title: Cobalamin C defect presenting as severe neonatal hyperammonemia.
abstract: Cobalamin C (Cbl-C) defect is the most common inborn error of cobalamin metabolism which causes a block in the pathway responsible for the synthesis of its two metabolically active forms methyl- and adenosylcobalamin. Cbl-C defect causes the accumulation of methylmalonic acid and homocysteine and decreased methionine synthesis. The clinical presentation of patients with early-onset Cbl-C defect, characterized by a multisystem disease with severe neurological, ocular, hematological, renal, gastrointestinal, cardiac, and pulmonary manifestations, differs considerably from what observed in the "classical" form of methylmalonic aciduria caused by defect of methylmalonyl-CoA mutase. This last condition is in most cases dominated in the neonatal period by a metabolic encephalopathy "intoxication type" with severe hyperammonemia and ketoacidosis. We report a Cbl-C defect patient presenting a neonatal encephalopathy with severe hyperammonemia and ketoacidosis who was successfully treated with peritoneal dialysis.
  
  
  CONCLUSIONS
  To the best of our knowledge, there are no reported cases of Cbl-C defect showing an acute presentation resembling a classical methylmalonic aciduria. This observation enlarges the spectrum of inherited diseases to be considered in the differential diagnosis of neonatal hyperammonemia.
authors.affiliation: Division of Metabolism, Bambino Gesù Children's Hospital, Rome, Italy. diego.martinelli@opbg.net
authors.forename: Diego
authors.initials: D
authors.lastname: Martinelli
authors.forename: Andrea
authors.initials: A
authors.lastname: Dotta
authors.forename: Laura
authors.initials: L
authors.lastname: Massella
authors.forename: Stefano
authors.initials: S
authors.lastname: Picca
authors.forename: Alessandra
authors.initials: A
authors.lastname: Di Pede
authors.forename: Sara
authors.initials: S
authors.lastname: Boenzi
authors.forename: Chiara
authors.initials: C
authors.lastname: Aiello
authors.forename: Carlo
authors.initials: C
authors.lastname: Dionisi-Vici
mesh_terms: D000592:Amino Acid Metabolism, Inborn Errors / Q000150:complications / Q000175:diagnosis*; D003937:Diagnosis, Differential; D005260:Female; D006712:Homocystinuria / Q000150:complications / Q000175:diagnosis*; D006801:Humans; D022124:Hyperammonemia / Q000209:etiology*; D007231:Infant, Newborn; D014806:Vitamin B 12 Deficiency / Q000151:congenital