The Study on Genetic Defects in a Hypofibrinogenemia Pedigree

Objective: Congenital hypofibrinogenemia is a hereditary disease, caused byheterozygous mutations of fibrinogen alpha chain (FGA), fibrinogen beta chain (FGB)and fibrinogen gamma chain (FGG) genes which code for fibrinogen (Fg), leading tosignificant low level of plasma Fg. Mutation types include missense, nonsense, splicing,promoter, small insertion and deletion mutation. These mutations can affecttranscription, mRNA (messenger RNA) processing, translation, posttranslationalprocessing, peptide folding, chain assembing, and exporting from the hepatocyte or thestability of the mature protein. Congenital hypofibrinogenemia is a rare disease, oftenfound in European region. So far only a few gene mutations have been determined inChinese with the disease. These include ΑαⅣ S2+1G＞C, γAsp320Gly, γAsp316His,BβGly419Val and γThr277Arg. We identified a hypofibrinogenemia of a Chinesepedigree, and the etiology is unknown. The purpose of this study is to study the geneticdefects of this hypofibrinogenemia pedigree, and further reveal pathogenetic mechanismof congenital hypofibrinogenemia.Methods: Peripheral blood was collected from the family members. Activatedpartial thromboplastin (APTT), thrombin time (TT), prothrombin time (PT), D-dimer,fibrin degradation products (FDP), and antithrombin Ⅲwere tested. The activity ofplasma Fg were analyzed by Solidification method. Genomic deoxyribo nucleic acid(DNA) was extracted from peripheral blood, and the sequences of all the exons of threefibrinogen genes FGA, FGB and FGG were amplified by polymerase chain reaction(PCR). The amplification products were purify, and then analyzed by direct sequencingto search for mutations in the genes.Results: The Fg levels of the proband, his sister and one of the brothers weresignificantly reduced to0.84g/L,0.87g/L,0.61g/L, respectively. PT and TT of theproband and his sister were extended, with PT of15.8sec and15.5sec (normal range 11-14.5sec), respectively, and TT of30sec and29.7sec (normal range14-21sec),respectively. D-dimer, FDP and antithrombin III were all in the normal range. The Fglevels of proband’s daughter, son and niece were normal. The genetic analysis onproband revealed three homozygous mutations in FGA, FGB, FGG: FGA g.1674A> T,FGA g.3271C> T and FGG g.4931A> T. Such mutations were also found in the otherpatients and normal individuals in the pedigree. Three heterozygous mutations FGGg.7925C>T, FGG g.8208G>A and FGG g.7933G>A were also detected.Conclusion: The three homozygous mutations were also found in the otherpatients and normal individuals of the pedigree, therefore were not the disease-causingmutations. Whereas, the three heterozygous mutations may be the candidates of thepathogenic mutations responsible for this familial hypofibrinogenemia, pending furtherconfirmation with whole genome sequencing and functional experiments.