Characterization of a large chromosomal deletion in the PROS1 gene of a patient with protein S deficiency type I using long PCR.

A long-PCR-based technique was developed to investigate a possible deletion in the protein S gene, PROS1, in a family with type I protein S (PS) deficiency (pedigree PS62). Long-PCR across introns produced an unexpected 2kb PCR product between exon VII and XII not seen in control individuals, in addition to the expected 2.5 kb exon VII-VIII product. This result suggested that a deletion had occurred between exons VII and XII in the PS-deficient family members. All were heterozygous for the deletion, Sequencing of the cloned 2 kb fragment gave the precise location of the breakpoints within introns 7 and 11. Significant similarity existed in both introns to repetitive sequences, e.g. Alu and Mer12, but no significant similarity was evident between the two introns themselves. The technique of long-PCR is simple and more informative than Southern blotting in detecting and characterizing large intragenic deletions.