NONHOMOLOGOUS RECOMBINATION IN THE HUMAN GENOME - DELETIONS IN THE HUMAN FACTOR-VIII GENE

Four deletions in the human factor VIII gene have been characterized at the sequence level in patients with hemophilia A. Deletion JH 1 extends 57 kb from IVS 10 to IVS 18. Intron 13 and exon 14 are partially deleted in patients JH 7 and JH 37, with a loss of 3.2 and 2.4 kb of DNA, respectively. The 3′ deletion breakpoint of the JH 21 event resides in intron 3 and extends 5′ into intron 1, resulting in the loss of exons 2 and 3. Seven of the eight breakpoints sequenced (5′ and 3′ for each of the four deletions) occur in nonrepetitive sequence, while the 3′ breakpoint of the JH 1 resides in an Alu repetitive element. All of the deletions are the result of nonhomologous recombination. The 5′ and 3′ breakpoints of JH 1, JH 7, and JH 37 share 2- to 3-bp homologies at the deletion junctions. In contrast, two nucleotides have been inserted at the JH 21 deletion junction. Short sequence homologies may facilitate end-joining reactions in nonhomologous recombination events. © 1991.