Prenatal diagnosis of methylmalonic aciduria.

Prenatal diagnosis using amniocentesis was sought in two midtrimester pregnancies, each at risk for a different type of inherited methylmalonic aciduria. In one pregnancy a normal fetus was diagnosed from studies of cultured amniotic fluid cells and the diagnosis confirmed after the baby was born. In the second pregnancy a fetus with a methylmalonyl-CoA mutase apo enzyme defect was found. The diagnosis was based on cultured cell studies and supported by an elevation of methylmalonate in both amniotic fluid and maternal urine. Confirmatory studies were obtained using cultured cells from the aborted fetus. At the present time, assays of cultured amniotic fluid cells are imperative for firm diagnosis. With more experience, quantities of amniotic fluid and maternal urine methylmalonate may prove sufficient if differentiation among the various types of methylmalonic aciduria is not required.