Identification of a new haemophilia B M case produced by a mutation located at the carboxy terminal cleavage site of activation peptide

Summary. We describe a novel point mutation due to C→G transversion at nucleotide 20518 in the exon VI of factor IX gene, resulting in the substitution of glycine (GGG) for arginine (CGG) at position 180 in the polypeptide. This point mutation was found in a patient with a haemophilia B M variant. We designated the altered factor IX produced by this new mutation as factor IX Madrid . This mutation blocks the cleavage site involved in the release of the activation peptide at Arg180–Val181. It also abolishes the Aval site (CTCGGG) in exon VI, which can be directly detected with the enzymatic DNA amplification technique (PCR) and offers the possibility of direct analysis in carrier and prenatal diagnosis in kindreds with this mutation.