Haemophilia A: carrier detection by DNA analysis

Insights into the Molecular Genetic of Hemophilia A and Hemophilia B: The Relevance of Genetic Testing in Routine Clinical Practice

Hemophilia A and hemophilia B are rare congenital, recessive X-linked disorders caused by lack or deficiency of clotting factor VIII (FVIII) or IX (FIX), respectively. The severity of the disease depends on the reduction of coagulation FVIII or FIX activity levels, which is determined by the type of the pathogenic variants in the genes encoding the two factors (F8 and F9, respectively). Molecular genetic analysis is widely applied in inherited bleeding disorders. The outcome of genetic analysis allows genetic counseling of affected families and helps find a link between the genotype and the phenotype. Genetic analysis in hemophilia has tremendously improved in the last decades. Many new techniques and modifications as well as analysis softwares became available, which made the genetic analysis and interpretation of the data faster and more accurate. Advances in genetic variant detection strategies facilitate identification of the causal variants in up to 97% of patients. In this review, we discuss the milestones in genetic analysis of hemophilia and highlight the importance of identification of the causative genetic variants for genetic counseling and particularly for the interpretation of the clinical presentation of hemophilia patients.

F8 genetic analysis strategies when standard approaches fail

Haemophilia A is a common X-linked recessive disorder caused by mutations in F8 leading to deficiency or dysfunction of coagulant factor VIII (FVIII). Despite tremendous improvements in mutation screening methods, in a small group of patients with FVIII deficiency suffering from haemophilia A, no DNA change can be found. In these patients, analysis reveals no causal mutations even after sequencing the whole coding region of F8 including the flanking splice sites, as well as the promoter and the 3’ untranslated region (UTR). After excluding the mutations mimicking the haemophilia A phenotype in interacting partners of the FVIII protein affecting the half life and transport of the protein, mutations or rearrangements in non-coding regions of F8 have to be considered responsible for the haemophilia A phenotype.

In this review, we present the experiences with molecular diagnosis of such cases and approaches to be applied for mutation negative patients.