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

Abstract

Deficiency of coagulation factor IX encoded by F9 gene (OMIM*300746) causes abnormality in the blood coagulation cascade and prolonged bleeding, known as hemophilia B (Christmas disease) (OMIM #306900). It is a rare X-linked disease, affecting around 1 in 25,000 to 30,000 live births. 1 It is diagnosed on the basis of clinical manifestations such as joint hemarthrosis, pronged bleeding; biochemical profiling of factor IX level, and family history. Hemophilia B patients are generally male with severe clinical manifestations; however, 40% to 60% of female carriers have some bleeding problems. 2 Based on residual plasma FIX activity, it is divided into severe (factor IX level <1%), moderate (factor IX level 1%-5%) and mild (factor IX level >5%-40%). 3 Molecular analysis in the F9 gene has been an area of extensive research that led to the identification of many mutations within the F9 gene. There has always been a growing interest in highlighting the differences pertaining to hemophilia mutational spectra in various populations. Genetic screening performed on familial cases reported a wide range of genetic mutations, showing large molecular heterogeneity. Till now, more than 1200 unique genetic variants have been identified in the F9 gene (www.f9-db.eahad. org). These include point mutations, small insertions/deletions, large deletions, duplications, complex rearrangements, and neutral polymorphisms. 3 Variation in mutation spectrum of F9 gene across the different populations has also been observed. [4][5][6] Molecular analysis using PCR and Sanger sequencing along with dosage analysis for detection of large deletions/duplications enables mutation detection in approximately 92% of patients. 3 This also helps in the prediction