Comparing amniotic fluid mass spectrometry assays and amniocyte gene analyses for the prenatal diagnosis of methylmalonic aciduria

Abstract

Background Methylmalonic aciduria (MMA), a rare inherited disorder, is the most common organic aciduria in China, and prenatal diagnosis has contributed to its prevention. However, the prenatal diagnosis of MMA using cultured amniocytes or chorionic villi to detect gene mutations is exclusively applicable to families with a definite genetic diagnosis. To evaluate the reliability of mass spectrometry assays for the prenatal diagnosis of MMA, we conducted a retrospective study of our 10 years’ experience. Materials and methods This retrospective compare study reviewed the medical records for maternal and fetuses data for 287 mothers with a family history of MMA from June 2010 to December 2020. Methylmalonate and propionylcarnitine in cell-free amniotic fluid were measured using a stable isotope dilution method (GC/MS) and MS/MS-based method (LC/MS/MS). Total homocysteine (tHcy) was measured by fluorescence polarization immunoassay. Depending on the presence of disease-causing gene mutations in probands, gene studies on amniocytes from 222 pregnant women were performed. Results For 222 fetuses of the families with definite genetic diagnosis, gene analyses were performed using cultured amniocytes. 52 fetuses were affected by MMA, whereas 170 were “unaffected”. For GC/MS and LC/MS/MS, the specificity was 96.5% and 95.9%, sensitivity was 71.2% and 84.6%, respectively. The positive and negative predictive values were 86.0% and 91.6% and 86.3% and 95.3%, respectively. Propionylcarnitine/butyrylcarnitine ratio showed the highest accuracy and could thus serve as a sensitive indicator to identify those at a risk for MMA. When GC/MS and LC/MS/MS were performed in parallel, the specificity was 92.5% and sensitivity was 95.6%. When evaluating tHcy, the positive and negative predictive values were 95.0% and 96.1%, respectively. In 65 fetuses without family genetic diagnosis, 11 were finally confirmed to have MMA and 54 were “unaffected” by amniotic fluid biochemical assays. The 54 children showed normal urine organic acids and healthy development after birth. Conclusions Amniotic fluid biochemical assays using GC/MS and LC/MS/MS in parallel increased the accuracy of prenatal diagnosis of MMA. Propionylcarnitine is a more reliable marker than methylmalonic acid in amniotic fluid. Further, tHcy is recommended for the prenatal diagnosis of combined MMA and homocysteinemia.

Case report: An asymptomatic mother with an inborn error of cobalamin metabolism (cblC) detected through high homocysteine levels during prenatal diagnosis

“…The families of these patients bear significant financial and psychological burdens. Nevertheless, it is evident that biochemical techniques also have their shortcomings (8).…”

“…The c.658_660delAAG was one of the most common mutations in China (26). It seems that a rapid and precise technique for the prenatal diagnosis of methylmalonic acidemia is the biochemical analysis of amniotic fluid samples using GC-MS and/or LC-MS/MS combined with the total homocysteine assay; nevertheless, it is extremely recommended to incorporate the gene assessment during parental diagnosis (8).…”

“…Reports from the literature have shown that during prenatal diagnosis of methylmalonic acidemia, prompt reliable results could be provided utilizing biochemical analysis of amniotic fluid (7)(8)(9). The challenge posed by the absence of genetic assessment for families prone to cblC defect fetuses could be resolved by applying these techniques (8,10). Thus, this study reports the case of an asymptomatic pregnant mother who suffered from a congenital anomaly of cobalamin metabolism (cblC type) during prenatal diagnosis.…”

“…Therefore, crucial information could be provided through prenatal diagnosis concerning a decision about pregnancy that involves a fetus suffering from cblC defect that tends to subsequently minimize the social and family pressure brought by this defect (3). Reports from the literature have shown that during prenatal diagnosis of methylmalonic acidemia, prompt reliable results could be provided utilizing biochemical analysis of amniotic fluid (7)(8)(9). The challenge posed by the absence of genetic assessment for families prone to cblC defect fetuses could be resolved by applying these techniques (8,10).…”