Prenatal Diagnosis of Methylmalonic Aciduria

The abnormal accumulation of small molecular weight metabolites in amniotic fluid in inborn errors of metabolism is unusual and prenatal diagnosis usually requires amniotic cell culture and specific enzyme assay. However, Morrow et al.1 reported raised concentrations of methylmalonic acid in the amniotic fluid of a pregnancy at risk from methylmalonic aciduria and confirmed the diagnosis in the postnatal period. More recently Mahoney et al.2 have reported an abnormal methylmalonic acid concentration in the amniotic fluid of one of two pregnancies at risk. They confirmed that the fetus in this case was affected by showing an impaired oxidation of methylmalonic acid in cultured amniotic cells.