Homozygosity for the protein S Heerlen allele is associated with type I PS deficiency in a thrombophilic pedigree with multiple risk factors.

The multifactorial character of thrombotic disease is shown in a Spanish pedigree in which the propositus, with recurrent deep vein thrombosis, inherited the factor V R/Q506 mutation, the prothrombin 20210G/A variant and type III Protein S deficiency. Among 14 relatives carrying one or two of these three risk factors, thrombosis is present in a heterozygote for R/Q506 and in another for 20210G/A, who also had slightly positive antiphospholipid antibodies. Type I PS deficiency was also found in a young asymptomatic woman. PROS1 analysis showed coexistence of type III and type I PS deficiency to be associated with heterozygosity and homozygosity, respectively, for the P460 or PS Heerlen allele of the S/P460 variant. Analysis of PS values in this and other pedigrees segregating this variant revealed that not only free but also mean total PS levels are slightly but significantly lower in the SP460 heterozygotes than in the SS460 homozygotes. These findings strongly suggest a role of the P460 variant in the expression of the PS deficient phenotype.