title: An improved LC-MS/MS method for the detection of classic and low excretor glutaric acidemia type 1.
abstract: Glutaric acidemia type I (GA1) is associated with elevated glutarylcarnitine (C5DC), typically measured as its butylester by acylcarnitine profile analysis using tandem mass spectrometry (MS/MS) and the precursor-product ion pair of m/z 388-85. This method neither distinguishes between C5DC and its isomer 3-hydroxydecanoylcarnitine (C10-OH) nor reliably detects the low-excretor variant of GA1, leading to both false-positive and false-negative results when testing for GA1. To overcome these limitations, we developed an LC-MS/MS method that discriminates C5DC from C10-OH by the use of precursor-product ion pairs specific for butylated C5DC (m/z 388-115) and underivatized C10-OH (m/z 332-85). The C5DC method was validated over the linearity range of 0.025-20 μM with a lower limit of quantification (LOQ) of 0.025 μM. Excellent precision and accuracy were also observed. We tested plasma samples from 10 patients with confirmed GA1 (including 3 with the low-excretor variant), 21 patients with mild elevations of C5DC or C10-OH by routine acylcarnitine analysis for which GA1 ultimately was excluded, and 29 normal controls. By using the m/z 388-115 ion pair, all cases of GA1, including the low-excretor variant, were reliably distinguished from normal controls. By using the m/z 388-85 pair, patients with ambiguous elevations of C5DC or C10-OH demonstrated clearly elevated levels of C10-OH (m/z 332-85) but normal C5DC (m/z 388-115), confirming that the apparent elevation of C5DC is due to interference by C10-OH. Our method results in excellent detection of GA1, including the low-excretor variant, and also provides a means to discriminate C5DC and C10-OH in follow-up testing and routine acylcarnitine studies.
authors: Department of Pathology, Stanford University, 3375 Hillview Avenue, Palo Alto, CA 94303, USA.
authors: Tereza
authors: T
authors: Moore
authors: Anthony
authors: A
authors: Le
authors: Tina M
authors: TM
authors: Cowan
mesh_terms: D000592:Amino Acid Metabolism, Inborn Errors / Q000097:blood / Q000175:diagnosis* / Q000652:urine; D001928:Brain Diseases, Metabolic / Q000097:blood / Q000175:diagnosis* / Q000652:urine; D002331:Carnitine / Q000031:analogs & derivatives / Q000097:blood / Q000652:urine; D016022:Case-Control Studies; D002853:Chromatography, Liquid / Q000379:methods*; D005500:Follow-Up Studies; D050770:Glutaryl-CoA Dehydrogenase / Q000097:blood / Q000172:deficiency / Q000652:urine; D006801:Humans; D007477:Ions; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D007477:Ions; C116917:acylcarnitine; C053168:glutarylcarnitine; D050770:Glutaryl-CoA Dehydrogenase; D002331:Carnitine