Molecular genetic analysis of severe protein C deficiency

Abstract

Severe protein C deficiency is a rare, early onset, venous thrombotic condition that is inherited as an autosomal recessive trait. The protein C (PROC) genes of nine unrelated individuals with severe protein C deficiency were sequenced yielding a total of 13 different lesions. Eight of these were novel, including a gross gene deletion, three missense mutations, two micro-deletions, a splicing mutation and a single base-pair substitution in the HNF-3 binding site in the PROC gene promoter. Evidence for the pathogenicity of the mutations detected was obtained by molecular modelling, in vitro splicing assay and reporter gene assay. Neither the plasma protein C activity level nor the nature of the PROC gene lesions detected were found to be a good prognostic indicator of the age of onset or clinical severity of thrombotic symptoms. Other factors may thus complicate the relationship between genotype and clinical phenotype. Indeed, in two patients, the inheritance of either one or two Factor V Leiden alleles in addition to two PROC gene lesions could have served to precipitate the thrombotic events. No association was however apparent between clinical severity and the possession of a particular promoter polymorphism genotype. Despite the absence of a clear genotype-phenotype relationship, the molecular genetic analysis of the severe recessive form of protein C deficiency potentiates both the counselling of affected families and the provision of antenatal exclusion diagnosis.

Identification of an intronic regulatory element in the human protein C ( PROC) gene

“…Thus the upstream portion of the core promoter contains two overlapping hepatocyte nuclear factor (HNF)-3 sites (Spek et al 1995b) and one HNF-1/HNF-6 site (Berg et al 1994;Spek et al 1998a) in close proximity to the transcription start sites (Spek and Reitsma 1999). The analysis of naturally occurring promoter mutations has served to confirm that these liver-specific transcription factor binding sites are functional in vivo (Berg et al 1994;Spek et al 1995bSpek et al , 1998aTsay et al 1996;Miao et al 1996;Millar et al 2000). In addition to these upstream elements, sequences within the 5' UTR are also required for full basal promoter activity.…”

“…Inherited protein C deficiency constitutes a risk factor for thrombotic disease: homozygous or compound heterozygous individuals suffer from massive disseminated intravascular coagulation or neonatal purpura fulminans (Branson et al 1983;Seligsohn et al 1984;Marlar et al 1989) whilst heterozygotes are at risk of venous thrombosis (Allaart et al 1993;Reitsma 1997). Screening of the PROC genes of affected individuals has identified numerous disease-causing mutations, some of which occur in the upstream promoter region and act by disrupting the regulation of PROC gene expression (Reitsma et al 1995 and http://www.xs4all.nl/~reitsma/Prot_C_home.htm; Spek and Reitsma 1999;Millar et al 2000). Polymorphisms in the upstream promoter and 5' untranslated region have also been shown to be associated with inter-individual differences in the plasma level of protein C (Spek et al 1994;Scopes et al 1995;Spek et al 1995a;Aiach et al 1999).…”

Genetic risk factors of venous thrombosis

“…Loss-of-function mutations in the PC gene results in deficiency of PC, which is considered a well-established cause of VTE. Similarly to AT deficiency, the molecular abnormalities underlying PC deficiency have been elucidated in many families and are highly heterogeneous Aiach et al 1995;Reitsma 1997;Millar et al 2000). PC deficiency is classified in type I (low plasma concentrations of both functional and immunologic PC) and type II (low plasma levels of functional protein with normal antigen levels).…”

Skin Necrosis and Purpura Fulminans in Children With and Without Thrombophilia—A Tertiary Center's Experience

“…PC homozygous deficiency was first described by Griffin's group [4] as an autosomal dominant disorder. Severe genetic PC deficiency, occurring at a rate of 1/1,000,000 live births, may be caused by homozygous or compound heterozygous mutations in the PC gene, which is located on chromosome 2q14-21 and which consists of 9 exons and 8 introns [5][6][7]. PS is a physiologic inhibitor of coagulation acting as a cofactor of activated PC (APC) that inhibits factors Va and VIII.…”

“…Acquired PF may result from conditions that trigger acute reduction of PC activity [2], such as warfarin-induced skin necrosis that typically appears at the onset of warfarin therapy in patients with heterozygous PC or PS deficiency [5]. Any skin necrosis in a child with PC deficiency requires replacement therapy with fresh-frozen plasma (FFP) or PC concentrate (along with anticoagulants) in order to suppress the intense activation of coagulation [12,16].…”