Congenital Fibrinogen Deficiencies: Not So Rare.

Congenital fibrinogen deficiencies (CFDs), traditionally considered rare monogenic disorders, are now recognized as more prevalent and genetically complex than previously thought. Indeed, the symptoms manifested in CFD patients, such as bleeding and thrombosis, are likely to result from variation in several genes rather than solely driven by variants in one of the three fibrinogen genes, FGB, FGA, and FGG. This review highlights recent advances in understanding the genetic causes of CFD and their variability, facilitated by the growing use and availability of next-generation sequencing data. Using gnomAD v4.1.0. data, which includes more than 800,000 individuals, we provide updated global prevalence estimates for CFDs based on frequencies of predicted deleterious variants in FGB, FGA, and FGG. Recessively inherited fibrinogen deficiencies (homozygous genotypes) could be present in around 29 individuals per million, while dominantly inherited deficiencies (heterozygous genotypes) may be present in up to 15,000 per million. These increased estimates can be attributed to the inclusion of broader, more diverse genetic datasets in the new version of gnomAD, thus capturing a greater range of rare variants and homozygous cases.