitors; nine of these were > 10 Bethesda units per millilitre. All 36 mothers examined from the 43 families with isolated occurrence and nearly half (30 of 63) the daughters of an inversion carrier were carriers. Of 24 families where XbaI polymorphic analysis was performed for carrier assignment, 14 were informative. In families with severe haemophilia A, a nonradioactive, digoxygenin-labelling system facilitates both factor VIII gene inversion and XbaI polymorphism analyses by Southern blots of digested, genomic DNA samples.