Reliability of biochemical parameters used in prenatal diagnosis of combined methylmalonic aciduria and homocystinuria

Prenatal diagnosis for combined methylmalonic aciduria and homocystinuria was performed in five at-risk pregnancies by determination of methylmalonic acid (MMA) and total homocysteine (Hcy) in amniotic fluid supernatant. The incorporation rate of [ 14 C] propionate (± OHCbl) and the synthesis of cobalamin derivatives in cultured amniocytes were investigated as well as the [ 14 C] MTHF incorporation rate in intact chorion biopsy. Our experience showed that total Hcy and MMA were clearly elevated in amniotic fluid of affected fetuses. Both the study of[ 14 C] propionate incorporation and that of cobalamin synthesis in cultured amniocytes are useful to confirm the results of metabolite determination. The incorporation of [ 14 C] MTHF in intact chorion biopsy seems not to be a reliable diagnostic method.