The protein C pathway’s key enzyme, activated protein C, provides physiologic antithrombotic activity and exhibits both anti-inflammatory and anti-apoptotic activities. It also plays a role in the development of thrombosis and ischemic stroke.

Role in disease

Protein C deficiency is a rare genetic disorder that predisposes to venous thrombosis and habitual abortion. If homozygous, this presents with a form of disseminated intravascular coagulation in newborns termed purpura fulminans; it is treated by replacing the defective protein C.

Activated protein C resistance is the inability of protein C to cleave factors V and/or VIII. This may be hereditary or acquired. The best known and most common hereditary form is Factor V Leiden. Acquired forms occur in the presence of elevated Factor VIII concentrations.

Warfarin necrosis is acquired protein C deficiency due to treatment with the vitamin K inhibitor anticoagulant warfarin. In initial stages of action, inhibition of protein C may be stronger than inhibition of the vitamin K-dependent coagulation factors (II, VII, IX and X), leading to paradoxical activation of coagulation and necrosis of skin areas.

HDL and the effects of activated protein C (APC) on cells is very important.

Pharmacology

Drotrecogin alpha(activated) is recombinant activated protein C from Eli Lilly Co, USA. It is used in the treatment of severe sepsis, septic shock and disseminated intravascular coagulation. Its use has been very controversial since the results of clinical studies have been markedly varied. A new clinical trial of activated protein C for severe sepsis is currently underway.
 

This syndrome should not be confused with Miller syndrome – an unrelated rare genetic disorder – or Miller-Fisher sydrome – a form of Guillain-Barré syndrome.

Presentation

The brain is smooth (also known as lissencephaly), has an absence of sulci and gyri, has a cerebral cortex 4 layers thick instead of 6 and shows microcephaly. There is a characteristic facial appearance, delayed growth and mental development, and multiple abnormalities of the brain, heart, kidney and gastrointestinal tract.

Failure to thrive, feeding difficulties, seizures and decreased spontaneous activity are often seen, and death tends to occur in infancy and childhood.

Genetics

Originally thought to be an autosomal recessive disorder, it is now known to be an autosomal dominant disorder, and a haploinsufficiency of one or more genes on chromosome 17p.

The disease arises from the deletion of part of 17p (which includes both the LIS1 and 14-3-3 epsilon gene), leading to partial monosomy. There may be unbalanced translocations (ie 17q:17p or 12q:17p), or the presence of a ring chromosome 17.

Diagnosis

The disease may be diagnosed by cytogenetic techniques, testing for a microdeletion at LIS1.