Identification of a new CA dinucleotide repeat in the human factor VIII gene.

We describe the identification of a new CA dinucleotide repeat marker for the diagnosis of haemophilia A carriers. The marker (CA-6) is present in intron 6 as a single copy 5 kb upstream of exon 7. Of 195 and 118 X chromosomes from normal individuals and haemophilia A patients, respectively, we observed three alleles of CA-6 with 12-14 repetitions [(CA)(12-14)]. The frequencies were 0.5% and 0% for (CA)(12), 99% and 95.8% for (CA)(13), and 0.5% and 4.2% for (CA)(14) in normals and patients respectively. We conclude that the low polymorphism of the CA-6 marker renders it less useful for the diagnosis of Chinese haemophilia A carriers.