Summary
Using polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP)
and DNA sequencing, the molecular basis of hereditary type la antithrombin III (AT
III) deficiency was disclosed in two families. One mutation was a change from T to
A in the codon of TTA for Leu 140 forming a stop codon of TAA, which was confirmed
by mutated primer-mediated PCR-HindIII digestion. The application of this method demonstrated that all four affected
members had the mutant allele in a heterozygous state and that none of unaffected
subjects had this mutation. Another mutation in the second family was a change from
C to T in the codon of CGA for Arg 197 also forming a stop codon of TGA, which was
confirmed by PCR-HaeIII digestion. Based on these, it was concluded that the two new nonsense mutations
in the AT III gene in a heterozygous state are the molecular basis of hereditary type
Ia AT III deficiency.