Warfarin-Associated Calciphylaxis in a Patient without Renal Failure or Hyperparathyroidism: Investigation of the Matrix GLA Protein.
Authors: Redman Rebecca , Misita Caron P. , Stafford Darrell W. , Sane David , Moll Stephan 
Published: April 2020

Abstract
Background: The etiology of calciphylaxis is unknown. Case reports have suggested an association with warfarin therapy in some patients. Matrix Gla protein (MGP) is a crucial inhibitor of vessel calcification, requiring vitamin K dependent γ-carboxylation for full function. Vitamin K antagonists inhibit MGP carboxylation. In a patient who developed calciphylaxis on warfarin we sought to determine whether an underlying defect in the MGP gene was present, such that treatment with warfarin precipitated even lower levels of MGP, leaving the patient more susceptible to calcification.
Case report: A 61 year old woman with normal renal function, calcium, phosphorus, and hyperparathyroid hormone levels developed painful, subcutaneous nodules in thighs, buttocks, and abdominal wall 14 months into warfarin therapy. Lesions became confluent and overlying skin ulcerated. Deep surgical biopsy showed extensive vascular wall calcification and fat necrosis; no inflammation was present. Thrombosis of some of the highly narrowed residual lumina was seen. Clinical presentation and pathology findings were consistent with calciphylaxis. Extensive thrombophilia work-up was negative. Warfarin was discontinued, and low-molecular weight heparin, aspirin, bisphosphonates, oral vitamin K, and antibiotics given. Within 3 months, the lesions began to heal. Additional imaging studies showed extensive calcification of medium-sized arteries, i.e. interdigital, coronary and epigastric arteries, as well as heart valves. The patient is alive 4 years after the onset of calciphylaxis, now with almost completely healed skin wounds, but with necrosis of several fingertips.
Methods and Results: Sequencing of the patient’s MGP cDNA revealed only a well-known and common polymorphism, leading to an alanine to threonine replacement in amino acid position 83, pathophysiologically likely not relevant for the calcification problem. The MGP γ-carboxylation sites were intact. Determination of plasma levels of MGP and sequencing of the non-coding region of the MGP gene are pending. A list of other candidate proteins involved in vessel wall homeostasis to be examined for genetic variants and plasma levels has been assembled and work-up for mutations and protein plasma level abnormalities started: fetuin, osteoprotegerin, bone morphogenetic protein (BMP)-2, BMP-4, osteocalcin, osteopontin, bone morphogenetic protein receptor II (BMPR2), and Runx2.
Discussion: It is known that animals treated with very large doses of warfarin develop severe vessel wall calcification due to depletion of carboxylated MGP. Other defects involving proteins of vessel wall calcium homeostasis, such as fetuin, osteoprotegerin, bone morphogenetic protein, etc., have also been shown to lead to such calcification. We postulate that calciphylaxis in our patient on warfarin developed due to a two-hit mechanism: decrease of MGP γ-carboxylation due to warfarin in an individual with a preexisting defect in vessel wall calcium homeostasis. A pathophysiologically relevant gene defect in the MGP protein has been excluded. Other candidate gene and protein abnormalities are currently being investigated.