fibrinogen is a 340-kd glycoprotein , one of the critical proteins of the blood coagulation and platelet aggregation ( 1 ) .
it is composed of six polypeptide chains , (  ,  , )2 , which are held together by disulfide bonds and organized in a symmetrical dimeric fashion ( 1 ) . until now , a variety of mutations in each of the fibrinogen chain genes have been reported in more than 465 families all over the world , with a-chain mutation being the most common form , followed by -chain mutation ( 2 ) .
the first report was a(517 - 522)delins31 , designated as " fibrinogen seoul " in a 7-yr - old girl associated with amyloidosis ( 3 ) .
the second was  ala341asp , which was designated as " fibrinogen seoul i " , in a 66-yr - old woman with peripheral artery obstructive disease ( 4 ) .
the third was a   gln328pro , which was designated as " fibrinogen seoul ii " , in a 51-yr - old man who suffered from recurrent myocardial infarction ( 5 ) .
here we describe a -chain fibrinogen variant ( fibrinogen yecheon ) , which is a point mutation from t to c in the 1,007th nucleotide of the fgg gene , resulting in a methionine ( met)-to - threonine ( thr ) substitution at the 310th residue in the carboxy - terminal region of the fibrinogen -chain .
this is the fourth report of  met310 to thr substitution in the world , and the first in korea . as for genetic dysfibrinogenemia , this is the fourth case report in korea .
a 20-yr - old male patient with past medical history of bleeding tendency in neonate period visited the department of otorhinolaryngology for a preoperative evaluation for operation of chronic maxillary sinusitis .
he reported a family history of easy bruisability of his father and conductive hearing difficulty after meningitis in childhood .
no laboratory abnormalities indicating coagulation defect had been detected after birth . in the preoperative evaluation ,
the patient had normal blood counts and serum chemistry test results . however , the initial coagulation screening showed prolonged prothrombin time ( pt , 24.5 sec ; normal 10.4 - 12.5 sec ) and activated partial thromboplastin time ( aptt , 47.3 sec ; normal , 26.0 - 41.0 sec ) .
the bleeding time was normal ( 2 min and 30 sec ; normal , 1 - 5 min ) .
the fibrinogen degradation product ( fdp ) and d - dimer were within normal ranges .
other coagulation tests were normal ( table 1 ) . on the other hand , plasma fibrinogen activity of the subject examined using the clauss method was lower than the detection limit ( < 25 mg / dl ; normal , 140 - 460 mg / dl ) , while the antigen level measured by fibrinogen elisa was normal ( 437 mg / dl ) .
all exons , exon - intron boundaries , and promoter regions of the fibrinogen a ( fga , genbank m64982 ) , b ( fgb , genbank m64983 ) , and  ( fgg , genbank m10014 ) chain genes were amplified and sequenced .
pcr and direct sequencing revealed that only the patient in his family was heterozygous for a point mutation in the fgg gene .
the mutation was a mutation substituting the 310th codon atg ( met ) to acg ( thr ) , ( c.1007t > c ) ( fig .
we designated the patient 's abnormal fibrinogen as " fibrinogen yecheon " , naming after the local city where he and his family are residing .
for further evaluation , fibrinogen mixing test ( table 2 ) was run and the results showed no significant improvements in the fibrinogen level .
the plasma fibrinogen activities of the patient 's parents by clauss method were within normal range ( 309 and 254 mg / dl , respectively ) .
molecular genetic study was performed only with his parents , including his father who had a history of easy bruising , and they both were homozygous for the wild - type allele ( fig .
dysfibrinogenemia was suggested in the subject according to the initial plasma fibrinogen activity and antigen levels .
the patient himself decided not to take operation after the diagnosis of dysfibrinogenemia , although cryoprecipitate treatment was possible .
cryoprecipitate contains factor viii , fibrinogen , von willebrand factor and factor xiii , so it is generally used for dysfibrinogenemia .
although he was born with bleeding tendency , the patient had no symptoms of bleeding or thrombosis after childhood . according to cote et al.(1 ) ,
an examination of the clinical symptoms associated with -dysfibrinogenemia shows that < 5% of the individuals experienced significant bleeding , and < 30% showed thrombotic tendencies .
unfortunately , data on long - term follow - up of dysfibrinogenemic patients are rarely available .
 met310thr was already reported by the names of asahi ( 6 ) , frankfurt vii ( 7 ) , and hannover xxiv ( 2 ) .
details of biochemical mechanisms involved in fibrin polymerization , release of fibrinopeptides a / b , factor xiiia - mediated cross - linking profiles , and the position of glycosylation were elucidated in the study of fibrinogen asahi ( 6 ) .
asahi fibrinogen showed normal release of fibrinopeptides a / b , but fibrin polymerization and factor xiiia - mediated -chain cross - linking were severely impaired regardless of calcium ions , which was caused by n - glycosylation consensus sequence asn ( 308)-gly ( 309)-thr ( 310 ) conferred by the mutation ( 1 , 6 , 8) .
specifically , severely impaired polymerization of asahi fibrin monomers may account for extremely retarded cross - linking between the two asahi -chains , although the amine receptor  gln ( 398 ) was found to function normally ( 1 , 6 , 8) . those functional abnormalities could explain fibrinogen asahi patient 's bleeding tendency as well as that of the fibrinogen yecheon subject , which was supported by the ultrastructure of fibrinogen caracas ii ( a ser434 to n - glycosylated asn ) detected with the use of scanning electron microscopy . in the microscopic image , large pores bounded by local fiber networks made up of thin fibers were observed ( 9 ) .
normally , fibrinogen contains approximately 3% carbohydrate consisting of neuac , gal , man , and glcnac , which is linked to asn 52 on the  chain and asn 364 on the b chain ( 10 ) .
the role of glycosylation in fibrinogen function has been studied and its involvement in the clotting process was proposed ( 10 ) , although contradictory results have been reported ( 11 ) .
steric hindrance by the extra carbohydrate itself , the disruption of d : d interactions by the new glycosylation , and strong negative charges of sialic acids in the extra carbohydrate could be raised to account for disturbed fibrin polymerization or impaired cross - linking in niigata ( b asn160ser ) , asahi , and lima ( a arg141ser ) fibrins , respectively ( 1 , 12 - 14 ) .
being a heterozygote , in fibrinogen yecheon , as in fibrinogen asahi , fibrin monomer containing at least one gamma chain mutated is not likely to function on making polymerization properly .
those facts , therefore , suggested extra glycosylated gamma chain not only dysfunction on polymerization but also inhibit normal fibrin and fibrinogen resulting in hardly clotting with thrombin in fibrinogen activity assay by clauss method .
in addition , the subject 's coagulation abnormality was thought to be caused by extra glycosylation of -chain and subsequent disruption of d : d interaction because other coagulation factors were within normal ranges ( table 1 ) .
usually , dysfibrinogenemias having extra glycosylations concerned hemorrhagic tendency unlike tokyo v (  ala327-thr ) fibrinogen which was somewhat unique in that its propositus was thrombophilic partly owing to fibrinolysis - resistant fibrin clots despite the very low clottability of the fibrin .
it was suggested that tissue plasminogen activator binding to tokyo v fibrinogen might have been affected directly .
the subject of fibrinogen yecheon presented de novo mutation in fgg , while his parents did not show any coagulation abnormalities including dna sequencing .
de novo mutations are associated with advancing paternal age ( 15 ) and pollutants ( 16 , 17 ) . one thing
different between yecheon and asahi subjects was the level of fdp , which was normal ( 2.3 g / ml ) for the yecheon subject while that was markedly increased to 160 g / ml for the asahi patient .
because d - dimer level was within normal range , the yecheon subject was not considered in the state of hyperfibrinolysis , which was partially supported by the normal levels of plasminogen and antithrombin . as a follow - up
, a further study can be conducted to understand what brought about marked increase in fdp level for asahi subject .
fibrinogen yecheon is the only congenital dysfibrinogenemia in korea associated with bleeding tendency , and not thrombosis or amyloidosis .
our subject was born with bleeding tendency , although he had no history of serious bleeding symptoms . in general ,
two patients , baltimore i ( gly292val ) and giessen iv ( asp-318gly ) , who experienced mild bleeding symptoms , also suffered from thrombotic tendencies . the only -dysfibrinogenemia associated with a serious bleeding diathesis is asahi i ( met310thr ) . in this instance , the bleeding symptoms were probably related to the extra glycosylation resulting from the substitution ( 1 ) . in conclusion , this report describes a variant fibrinogen , hereinafter called " fibrinogen yecheon " , using the name after the town where the patient was living at the time of diagnosis ( 2 ) .
fibrinogen yecheon has a de novo heterozygous point mutation of fgg resulting in  met310thr and subsequent extra n - glycosylation at  asn308 .
 this case study reports a rare fibrinogen variant ,  met310thr mutation , for the first time in korea . 
 the case shows a point mutation from t to c in the 1,007th nucleotide of the fgg gene . 
 this report describes a variant fibrinogen , hereinafter called " fibrinogen yecheon " , using the name after the town where the patient was living at the time of diagnosis . 
 fibrinogen yecheon has a de novo heterozygous point mutation of fgg resulting in  met310thr and subsequent extra n - glycosylation at  asn308 . 
 extra n - glycosylated fibrinogen is considered a main inhibitor of normal fibrinogen activity . 
INTRODUCTION
CASE REPORT
DISCUSSION