Gamma371 Thr-->Ile substitution in the fibrinogen gammaD domain causes hypofibrinogenaemia.
Six members of a family with hypofibrinogenaemia had fibrinogen concentrations ranging from 0.5 to 1.1 mg/ml and, after sequencing the entire coding region and the intron exon boundaries of all three fibrinogen genes, a single heterozygous ACT-->ATT mutation was identified in the gamma gene. This novel mutation was not detected in normal family members or unrelated controls. The gamma371 Thr-->Ile substitution occurs at a conserved threonine in the gammaD domain, but molecules containing the new isoleucine were not present in circulating fibrinogen. The evidence for this was that purified gamma chains had a normal mass of 48375 Da compared to a control of 48374 Da, and tryptic peptide maps were entirely normal. The mutation predicts a mass increase of 12 Da in peptide T-36, but on mass mapping only the normal [M+2H] ion was detected, at 948 m/z. There was no new signal at 954 m/z that would indicate expression of variant chains. Also the normal 948 m/z signal was at the same intensity in digests from the proposita and controls. Crystal structures show a hydrogen bond from the threonine hydroxyl to the main chain and this case suggests this bond is critical in maintaining the structure of the gammaD domain.
Brennan
S O
SO
Molecular Pathology Laboratory, Canterbury Health Laboratories, P.O. Box 151, Christchurch, New Zealand. steve.brennan@chmeds.ac.nz
Wyatt
J M
JM
Fellowes
A P
AP
Dlott
J S
JS
Triplett
D A
DA
George
P M
PM
D000328:Adult; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D004591:Electrophoresis, Polyacrylamide Gel; D005091:Exons; D005260:Female; D005340:Fibrinogen / Q000737:chemistry / Q000235:genetics*; D015241:Fibrinogens, Abnormal / Q000737:chemistry / Q000235:genetics*; D006579:Heterozygote; D006801:Humans; D013058:Mass Spectrometry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D014357:Trypsin
D015241:Fibrinogens, Abnormal; D005340:Fibrinogen; D014357:Trypsin