Prenatal diagnosis of methylmalonic acidemia by amniotic fluid metabolites analysis using mass spectrometry

Abstract

Objective To investigate the effect of tandem mass spectrometry and gas chromatography–mass spectrometry to make prenatal diagnosis of methylmalonic acidemia (MMA) by detecting organic acid and acylcarnitine in amniotic fluid. Methods From October 11, 2007 to December 20, 2014, 131 pregnant women with MMA proband received prenatal diagnosis of MMA in Xin Hua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine (case group). Another 120 cases of pregnant women for conventional prenatal diagnosis at the same period were as control group. The pregnant women of two groups had the amniocentesis at 16 to 20 weeks of gestation. The levels of propionylcarnitine(C3) and acetylcarnitine(C2) in amniotic fluid were detected by tandem mass spectrometry. The methylmalonic acid and methylcitrate acid were detected by gas chromatography–mass spectrometry. MMA gene of cells in amniotic fluid of eighty fetuses with proband clearly diagnosed were detected by gene testing. Data were analyzed by Wilcoxon test. Results In case group, 29 fetuses were found positive for higher level of C3, C3/C2, methylmalonic acid and methylcitrate acid compared with normal reference value, and the detected rate of fetal MMA was 22.1%(29/131). The levels of C3 and C3 / C2 in amniotic fluid of these 29 cases were higher than those in control group[8.13(2.42–16.70) vs 1.04(0.52–3.40) µmol/L, Z =–8.313; 0.77(0.30–1.79) vs 0.10(0.05–0.22), Z=–8.374; P 0.05); while they were lower than those of positive MMA fetuses (all P<0.05). Among 29 positive fetuses, 16 fetuses were detected MMA gene, five were diagnosed as MUT forms of MMA and 11 were MMACHC forms of MMA. In 102 MMA negative fetuses, 64 fetuses were detected MMA gene, 44 were found one mutant site and 20 were found no gene mutation. The coincidence rate between gene detecting and mass spectrometry was 100%(80/80). Conclusions Mass spectrometry could be used to measure the C3, methylmalonic acid and methylcitrate acid levels in amniotic fluid of pregnant women with MMA proband to make prenatal diagnosis. Key words: Amino acid metabolism, inborn errors; Prenatal diagnosis; Amniotic fluid; Tandem mass spectrometry; Gas chromatography–mass spectrometry