Two genetic defects in a patient with complete deficiency of the b- subunit for coagulation factor XIII

A genomic DNA obtained from a female patient with complete b-subunit deficiency was examined by Southern blotting analysis and in vitro amplification. Nucleotide sequence analysis showed that adenosine-4161 at the acceptor splice junction of intron A/exon II was deleted in half of the amplified DNAs, resulting in a loss of the obligatory AG splicing sequence. The absence of adenosine-4161 was confirmed by cleavage with TaqI endonuclease of the amplified DNAs. Moreover, sequence analysis showed that guanosine-11499 coding for Cys 430 (TGC) in exon VIII was replaced by thymidine in half of the amplified DNAs, resulting in an amino acid change to Phe (TTC) and the destruction of a disulfide bond in the seventh Sushi domain. This mutation was also confirmed by cleavage with MboII endonuclease. Thus, the proband turned out to be a compound heterozygote of two separate defective alleles. Although half of the amplified DNAs for exon VIII of her daughter or son were cleaved by MboII, those for intron A were not cleaved by TaqI. The replacement of guanosine-11499 by thymidine in their exon VIII has also been confirmed by sequence analysis, indicating that they are heterozygous for one normal and one defective allele.