FV gene mutations and hemostatic parameters in FV Leiden pseudohomozygotes. (A) Top: F5 gene mutations preventing the expression of the non-Leiden FV allele in pseudohomozygous probands P1-P5. Italics, nucleotide changes; FS, frame shift; X, stop codon. Amino acid changes are indicated with the one-letter code. The large exon 13 is not drawn to scale. Bottom: FV activity (FVc) and antigen (FVag) levels (normal range, 80%-120%) and normalized APC sensitivity ratio (nAPC-sr). APC resistance is defined by an APC-sr less than 0.84; nAPCsr range of FV Leiden homozygotes 0.35 to 0.45. Mutations and patients are aligned. (B) Distribution of the endogenous thrombin potential (ETP) determined in the presence of APC in individuals with normal FV genotype (n = 11), FV Leiden heterozygotes (n = 12), FV Leiden homozygotes (n = 32), and FV Leiden pseudohomozygotes (n = 6). Genotype groups were compared with the Mann-Whitney Wilcoxon test. The horizontal lines indicate the means in the respective genotype groups. FVL stands for Factor V Leiden.