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Given an abstract of a paper, generate a title for this paper such that conveys the key focus of the paper.

Abstract: Protein S deficiency is inherited as an autosomal dominant trait. Heterozygotes with a reduction of 50% in the plasma protein S concentration are at risk for the development of venous thromboembolism, often occurring at an early age without an apparent cause. In the majority of the patients thrombosis is restricted to the superficial or deep venous system of the legs. In this case report we describe the presence of mesenteric vein thrombosis in a 30-yr-old man with hereditary protein S deficiency. In his family protein S deficiency was also recognized in his mother, brother, and niece. Both his mother and brother had a history of thrombotic disease.
Output:
Mesenteric vein thrombosis as presenting manifestation of hereditary protein S deficiency.