Clotting factors: Clinical biochemistry and their roles as plasma enzymes

The purpose of this review is to describe structure and function of the multiple proteins of the coagulation system and their subcomponent domains. Coagulation is the process by which flowing liquid blood plasma is converted to a soft, viscous gel entrapping the cellular components of blood including red cells and platelets and thereby preventing extravasation of blood. This process is triggered by the minimal proteolysis of plasma fibrinogen. This transforms the latter to sticky fibrin monomers which polymerize into a network. The proteolysis of fibrinogen is a function of the trypsin-like enzyme termed thrombin. Thrombin in turn is activated by a cascade of trypsin-like enzymes that we term coagulation factors. In this review we examine the mechanics of the coagulation cascade with a view to the structure-function relationships of the proteins. We also note that two of the factors have no trypsin like protease domain but are essential cofactors or catalysts for the proteases. This review does not discuss the major role of platelets except to highlight their membrane function with respect to the factors. Coagulation testing is a major part of routine diagnostic clinical pathology. Testing is performed on specimens from individuals either with bleeding or with thrombotic disorders and those on anticoagulant medications. We examine the basic in-vitro laboratory coagulation tests and review the literature comparing the in vitro and in vivo processes. In vitro clinical testing typically utilizes plasma specimens and non-physiological or supraphysiological activators. Because the review focuses on coagulation factor structure, a brief overview of the evolutionary origins of the coagulation system is included.

NK cell enteropathy: a case report with 10 years of indolent clinical behaviour

AIMS

Natural killer (NK) cell enteropathy is a recently described clinically indolent condition characterised by atypical NK cell infiltrates in the gastrointestinal mucosa that mimics malignant lymphoma. We report a case that highlights the indolent clinical behaviour by documenting absence of clinical progression over 10 years.

METHODS AND RESULTS

We report the case of a 69-year old female who had clinically long-standing abdominal pain and recurrent mucosal ulcerations associated with atypical NK cell infiltrates. The clinical, morphologic and immunophenotypical findings in this case were diagnostic of NK cell enteropathy. Review of the patient's prior biopsies demonstrated that this persisted without clinical progression for 10 years, confirming the clinical indolent course.

CONCLUSION

Recognition of NK cell enteropathy is important to avoid over-diagnosing this benign condition as an aggressive lymphoma.