Spectrum of factor IX gene mutations causing haemophilia B from India

Molecular analysis of severe hemophilia B in Indian families: Identification of mutational hotspot and novel variants

INTRODUCTION

Hemophilia B is associated with molecular heterogeneity, with more than 1200 unique variants in the F9 gene. We hereby describe the mutational spectrum of severe hemophilia B patients presenting in a tertiary-care center in India.

METHOD

DNA was extracted from peripheral blood samples of 35 diagnosed severe hemophilia B patients belonging to 32 families, and were subjected to Sanger sequencing. Determination of the effect of novel variants on the protein structure and correlation between genotype and phenotype was attempted using in-silico tools.

RESULTS

Twenty-seven different mutations were detected in 30 probands, including 20 known and 7 novel variants. Also, we found one suspected case of whole gene deletion. The serine peptidase domain harbored most of the variants (48.1%). Inhibitory antibodies were found in two patients.

CONCLUSIONS

This study provides a comprehensive mutational spectrum and mutation screening strategy by Sanger sequencing of F9 gene in severe hemophilia B patients, in a resource-constraint setting.

Comprehensive analysis of phenotypes and genetics in 21 Chinese families with haemophilia B: characterization of five novel mutations

Molecular characterization of haemophilia B (HB) at the factor IX gene (F9) is essential to establish diagnosis, confirm genotype-phenotype correlations and to advise in genetic counselling. This study aimed to identify the causative mutations in 21 Chinese families with HB and to analyse the association of these mutations with clinical phenotype. Phenotypic analyses were performed using one-stage assay for factor IX (FIX) activity (FIX: C) and enzyme-linked immunosorbent assay for FIX antigen (FIX: Ag). Direct sequencing of the F9 gene was carried out. For those suspected to have a large deletion, multiplex ligation-dependent probe amplification (MLPA) was performed. Predicting the causal impact of new changes was studied by bioinformatics approaches. We also assessed the effect of the F9 mutations on the FIX protein structure and function. Causative mutations were detected in all study patients. There were 14 point mutations, three small deletions, one large deletion and one small in-frame duplication that together comprised a total of 19 unique variants, of which five were novel. The structural and functional defects of novel missense and in-frame deletion/duplication mutations were demonstrated by bioinformatics approaches. The 12 missense mutations include five purely quantitative mutations, five predominantly qualitative abnormalities and two combined defects. Our data confirmed the genetic heterogeneity of the F9 mutations. Quantitative missense mutations were found to be in different regions of precursor FIX compared with qualitative and combined ones.

Efficient detection of factor IX mutations by denaturing high-performance liquid chromatography in Taiwanese hemophilia B patients, and the identification of two novel mutations

Hemophilia B (HB) is an X-linked recessive disorder characterized by mutations in the clotting factor IX (FIX) gene that result in FIX deficiency. Previous studies have shown a wide variation of FIX gene mutations in HB. Although the quality of life in HB has greatly improved mainly because of prophylactic replacement therapy with FIX concentrates, there exists a significant burden on affected families and the medical care system. Accurate detection of FIX gene mutations is critical for genetic counseling and disease prevention in HB. In this study, we used denaturing high-performance liquid chromatography (DHPLC), which has proved to be a highly informative and practical means of detecting mutations, for the molecular diagnosis of our patients with HB. Ten Taiwanese families affected by HB were enrolled. We used the DHPLC technique followed by direct sequencing of suspected segments to detect FIX gene mutations. In all, 11 FIX gene mutations (8 point mutations, 2 small deletions/insertions, and 1 large deletion), including two novel mutations (exon6 c.687-695, del 9 mer and c.460-461, ins T) were found. According to the HB pedigrees, 25% and 75% of our patients were defined as familial and sporadic HB cases, respectively. We show that DHPLC is a highly sensitive and cost-effective method for FIX gene analysis and can be used as a convenient system for disease prevention.