Prothrombin Saint-Denis: a natural variant with a point mutation resulting in Asp to Glu substitution at position 552 in prothrombin.

A new prothrombin variant, with a point mutation at nucleotide 20 029 resulting in Asp 552 to Glu substitution (prothrombin numbering), has been identified in a male newborn. Plasma prothrombin level was <3%, 16% and 60% when measured by clotting, chromogenic and immunological assays respectively. The substitution did not affect the rate of prothrombin conversion to thrombin but altered thrombin activity.