Fibrinogen Chapel Hill: hypodysfibrinogenemia with a tertiary polymerization defect

Area of Science:

• Biochemistry
• Hematology
• Molecular Biology

Background:

• Fibrinogen is a crucial protein for blood clot formation.
• Defects in fibrinogen can lead to bleeding disorders or thrombosis.
• Fibrinogen Chapel Hill presents as a hypofibrinogenemia with functional deficits.

Observation:

• Investigated a patient with functionally defective fibrinogen (Chapel Hill).
• Observed hypofibrinogenemia with normal fibrinogen survival and fibrinopeptide release.
• Identified a polymerization defect leading to delayed fibrin gel formation.

Findings:

• The defect stems from an abnormality in a tertiary contact site within the alpha chain's hydrophilic, carboxy-terminal segment.
• Delayed plasmin cleavage of fibrinogen and fragment X, impacting subsequent fragment generation (Y, D, E).
• Demonstrated unusual sensitivity to Ancrod proteolysis, with rapid cleavage of the alpha chain's carboxy-terminal segment.

Implications:

• Structural abnormality in the alpha chain's polymerization domain explains observed functional deficits.
• Provides insights into fibrinogen structure-function relationships and clot polymerization mechanisms.
• Understanding such defects is vital for diagnosing and managing rare bleeding disorders.