Wide spectrum of F9 variants in hemophilia B families from the Portuguese population

Introduction: Hemophilia B is an X-linked bleeding disorder caused by molecular defects in the Factor IX gene (F9), leading to either deficiency or functional abnormality of Factor IX. Actual data indicate a high heterogeneity of variants in F9. Over 1000 different variants have been reported, including pathogenic single nucleotide variants (SNPs), indels and complex variants. Materials and Methods: 86 index patients and 313 relatives were studied. F9 variant analysis was performed from total genomic DNA by PCR followed either by SSCP and DNA sequencing or direct DNA sequencing. When no variant was detected by sequencing, F9 analysis by MLPA was performed. Segregation studies were performed in each family. Results: Overall, 52 different F9 variants have been identified, including 49 SNPs or small indels, a gross duplication (exons 2-6) and two deletions of the entire gene. Ten of the variants had been firstly reported by us and three are novel: c.391+5G>T; c.432T>G, p.(Phe144Leu) and c.749C>A, p.(Ala250Glu). This approach allowed establishing the carrier state of over 300 women and 12 prenatal diagnoses were performed. Conclusions: The spectrum of F9 variants identified in the Portuguese population significantly overlaps that observed in other populations. Identification of F9 gene variants in patients allows genotype-phenotype correlations and carrier detection, as well as prenatal diagnosis. Sanger sequencing of the coding region and adjacent intronic sequences of F9 still remains a valid and effective tool for the molecular study of hemophila B, providing information for appropriate genetic counseling and new insights regarding the molecular basis of the pathology.