A frequent mutation in the protein S gene results in cryptic splicing.

Protein S is a vitamin K dependent coagulation inhibitor. One of several defects in the protein S gene (PROS1) associated with hereditary deficiency is a G --> A transition at position 5 of the splice donor in intron J. Although the mutation has been reported to cause allelic exclusion, we demonstrated low amounts of alternatively spliced ectopic PROS1 transcripts in carriers of this mutation. Sequencing of mutant RNA indicated the use of a cryptic splice site upstream of the common splice donor. The use of the cryptic splice site results in the deletion of 32 nucleotides at the 3' end of exon 10. The new reading frame contains several premature termination signals.