Laboratory evaluation revealed a heterozygous A1298C mutation of MTHFR (GenBank U09806) and a serum homocysteine level at the upper limit of normal, 1.26 mg/L (reference range, 0.4-1.4 mg/L). Analysis of MTHFR mutation was performed as part of a thorough investigation to exclude any underlying cause of cutaneous ulceration: PG is a diagnosis of exclusion. The patient's hemoglobin concentration was 7.9 g/dL (reference range, 13.9-17.1 g/dL) with a microcytic mean corpuscular volume of 64.9 fL (reference range, 82.1-97.7 fL) and a total iron level of 7 μg/dL (reference range, 29-105 μg/dL), consistent with iron-deficiency anemia. (To convert homocysteine to micromoles per liter, multiply by 7.397; to convert hemoglobin to grams per liter, multiply by 10; to convert iron to micromoles per liter, multiply by 0.179.) A urinalysis and assays of the following showed negative or normal results: beta-2 glycoprotein-1 antibody, antistreptolysin O titer, cytoplasmic antineutrophil cytoplasmic antibody (c-ANCA), perinuclear ANCA (p-ANCA), cryoglobulins, cryofibrinogens, cryoprecipitates, antinuclear antibodies (ANA), anticardiolipin antibodies, lupus anticoagulants, factor V Leiden mutation, antithrombin III level, prothrombin 20210A mutation, hepatitis A, B, and C, urine protein electrophoresis, serum protein electrophoresis, and rheumatoid factor. A chest radiograph was also normal. Antibodies against tissue transglutaminase, endomysium, and gliaden were not evaluated. An esophagogastroduodenoscopy revealed villous blunting consistent with celiac sprue. A colonoscopy found no evidence of inflammatory bowel disease.