Cis-Segregation of c.1171C>T Stop Codon (p.R391*) in SERPINC1 Gene and c.1691G>A Transition (p.R506Q) in F5 Gene and Selected GWAS Multilocus Approach in Inherited Thrombophilia

Abstract

Inherited thrombophilia (e.g., venous thromboembolism, VTE) is due to rare loss-of-function mutations in anticoagulant factors genes (i.e., SERPINC1, PROC, PROS1), common gain-of-function mutations in procoagulant factors genes (i.e., F5, F2), and acquired risk conditions. Genome Wide Association Studies (GWAS) recently recognized several genes associated with VTE though gene defects may unpredictably remain asymptomatic, so calculating the individual genetic predisposition is a challenging task. We investigated a large family with severe, recurrent, early-onset VTE in which two sisters experienced VTE during pregnancies characterized by a perinatal in-utero thrombosis in the newborn and a life-saving pregnancy-interruption because of massive VTE, respectively. A nonsense mutation (CGA > TGA) generating a premature stop-codon (c.1171C>T; p.R391*) in the exon 6 of SERPINC1 gene (1q25.1) causing Antithrombin (AT) deficiency and the common missense mutation (c.1691G>A; p.R506Q) in the exon 10 of F5 gene (1q24.2) (i.e., FV Leiden; rs6025) were coinherited in all the symptomatic members investigated suspecting a cis-segregation further confirmed by STR-linkage-analyses [i.e., SERPINC1 IVS5 (ATT)_5-18, F5 IVS2 (AT)_6-33 and F5 IVS11 (GT)_12-16] and SERPINC1 intragenic variants (i.e., rs5878 and rs677). A multilocus investigation of blood-coagulation balance genes detected the coexistence of FV Leiden (rs6025) in trans with FV HR2-haplotype (p.H1299R; rs1800595) in the aborted fetus, and F11 rs2289252, F12 rs1801020, F13A1 rs5985, and KNG1 rs710446 in the newborn and other members. Common selected gene variants may strongly synergize with less common mutations tuning potential life-threatening conditions when combined with rare severest mutations. Merging classic and newly GWAS-identified gene markers in at risk families is mandatory for VTE risk estimation in the clinical practice, avoiding partial risk score evaluation in unrecognized at risk patients.

Keywords: F5; FV Leiden; GWAS; SERPINC1; cis-segregation; crossing-over; inherited thrombophilia.

Figure 1

(a) Full pedigree of the original family. Black symbols refer to thrombotic subjects carrying the combined AT-FV Leiden defect (i.e., SERPINC1-F5 mutations). Grey symbols refer to thrombotic subjects in the absence of any identified defect. The asterisk indicates an asymptomatic carrier of a single F5 p.R506Q defect. The triangle symbol indicates aborted fetus. Dashed frame indicates subfamily described in Figure 1b. (b). Extended pedigree of the previous investigated family [2]. This is part of the full pedigree shown in Figure 1a (dashed frame). The different symbols are specified in figure legend (bottom left of the figure). The triangle symbol indicates aborted fetus. Strike-through symbols indicate dead individuals.

Figure 1

(a) Full pedigree of the original family. Black symbols refer to thrombotic subjects carrying the combined AT-FV Leiden defect (i.e., SERPINC1-F5 mutations). Grey symbols refer to thrombotic subjects in the absence of any identified defect. The asterisk indicates an asymptomatic carrier of a single F5 p.R506Q defect. The triangle symbol indicates aborted fetus. Dashed frame indicates subfamily described in Figure 1b. (b). Extended pedigree of the previous investigated family [2]. This is part of the full pedigree shown in Figure 1a (dashed frame). The different symbols are specified in figure legend (bottom left of the figure). The triangle symbol indicates aborted fetus. Strike-through symbols indicate dead individuals.

Figure 2

Sequence analysis of SERPINC1 gene showing: p.R391* STOP-codon (upper panel); p.Q337Q synonymous variant (middle panel); intronic (IVS 6–7) C > G variant (rs677) (lower panel).