Hereditary factor XIII deficiency: report of four families and definition of the carrier state.

Definition of the carrier state of hereditary factor XIII deficiency was attempted by a study of four unrelated families with patients affected by the disease. Ten homozygotes, 14 obligatory carriers and 20 suspected carriers were available for determination of plasma factor XIII subunits A and B levels (by electroimmunoassay) and for assay of factor XIII enzymatic activity (by 14C-putrescine incorporation into casein). Evaluation of the ability of seven variables related to these tests to discriminate between healthy controls and obligatory carriers disclosed that two variables related to the enzymatic assay classified correctly 92.9% of the carriers and 73.3% of the controls, whereas the variables related to subunit A had a lower discriminative ability. Entering both enzymatic and immunologic variables into the discriminant function did not improve the result of the former. A classification function was established from which the posterior probability of suspected carriers can be determined by measuring the incorporation of 14C-putrescine into casein at 90 min after adding the labelled amine.