Genetic and Clinical Characteristics of Russian Patients with Congenital Factor V Deficiency.

Congenital factor V (FV) deficiency is a rare autosomal recessive bleeding disorder caused by pathogenic variants in F5 gene and characterized by heterogeneous clinical manifestations. The aim of this study was to define the mutational spectrum of F5 in Russian patients with congenital FV deficiency. We analyzed 16 unrelated patients with different disease severity and 9 relatives from five families. All functionally relevant regions of F5 were examined by Sanger sequencing. Multiplex ligation-dependent probe amplification (MLPA) was used to detect large deletions and duplications. Whole-genome sequencing and functional cDNA analysis were performed in selected cases. This study represents the first description of the F5 mutational spectrum in a Russian cohort. We identified 12 novel variants and demonstrated the functional effect of two previously unreported variants located outside canonical splice-site dinucleotides, leading to aberrant splicing. Notably, the proportion of variants undetectable by routine diagnostic approaches was higher than that reported in other populations. No clear genotype-phenotype correlation was observed. Despite the limited sample size, our findings expand current knowledge of the molecular basis of congenital FV deficiency and may improve genetic diagnostics in Russia.