The Canadian "National Program for hemophilia mutation testing" database: a ten-year review.

A reference genotyping laboratory was established in 2000 at Queen's University, Kingston, to provide genetic testing for Hemophilia A (HA) and B (HB) and create a Canadian mutation database. Canadian hemophilia treatment centers and genetics clinics provided DNA and clinical information from November 2000 to March 2011. The factor VIII (F8) gene was analyzed in 1,177 patients (47% of HA population) and 787 female family members and the factor IX (F9) gene in 267 patients (47% of HB population) and 123 female family members, using Southern Blot, PCR, conformation sensitive gel electrophoresis, and/or direct sequencing. The mutation detection rates for HA and HB were 91% and 94%, respectively. 380 different F8 mutations were identified: inversions of intron 22 and intron 1, 229 missense, 45 nonsense, eight deletions, 70 frameshifts, 25 splice site, and one compound mutation with a splice site and intron 1 inversion. Of these mutations, 228 were novel to the Hemophilia A Database (HADB, http://hadb.org.uk/). A total 125 different F9 mutations were identified: 80 missense, 12 frameshift, 12 splice site, nine nonsense and seven promoter mutations, three large deletions, and two compound mutations with both missense and nonsense changes. Of these mutations, 36 were novel to the International Haemophilia B Mutation database (http://www.kcl.ac.uk/ip/petergreen/haemBdatabase.html). The Canadian F8 and F9 mutation database reflects the allelic heterogeneity of HA and HB, and is similar to previously described populations. This report represents the largest and longest duration experience of a national hemophilia genotyping program documented, to date.

The mutational spectrum of type 1 von Willebrand disease: Results from a Canadian cohort study.

In order to evaluate the changes within the VWF gene that might contribute to the pathogenesis of type 1 von Willebrand disease (VWD), a large multicenter Canadian study was undertaken. We present data from the sequence analysis of the VWF gene in 123 type 1 VWD index cases and their families. We have identified putative mutations within the VWF gene in 63% (n = 78) of index cases, leaving 37% (n = 45) with no identified changes. These changes comprise 50 different putative mutations: 31 (62%) missense mutations, 8 (16%) changes involving the VWF transcriptional regulatory region, 5 (10%) small deletions/insertions, 5 (10%) splicing consensus sequence mutations, and 1 nonsense mutation. Twenty-one of the index cases had more than one putative VWF mutation identified. We were somewhat more likely to identify putative mutations in cases with lower VWF levels, and the contribution of other factors, such as ABO blood group, seems more important in milder cases. Taken as a whole, our data support a complex spectrum of molecular pathology resulting in type 1 VWD. In more severe cases, genetic changes are common within the VWF gene and are highly penetrant. In milder cases, the genetic determinants are more complex and involve factors outside of the VWF gene.

Heterogeneity of the immune response to adenovirus-mediated factor VIII gene therapy in different inbred hemophilic mouse strains.

BACKGROUND: The development of anti-factor VIII (FVIII) antibodies (inhibitors) is a critical concern when considering gene therapy as a potential treatment modality for hemophilia A. We used a hemophilia A mouse model bred on different genetic backgrounds to explore genetically controlled differences in the immune response to FVIII gene therapy. METHODS: C57BL/6 FVIII knockout (C57-FVIIIKO) mice were bred with normal BALB/c (BAL) mice, to generate a recombinant congenic BAL-FVIIIKO model of hemophilia A. Early generation adenoviral (Ad) vectors containing the canine FVIII B-domain-deleted transgene under the control of either the CMV promoter or a tissue-restricted (TR) promoter were administered to C57-FVIIIKO, C57xBAL(F1)-FVIIIKO crosses, and BAL-FVIIIKO mice. FVIII expression, inhibitor development, inflammation, and vector-mediated toxicity were assessed. RESULTS: In response to administration of Ad-CMV-cFVIII, C57-FVIIIKO mice attain 3-fold higher levels of FVIII expression than BAL-FVIIIKO. All strains injected with Ad-CMV-FVIII displayed FVIII expression lasting only 2 weeks, with associated inhibitor development. C57-FVIII-KO mice that received Ad-TR-FVIII expressed FVIII for 12 months post-injection, whereas FVIII expression was limited to 1 week in C57xBAL(F1)-FVIIIKO and BAL-FVIIIKO mice. This loss of expression was associated with anti-FVIII inhibitor development. BAL-FVIIIKO mice showed increased hepatotoxicity with alanine aminotransferase levels reaching 4-fold higher levels than C57-FVIIIKO mice. However, C57-FVIIIKO mice initiate a more rapid and effective cell-mediated clearance of virally transduced cells than BAL-FVIIIKO, as evidenced by real-time PCR analysis of transduced tissues. Overall, strain-dependent differences in the immune response to FVIII gene delivery were only noted in the adaptive response, and not in the innate response. CONCLUSIONS: Our results indicate that the genetic background of the murine model of hemophilia A influences FVIII expression levels, the development of anti-FVIII inhibitors, clearance of transduced cells, and the severity of vector-mediated hepatotoxicity.

Sustained phenotypic correction of canine hemophilia A using an adeno-associated viral vector.

Gene therapy for hemophilia A requires efficient delivery of the factor VIII gene and sustained protein expression at circulating levels of at least 1% to 2% of normal. Adeno-associated viral type 2 (AAV2) vectors have a number of advantages over other viral vectors, including an excellent safety profile and persistent gene expression. However, a major disadvantage is their small packaging capacity, which has hampered their use in treating diseases such as hemophilia A, cystic fibrosis, and muscular dystrophy, which are caused by mutations in large genes. Here we demonstrate that this can be overcome by using small regulatory elements to drive expression of a B-domain-deleted form of FVIII. The use of this vector for hepatic gene transfer in a canine model of hemophilia A resulted in the sustained (> 14 months) expression of biologically active FVIII. FVIII activity levels of 2% to 4% were achieved. These levels correlated with a partial correction in the whole-blood clotting time and cuticle bleeding time. In addition, immunoprecipitation analysis demonstrated the expression of canine FVIII of the predicted size in the plasma of injected animals. These data support the use of AAV2 vectors in human clinical trials to treat hemophilia A patients.

Aberrant splicing and premature termination of transcription of the FVIII gene as a cause of severe canine hemophilia A: similarities with the intron 22 inversion mutation in human hemophilia.

We have identified the causative mutation in the hemophilia A dog colony at Queen's University, Canada and have observed a striking similarity with the intron 22 inversion found in approximately 45% of severely affected hemophilia A patients. The canine hemophilia A phenotype arises from aberrant splicing and premature termination of transcription of the FVIII gene, resulting in a polyadenylated transcript lacking exons distal to 22 and terminating with a novel sequence element (NSE). In dogs and other species including humans, this NSE is present in low copy number. One copy of these sequences in the canine genome is within intron 22 and reveals differences in the hybridization banding patterns between normal and hemophilic DNA, suggestive of a large genomic rearrangement. The mutation mechanism may not be uncommon, as identical mutant transcripts were isolated from two hemophilia A littermates that are unrelated to the Queen's colony and from hemophiliac dogs in the colony at Chapel Hill.