Stable isotope dilution analysis of isovalerylglycine in amniotic fluid and urine and its application for the prenatal diagnosis of isovaleric acidemia.
A stable isotope dilution method was developed to measure accurately small amounts of isovalerylglycine in amniotic fluid and urine for the prenatal diagnosis of isovaleric acidemia. [4,4,4-D3]Isovalerylglycine was synthesized and used as an internal standard. Samples were extracted, methylated, and analyzed by chemical ionization gas chromatography-mass spectrometry operated in the selected ion monitoring mode. This method is very sensitive (lower limit approximately 5 ng/ml), linear over three orders of magnitude above 10 ng/ml up to at least 10 micrograms/ml and reproducible. No isovalerylglycine was detected at all in amniotic fluids from eleven normal pregnant women with an exception of a single case which contained 6 ng/ml. Amniotic fluids from five pregnancies at risk were analyzed. Two of these samples had isovalerylglycine concentrations of 957 and 556 ng/ml. Three others contained 18, 18, and 17 ng/ml of isovalerylglycine. Postpartum diagnostic tests and/or in vitro assay of isovaleryl-CoA dehydrogenase of [1-14C] isovaleric acid oxidation using amniocytes confirmed that the first two fetuses were affected by isovaleric acidemia, whereas the latter three were unaffected. The method described in this report provides a highly accurate and reliable technique for the prenatal diagnosis of isovaleric acidemia.
D G
DG
Hine
A M
AM
Hack
S I
SI
Goodman
K
K
Tanaka
D000592:Amino Acid Metabolism, Inborn Errors / Q000175:diagnosis*; D000653:Amniotic Fluid / Q000032:analysis*; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D005998:Glycine / Q000031:analogs & derivatives* / Q000032:analysis / Q000652:urine; D045782:Hemiterpenes; D006801:Humans; D010421:Pentanoic Acids / Q000097:blood*; D011247:Pregnancy; D011296:Prenatal Diagnosis; D012306:Risk; D014631:Valerates / Q000097:blood*
D045782:Hemiterpenes; D010421:Pentanoic Acids; D014631:Valerates; C008216:isovaleric acid; C005916:N-isovalerylglycine; D005998:Glycine