LAUSR

Background Methylmalonic Aciduria and Homocystinemia, cobalamin C (cblC) is an inherited disease of vitamin B 12 metabolism with a wide spectrum of clinical manifestations. cblC presenting with pulmonary hypertension (PH) as leading sympotom is rare and easily misdiagnosed because of limited awareness. Timely diagnosis is crucial by the relentless progression without appropriate treatment. Case presentation We reported a 12-year-old girl with a 3-year history of progressively reduced activity tolerance and a 3-month history of orthopnea. Metabolic testing revealed increased levels of plasma homocysteine and urine methylmalonic acid. cblC deficiency was subsequently confirmed by genetic testing. The patient was treated with hydroxocobalamin, betaine, folinic acid and levocarnitine for cblC disease. Sildenafil, bosentan, spironolactone and hydrochlorothiazide was administrated for PH and right heart failure. At 3-month follow-up, she had an apparent resolution of dyspnea and cyanosis. Metabolic abnormalities resolved the decrease of plasma homocysteine and urine methylmalonic acid. A right heart catheterization showed a reduced pulmonary pressure. Conclusions This case emphasizes the importance of an early diagnosis and initiation of treatment for cblC deficiency. Unexplained PH in children and young adults should prompt metabolic screening for the differential diagnosis.