Background: Hemophilia B (HB) is an X-linked bleeding disorder resulting from coagulation factor IX defects. Over 3,000 pathogenic, HB-associated mutations in the F9 gene have been identified. We aimed to investigate the role of F9 variants in 150 HB patients using sequencing technology.
Methods: F9 gene sequences were amplified from peripheral blood-derived DNA and sequenced on an Applied Biosystems (ABI) 3500 Sanger sequencing platform. Functional and structural predictions of mutant FIX were analyzed.
Results: Among 150 HB patients, 102 (68%), 30 (20%), and 18 (12%) suffered from severe, moderate, and mild HB, respectively. Genetic analysis identified 16 mutations, including 3 novel mutations. Nine mutations (7 missense and 2 stop-gain) were found to be pathogenic. Only 3 mutations (c.127C＞T, c.470G＞A, and c.1070G＞A) were associated with different severities. While 2 mutations were associated with mild HB cases (c.304C＞T and c.580A＞G), 2 (c.195G＞A and c.1385A＞G) and 3 mutations (c.223C＞T, c.1187G＞A, and c.1232G＞A) resulted in moderate and severe disease, respectively. Additionally, 1 mutation each was associated with mild-moderate (c.*1110A＞G) and mild-severe HB disease (c.197A＞T), 4 mutations were associated with moderate-severe HB cases (c.314A＞G, c.198A＞T, c.676C＞T, and c.1094C＞A). FIX concentrations were lower in the mutated group (5.5±2.5% vs. 8.0±2.5%). Novel p.E66D and p.S365 mutations were predicted to be pathogenic based on changes in FIX structure and function.
Conclusion: Novel single nucleotide polymorphisms (SNPs) largely contributed to the pathogenesis of HB. Our study strongly suggests that population-based genetic screening will be particularly helpful to identify risk prediction and carrier detection tools for Indian HB patients.
Keywords: F9 gene; Hemophilia B; India; Missense mutation; Stop-gain mutation.