Recurrent mutations in haemophilia A give evidence for CpG mutation hotspots

Abstract

Haemophilia A is a common disorder of blood coagulation caused by a deficiency of factor VIII. It is inherited as an X-linked recessive trait, and one-third of all cases are thought to result from de novo mutations. The clinical severity of haemophilia A varies markedly among different families and a subset of the patients with severe disease develop antibodies against factor VIII, called inhibitors. Because of this heterogeneity, it is likely that many different molecular lesions result in haemophilia A. Indeed, of the nine mutations described to date, all appear to be unique changes. However in this study of 83 patients with haemophilia A we have identified two different point mutations, one in exon 18 and one in exon 22, that have recurred independently in unrelated families. Each mutation produces a nonsense codon by a change of CG to TG, and each occurred de novo on the X-chromosome donated by the maternal grandfather. These observations strongly support the view that CpG dinucleotides are mutation hotspots.

Nonsense mutation in factor VIII gene of a severe haemophiliac patient with anti-factor VIII antibody

“…Anti-factor VIII antibodies (inhibitor) have been reported among patients caused by nonsense mutation in exon 18 (Higuchi et al, 1987;Matthews et al, 1987), 23 (Matthews et al, 1987), 24 (Gitschier et al, 1985;Higuchi et al, 1987) and26 (Higuchi et al, 1987) but not by nonsense mutation in exon 22 (Youssoufian et al, 1986;Higuchi et al, 1987). It has been also reported that missense mutations in exons 24 (Bernardi et al, 1987) and 26 (Gitschier et al, 1986) can cause a formation of anti-factor VIII antibodies (Table 1).…”

“…The TaqI restriction site (TCGA) containing CpG dinucleotide are frequently examined in haemophiliacs by Southern blotting. Thus far, either the CpG--,TpG mutation (Antonarakis et al, 1985;Gitschier et al, 1985;Youssoufian et al, 1986Youssoufian et al, , 1987bHiguchi et al, 1987;Matthews et aL, 1987) or CpG--+ CpA mutation (Gitschier et al, 1986;Bernaldi et aL, 1987) has been observed in exons 18, 23, 24, and 26 of factor VIII gene. CpG --, TpG change caused a nonsense mutation from CGA (Arg) to TGA (stop codon), and the CpG -, CpA change caused a missense mutation from CGA (Arg) to CAA (Gin).…”

“…The gene encodes a protein with 2,351 amino acid residues including the initiation codon (position -19). Molecular deficiencies have been reported in factor VIII by several independing groups (Antonarakis et al, 1985;Gitschier et al, 1985Gitschier et al, , 1986Youssoufian et al, 1986Youssoufian et al, , 1987a. Since the size of factor VIII gene is 186 kbp long containing 26 exons, complete sequence of the gene is not easily determined for each of the patient, and the genetic polymorphism at the various sites are analyzed as a linked marker of the genetic defect.…”

From Genotype to Phenotype - When the Parents Ask the Question

“…and moderate haemophilia A. Deletions in the factor VIII gene are reported to be associated with increased tendency for inhibitor development because of incorrect protein folding resulting in exposure of immunogenic epitopes that are usually buried within the protein core (Youssouffian et al, 1987;Gouw et al, 2007Gouw et al, , 2011. Specific mutation hotspots are 5-methylated cytosine residues which are readily deaminated to thymine (Youssoffian, 1986). These mutations usually result in introduction of premature stop codon (transition CGATGA) and, ultimately, in a truncated protein.…”

A deletion involving intron 13 and exon 14 of factor VIII gene in a haemophiliac with anti-factor VIII antibody

“…The genetic heterogeneity of haemophilia patients suggests that many different molecular alterations are involved in the resultant malfunctional factor VIII gene in haemophiliacs. Several point and deletion mutations in the factor VIII gene were observed in Caucasian population (Gitschier et al, 1985(Gitschier et al, , 1986Antonarakis et al, 1985;Youssoufian et al, 1986Youssoufian et al, , 1987aYoussoufian et al, , 1987bHiguchi et al, 1987;Bernardi et aL, 1987;Matthews et al, 1987).…”