We show that a point mutation causing hemophilia B changes the amino acid at position -4 in the propeptide region of factor IX from an arginine to a glutamine, which results in the expression of a stable longer protein with 18 additional amino acids of the N-terminal propeptide region still attached.
By amplification and direct sequencing, 51 single base substitutions were found in the transcribed sequence of the factor IX genes of patients from 50 distinct families with hemophilia B.
However, a synonymous mutation c.459G>A (Val107Val) was clinically reported to result in mild haemophilia B (FIX coagulant activity 15%-20% of normal).
Polymerase chain reaction (PCR) amplification and direct sequencing of all regions of likely functional significance- the coding regions, promoter, the 5' UTR, the splice junctions and parts of the 3' UTR of the factor IX gene was done in 18 families carrying a severe form of hemophilia B.
Factor IXAlabama is a variant factor IX molecule responsible for a clinically moderate form of hemophilia B. Twenty-five kilobases (kb) of the variant gene, including seven exons coding for the structural protein, were cloned and characterized.
As models we selected F9 nonsense mutations with readthrough-favorable features affecting the pre-peptide and pro-peptide regions of coagulation factor IX (FIX), which cause hemophilia B (HB).
This patient also developed an antibody to factor IX during replacement therapy, which suggests that deletion of the factor IX gene is not necessary for development of the antibody in hemophilia B patients.
One family affected with the hemophilia B Leyden phenotype was found to have a specific single-base mutation (G----A) at nucleotide -6 of the factor IX gene.
Modification of the N-terminus of human factor IX by defective propeptide cleavage or acetylation results in a destabilized calcium-induced conformation: effects on phospholipid binding and activation by factor XIa.
We conclude that this method can be advantageously used for diagnosis purposes in a routine laboratory involved in haemophilia B diagnosis and report nine previously undescribed haemophilia B families with their factor IX mutation.
This patient also developed an antibody to factor IX during replacement therapy, which suggests that deletion of the factor IX gene is not necessary for development of the antibody in hemophilia B patients.
To define the precise genetic defects of hemophilia B of Chinese origin, we have used the polymerase chain reaction (PCR) combined with direct sequencing to analyze the amplified DNA fragments containing the entire coding regions and their flanking introns of the factor IX gene from 6 affected individuals.