Background: Hemophilia B is an X-linked recessive disorder caused by mutations in the F9 gene, causing bleeding tendency predominantly in males. The mutational spectrum of the F9 gene has not been adequately studied in Iraq.

Objectives: To detect the disease-causing variants of exons 6, 7, and 8 and immediate introns of F9 gene using Sanger sequencing among Iraqi hemophilia B patients and to correlate them with phenotypes.

Methods: Forty Iraqi hemophilia B patients were recruited for this cross-sectional study from The Hereditary Bleeding Disorder Ward in the Children Welfare Teaching Hospital, Medical City, Baghdad, between November 2021 and April 2022 using a consecutive sampling technique. Peripheral blood samples were used for sequencing exons 6, 7, and 8, which encode catalytic serine protease (SP), linker, and activation peptide domains and immediate introns of the F9 gene using Sanger sequencing.

Results: Nineteen (47.5%) patients had positive conclusive results. Fifteen unique variants were detected; 12 (80%) of them were disease-causing. Nine variants were located in the SP, one in the linker domain, and two in the splice site of intron 6. The most common pathogenic variant was the c.572G>A (p.Arg191His) on the linker domain as seen in six patients, while c.880C>T (p.Arg294Ter) and c.1358G>T (p.Trp453Leu) were the most common pathogenic variants of the SP domain as seen in two patients each. The vast majority were point mutations that are generally similar to the reported phenotype.

Conclusion: Molecular profiling of F9 gene in the current cohort confirms 12 disease-causing variants, making molecular diagnosis and genetic counseling of hemophilia B possible. It explained the discrepancy between FIX level and clinical course, and variable severity among family members. Integrating genetic data into national registries will expand the molecular database for important health conditions in Iraq, improving healthcare provision through genetic counseling, prevention, and prenatal diagnosis.