Quantitative Succinylacetone Measurement by Gas Chromatography-Tandem Mass Spectrometry (GC-MS/MS) Facilitates Diagnosis, Monitoring, and Characterization of Tyrosinemia Type 1 and Other Hypersuccinylacetonemias.

Tyrosinemia type 1 (HT1), due to deficient activity of fumarylacetoacetate hydrolase, causes accumulation of succinylacetone (SA). SA concentrations in urine and plasma of untreated HT1 patients are typically several thousand-fold higher than normal, hence are readily recognized by traditional diagnostic methods in most cases. However, quantitation of SA in the nanomolar range is important for monitoring patients treated with nitisinone, for identifying attenuated or atypical forms of HT1, and for confirmation or refutation of the diagnosis of HT1 following a positive newborn screen. Our laboratory, a reference centre for diagnosis and monitoring of HT1, previously assayed SA by gas chromatography-mass spectrometry (GC-MS). Three years ago, we upgraded this method by transferring it to a new triple quadrupole technology (GC-MS/MS). A stable isotope dilution process is used, with sample treatment consisting of an oximation step followed by a single liquid-liquid extraction then trimethylsilyl derivatization. Quantitation is based on intensities of the ion transitions m/z 620 → 181 for SA and 625 → 186 for the internal standard. Method validation demonstrated enhanced analytical specificity and sensitivity, with good precision and accuracy. Using GC-MS/MS instead of GC-MS allowed a limit of quantitation of 1 nmol/L while decreasing the required specimen volumes, as well as reducing the number of sample processing steps, chromatographic run time, and instrument maintenance. This assay facilitates laboratory diagnosis and monitoring of HT1, permits identification and characterization of other hypersuccinylacetonemias including maleylacetoacetate isomerase deficiency, and is also a valuable tool for research studies using animal models and cellular models of HT1.