BackgroundHaemophilia A (HA) is a rare bleeding disorder caused by variants in F8. Although traditional mutational analyses have identified numerous pathogenic variants, the aetiology of HA in certain patients remains unclear. Furthermore, female patients with severe HA are rare.AimTo investigate the molecular defects underlying severe HA in two patients and provide personalised reproductive interventions for their families.MethodsTwo patients diagnosed with severe HA without other clinical phenotypes were enrolled in the study. A combination of whole‐exome sequencing, real‐time quantitative polymerase chain reaction and long‐read sequencing (LR‐sequencing) was performed to reveal the molecular defects of them, followed by the application of different reproductive intervention strategies.ResultsProband 1, a 29‐year‐old man with FVIII activity of 0.8%, did not exhibit common F8 variants, including Inv1 or Inv22, in the coding region. However, he carried a rare maternal novel inversion on ChrX:154148973_154170321, spanning approximately 21.345 Kbp, with breakpoints in introns 13 and 14 of F8. Finally, the couple of Proband 1 opted for assisted reproductive technology using preimplantation genetic testing and successfully conceived. Proband 2, a 20‐year‐old female with severe HA and FVIII activity of 0.6%, carried inv22 of F8. Further investigation combining whole exome sequencing (WES) and pedigree analysis revealed that she carried a maternal cross‐deletion encompassing exons 1–22 of F8, FUNDC2, BRCC3 and CLIC2, along with a de novo missense variant c.5852T>C (p.Leu1951Ser) on her paternal X‐chromosome. Chromosome X‐inactivation (XCI) analysis demonstrated a highly skewed inactivation of the maternal X chromosome, with a ratio of 98:2. Subsequently, prenatal diagnosis confirmed that the third child in this family did not carry any of the F8 variants present in Proband 2.ConclusionOur findings provide novel insights into the genetic aetiology of HA and emphasise the importance of a definitive diagnosis in guiding genetic counselling and personalised reproductive interventions for affected individuals and their families.
