Summary
We report the application of single-stranded conformation polymorphism (SSCP) analysis
to the screening of 15 functionally important Protein S (PS) gene (PSα) regions (4.243
Kb) in 6 unrelated families with PS deficiencies. Direct sequencing of the fragments
with altered migration patterns led to the identification of the corresponding molecular
alterations. A missense mutation, G to T transversion at codon Cys598, and two different
alterations, leading either to allelic exclusion, or premature termination of the
protein translation: a G to A transition at codon Trp465 and a 1 nt (T) insertion
at codon 265, were identified. The 1 nt insertion was observed in three apparently
unrelated families but with a common geographical origin and the mutated allele was
undetectable in platelet mRNAs of affected individuals. Family analysis confirmed,
in each case, a perfect cosegregation of the mutation with the PS deficiency. We conclude
that these alterations represent the causative mutations.