Homozygous mutation Gly542Ser in one pedigree with congenital factor XII deficiency

Abstract

Objective To analyze the mutations of F12 gene in one pedigree with congenital factor FⅫ (FⅫ) deficiency, and investigate the molecular mechanisms of FⅫ deficiency. Methods Pedigree investigation. In February 2015, a patient with hereditary FⅫ deficiency was admitted to the Third Clinical College of Wenzhou Medical University.Activated partial thromboplastin time (APTT), prothrombin time (PT), FⅫ activity (FⅫ: C), FⅫ antigen (FⅫ: Ag) and other coagulant parameters were tested in the proband and his family members. 5′ and 3′ UTR, all exons and their exon-intron boundaries of F12 gene were analyzed by direct sequencing. The detected mutations were confirmed by reverse sequencing. The conserved amino acids were analyzed by ClustalX-2.1-win software, and four bioinformatics softwares(PolyPhen-2, PROVEAN, SIFT and MutationTaster)were also used to analyze the effect of mutations on protein function. Results The proband and her younger brother showed a markedly prolonged APTT which were 116.4 s and 101.3 s, while her father had slightly prolonged APTT, and other family members were normal. The FⅫ: C and FⅫ: Ag of family members were also decreased (the proband, 2.0% and 1.0%; her younger brother, 2.0% and 1.0%; her father, 18.0% and 13.0%). The phenotype of all members was consistent with cross-reactive material(CRM) negative. Nucleotide sequencing analysis showed that the proband and her younger brother had missense mutations in the F12 gene, including one homozygous mutation c. 1681G>A (p. Gly542Ser) and a commonly reported single nucleotide polymorphism site within the promoter region of the F12 gene (46T/T). Sequencing results from the proband's parents and son demonstrated them as carriers of a heterozygous missense mutation. The proband's husband was normal and with 46C/C in the promoter region. The ClustalX-2.1-win results indicated that the Gly542 was highly conserved among the homologousspecies.The predicting outcomes of the four bioinformatics softwares were the same, the PolyPhen-2(score 1.000) and PROVEAN(score -4.975) both declared p. Gly542Ser was a harmful mutation.The SIFT(score 0.00) and the MutationTaster (score 0.999) manifested the mutation could affect the protein funtion. Conclusions c. 1681G>A (p.Gly542Ser) in exon 14 and 46T/T were related with the significant decrease of the FⅫ level of this pedigree of hereditary FⅫ deficiency.(Chin J Lab Med, 2018, 41: 214-218) Key words: Factor Ⅻ deficiency; Pedigree; Homozygote; Mutation