Recurrent inversion breaking intron 1 of the factor VIII gene is a frequent cause of severe hemophilia A

Germ-line origin of intron 1 inversion in two haemophilia A families

Factor VIII gene inversion of intron 1 has recently been reported to be the mutation responsible for haemophilia A in about 5% of severe cases. In our series of patients, which is made up of 77 Italian cases negative for intron 22 inversion, the mutation was found in three sporadic and in one familial patients, with an overall frequency of 5.2%. The carrier status of the patients' female relatives was assessed by mutation analysis and showed that only two-thirds of cases could be considered truly sporadic. The germ-line origin of the mutation was investigated in the two sporadic families by haplotype analysis on genomic DNA of the patients' maternal grandparents. These studies indicated that both mutation events had occurred in the germ cell lines of the patients' healthy grandfather, suggesting that, as already demonstrated for the inversion of intron 22, the male germ cell line is more susceptible to the intrachromosome recombination which leads to the inversion of intron 1.

Analysis of 18 novel mutations in the factor VIII gene

We describe 18 novel mutations, unreported in the Haemophilia A mutation Databases, that have been identified in a cohort of unrelated, Italian patients affected with haemophilia A (HA). Screening of the factor VIII gene (FVIII) was performed using denaturing high-performance liquid chromatography (DHPLC) and direct sequencing. Eight mutations were characterized as non-missense alterations, and the remaining 10 were missense mutations. Heterozygosity for the identified mutations was observed in the female relatives of patients belonging to eight families with sporadic cases. In an attempt to understand better the causative effect of the mutations and the clinical variability of the patients, missense mutation consequences were investigated for: (1) the nature of the new amino acid; (2) the location of the substituted amino acid within crystallographic and theoretical models; and (3) the degree of conservation of the native residue in factor VIII (FVIII) protein and FVIII-related protein family aligned sequences. These research tools have provided evidence that the mutations we describe involve residues that were conserved, at least in FVIII proteins, in all the species we compared.

Hemophilia and related bleeding disorders: a story of dismay and success

Known since the beginning of the first millennium, the hemophilias are among the most frequent inherited disorders of blood coagulation and definitely the most severe. In the 1970s, with the availability of concentrated preparations of the deficient coagulation factors VIII and IX and with the large-scale adoption of home treatment, hemophilia care became one of the most gratifying examples of successful secondary prevention of a chronic disease. Unfortunately, in the early 1980s it was recognized that factor concentrates prepared from plasma pooled from thousands of donors transmitted the hepatitis and the human immunodeficiency viruses. The scientific community reacted promptly to the devastation brought about by hepatitis and AIDS. The last 15 years of the second millennium have witnessed the development of methods that, when applied during concentrate manufacturing, inactivate viruses escaping the screening procedures. The adoption of these measures has reduced dramatically the risk of transmission of bloodborne infections. The production of recombinant factors and their availability for patients' treatment epitomize progress in hemophilia care through DNA technology. Methods based on the polymerase chain reaction (PCR) have unraveled an array of gene lesions associated with hemophilia, permitting improved secondary control of the disease through carrier detection in women from affected families and prenatal termination of their affected male infants. This article will review the aforementioned areas of progress and discuss unresolved problems (such as treatment of patients with antibodies, the risk of new infectious complications, and the issue of secondary tumors). Hopes and expectations for further improvement in the third millennium and particularly the prospects of hemophilia cure though gene replacement therapy will also be mentioned.

Haemophilias A and B

The haemophilias are inherited disorders in which one of the coagulation factors is deficient. Although deficiencies of factor VIII (haemophilia A) and factor IX (haemophilia B) are well recognised, von Willebrand's disease is much more common. Rare defects can occur in any of the coagulation factors. In the past, men with haemophilia were likely to die in their youth. With advances in diagnosis, and especially with development of safe and effective treatment, affected individuals can now look forward to a normal life expectancy. Complications of the disorder, particularly the development of antibodies that make treatment ineffective, and of treatment, such as transfusion-transmitted infections, have taken a severe toll on these patients. The future holds the realistic possibility of gene therapy. However, we must not forget that haemophilia is a worldwide disorder that requires significant economic resources not available for the majority.

Thirty-four novel mutations detected in factor VIII gene by multiplex CSGE: modeling of 13 novel amino acid substitutions

Detection of causal mutations is required for genetic counseling. Molecular modeling combined with patients' phenotype provides significant insight into structure-function relationship of factor (F)VIII molecule. Our objective was to identify defects in the gene of FVIII by a sensitive and simple scanning technique with high throughput in order to study molecular mechanisms by which novel amino acid substitutions may lead to hemophilia A. A cohort of 81 families with mild, moderate and severe hemophilia A negative in intron 22 inversion was studied. For detection of mutations in the FVIII gene a conformation sensitive gel electrophoresis (CSGE) was modified by multiplexing. Thirteen novel amino acid substitutions were studied by molecular modeling and a correlation with the cross-reactive material (CRM) phenotype was performed. In 74 families, 59 different mutations were detected. Six different mutations were recurrent in 21 unrelated families. Thirty-four novel mutations included 19 point mutations, four small insertions, nine small deletions and two complex mutations. Thirteen novel amino acid substitutions occurred at residues conserved in FVIII orthologs. Five of them were associated with a discrepancy between FVIII activity and antigen; another five with CRM reduced phenotype and one with undetectable FVIII antigen. Multiplexing of the CSGE significantly increased its throughput without substantial loss of sensitivity. Molecular modeling suggested mechanisms by which substitutions at residues 382 and 569, located outside the proposed FIXa-binding region, may influence FVIII/FIXa interaction. His2155 was predicted to participate in FVIII/VFW binding.

Genotype and phenotype of haemophilia A in Thai patients

To study genotype and phenotype correlation of haemophilia A in Thai patients, molecular defects of the factor VIII (FVIII) gene were examined and their correlation with clinical phenotypes were evaluated. The molecular pathologies of FVIII in Thai patients were found to be heterogeneous. The most common mutation was FVIII intron 22 inversion accounting for about 30% of the severe cases while gene deletion was rare. Sixteen point mutations were identified, comprising two nonsense mutations (R-5X and R1966X), five missense mutations (T233I, D542Y, G1850V, W2229S and G2325C), five nucleotide deletions (1145delT, 1187-8delACAC, 1191-4delA, 1458delGA and 1534delA), three nucleotide insertions (1439-41insA, 1934insTA and 2245insACTA) and one splicing defect (IVS15+1G>T). Nine mutations (T233I, D542Y, 1145delT, 1458delGA, 1534delA, 1934insTA, W2229S, 2245insACTA and G2325C) were novel, firstly identified in Thai patients. The genotypes were found to correlate with clinical phenotypes in a majority of cases. However, in five patients the molecular defects did not correlate with clinical severity and FVIII:C level. Cellular and molecular mechanisms were proposed to be responsible in amelioration of clinical severity caused by deleterious mutations. Carrier detection by direct mutation analysis was also demonstrated.

High throughput mutation screening of the factor VIII gene (F8C) in hemophilia A: 37 novel mutations and genotype-phenotype correlation

Hemophilia A (HEMA) is an X-linked bleeding disorder caused by mutations in the factor VIII gene (F8C). Molecular genetic testing for the factor VIII gene is challenging due to its large size. Here we present results of high throughput mutation scanning based on Southern blot analysis and direct sequencing of all PCR amplified coding exons and the exon-intron boundaries of the factor VIII gene. The results of mutation analysis on 89 hemophiliac males showed presence of a disease-causing mutation in 80 individuals (90%, 95% CI of 82%-95%). Seven out of nine mutation-negative individuals were severe cases of hemophilia A with < 1% factor VIII protein in the blood. The correlation of phenotype with genotype as observed in this study was not absolute. This finding is supported by similar observations in the international database for hemophilia A mutations (HAMSTeRS). This issue raises the importance of genotypes at other loci that can act as modifiers for the phenotype. Thirty-four novel mutations and three novel substitutions for previously reported amino acid residues were identified in this series of 80 mutations. The mutations cover the full spectrum including rearrangements, deletions, frameshift, and point mutations. The novel missense mutations require careful evaluation. Prediction of a mutation as the disease-causing allele was made from the nature of the substitution and the degree of conservation of the mutated amino acid among species that have diverged in evolution. In some cases segregation analysis of the mutation with disease condition was performed when other family members were available.