Haemolytic uraemic syndrome and pulmonary hypertension in a patient with methionine synthase deficiency

An 18-month-old girl presented with macrocytic megaloblastic anaemia follow ed by haemolytic uraemic syndrome. Metabolic investigations led to the iden tification of an inborn error of cobalamin metabolism consisting of defecti ve methylcobalamin biosynthesis, probably cobalamin G, since methionine syn thase activity was decreased under standard reducing conditions. Despite tr eatment, pulmonary hypertension progressively developed and responded to ox ygen therapy. Renal involvement evolved to terminal failure and haemodialys is, while pulmonary hypertension was controlled by oxygen therapy. Such cli nical manifestations have never been reported in association with a defect of methylcobalamin and thus of methionine biosynthesis. Conclusion A congenital abnormality of cobalamin metabolism was suspected t hen confirmed in the presence of typical haematological features associated with unusual clinical manifestations such as progressive renal failure and pulmonary hypertension.