Female hemophilia A heterozygous for a de novo frameshift and a novel missense mutation of factor VIII

Background: Hemophilia A (HA) is an X-chromosome-linked recessive disorder. Aim: We report the case of a female HA patient with a moderate decrease of factor (F) VIII activity and antigen (FVIII:C 3.4%, FVIII:Ag 4.2%) and severe bleeding symptoms. Methods: The patient's father had mild FVIII deficiency (FVIII:C 6.9%, FVIII:Ag 7.4%), and her mother had normal FVIII activity. The von Willebrand disease antigen and von Willebrand factor ristocetin cofactor activity were normal in all family members. The genomic DNA was extracted from the peripheral blood lymphocytes of the patient and her family members. Long-distance polymerase chain reaction (PCR) was employed to screen for the intron 22 inversion of the FVIII coding gene (F8). The F8 coding sequence was amplified with PCR and sequenced with an automatic sequencer. Results: Two heterozygous mutations were identified in the patient: one a substitution of nucleotide 5981T by C that leads to a missense mutation Leu1975Pro, and the other an insertion of an 'A' between nucleotides 3637 and 3638 (3637_3638insA) that shifts the reading frame and predicts a premature stop codon downward. The mutation Leu1975Pro was identified in the father's F8; however, 3637_3638insA was a de novo mutation that occurred in the patient's maternal-derived F8. Real-time PCR was applied to analyze the level of ectopically F8 gene transcripts in the peripheral lymphocytes of family members. The ectopic transcripts of F8 of the patient were less abundant than the normal control (patient:normal control ratio 0.67), whereas her parents showed no significant difference from the normal control. Conclusion: The FVIII deficiency of the HA patient resulted from a de novo occurrence of a frameshift 3637_3638insA in her maternal-derived F8 and a novel missense mutation Leu1975Pro inherited from her father.