FACTOR-XIII(A CALGARY) - A CANDIDATE MISSENSE MUTATION (LEU667PRO) IN THE BETA-BARREL 2 DOMAIN OF THE FACTOR-XIII(A) SUBUNIT

Molecular analysis performed on a Canadian family with congenital factor XIII deficiency revealed a homozygous missense mutation (Leu667Pro) in exon 14 of the A subunit gene in three affected siblings. The mutation results from a T-to-C transition at nucleotide position 2087 and generates a new Mspl restriction site. Digestion of an amplified fragment containing exon 14 with this restriction enzyme enabled the heterozygous allele to be identified in both parents (who were third cousins) and three other family members. SSCP analysis detected no additional mutations in the coding or consensus splice sequences of the A subunit gene. The mutant nucleotide substitution was absent in 60 normal alleles and 10 unrelated patients with XIII(A) deficiency. Leu667 is located in the carboxyl terminal beta barrel 2 domain of the A subunit molecule. Computer modelling based on 3D crystallographic data predicts that the mutant protein has aberrant folding and is likely to be rapidly degraded following translation.