Summary
A patient with a severe bleeding tendency and hypoprothrombin-emia (Factor II activity
2%, Factor II antigen 5%) was screened for the presence of alterations in his prothrombin
gene. Direct sequencing of PCR fragments derived from the coding and flanking regions
of the prothrombin gene, revealed that the patient was homozygous for an A ⟶ G substitution
in exon 3. This substitution predicts the replacement of Tyr 44 (TAC) by Cys (TGC)
in the prothrombin molecule. Both parents were found to be heterozygous for the same
mutation. Further family studies revealed complete cosegregation of the mutation with
the prothrombin deficiency. Only the five homozygous brothers and sisters of the propositus
were clinically affected (severe hemorrhages including epistaxis, soft tissue, muscle
and joint bleedings in all, and severe hemorrhages in the two women). The bleeding
tendency therefore seems to inherit as an autosomal recessive trait.