OBJECTIVETo investigate the phenotype and genotype defect characteristics of a Chinese patient with hereditary factor XI deficiency.

METHODSThe activated partial thromboplastin time (APTT), prothrombin time (PT), FXI activity (FXI:C) of the proband and his relatives were measured by a clotting method using automatic coagulation analyzer. FXI antigen (FXI:Ag) was assayed by enzyme-linked immunosorbent assay (ELISA). Fifteen exons of the F11 gene were amplified by PCR and sequenced. Pymol software was used to analyze the novel mutations.

RESULTSThe APTT of the proband was significantly prolonged (70.3 s, reference 34.5 s) with decreased FXI activity (6%, reference 50%-150%) and FXI antigen (1.9%, reference 50%-150%). The FXI activity and FXI antigen of his son was 31% and 39%, respectively. Two heterozygous F11 mutations were identified in the proband, which included a G to T substitution at nucleotide 1296 in exon 11 resulting in substitution of glycine by valine at codon 400 (p.Gly400Val) and a A to T substitution at nucleotide 1691 in exon 14 resulting in substitution of arginine (AGA) by a termination codon (TGA) at codon 532 (p.Arg532Ter). Analysis using Pymol indicated that the number of hydrogen bonds has changed, which led to a transformation of the structure of the FXI protein. The son of the proband was found to be heterozygous for the c.1296G to T (p.Gly400Val) mutation. NM_13142 c.1691A to T (p.Arg532Ter) is a novel mutation based on HGMD professional 2016.4. Based on 2015 Guidelines of ACMG, it is PVS1 (very strong pathogenicity).

CONCLUSIONThe compound heterozygous mutations of F11 NM_13142 c.1296G to T (p.Gly400Val) and F11 NM_13142 c.1691A to T(p.Arg532Ter) probably underlies the FXI deficiency in the proband.