Identification of a novel mutation combination in factor XIII deficiency: genetic update to the first reported case in the United States.

A 1967 report described the first known case of congenital factor XIII (FXIII) deficiency in the United States in a male patient with a severe hemorrhagic disorder. The patient's family presented no symptoms of the disorder, but the members were found to have half the normal FXIII activity. Although the molecular basis of the disorder could not be evaluated at the time, the results suggested an autosomal recessive inherited disorder. We sequenced all of the exons and the flanking regions in the genes for the FXIII A and B subunits of the patient, his family, and 18 unrelated individuals. We report the novel combination of an Arg-to-Cys mutation at codon 78 and a G-to-C mutation at the intron 5/exon 6 splice junction in the patient's FXIIIA gene. The missense-splice junction mutation combination appears to have caused the patient's FXIIIA deficiency, because the remaining family members, who present no symptoms and have no clinical diagnoses of FXIII deficiency, have one or the other of the 2 mutations but not both. Additionally, the 18 unrelated individuals are homozygous wild type at these loci. The molecular consequences of these mutations appear to be an abnormality in protein conformation or folding and/or a reduced production of messenger RNA transcripts of varying length that likely result in a nonfunctional, unstable FXIII protein.