Newborn Screening for Hepatorenal Tyrosinemia: Tandem Mass Spectrometric Quantification of Succinylacetone

Abstract

Background: False-positive and false-negative results occur in current newborn-screening programs for hepatorenal tyrosinemia, which measure tyrosine concentrations in blood spots, sometimes in combination with other metabolites, including succinylacetone. We present our experience with a newly described method for succinylacetone quantification in routine newborn screening. Methods: Succinylacetone was extracted from blood spots that had already been extracted with absolute methanol for acylcarnitine and amino acid analysis. The solvent was acetonitrile-water (80:20 by volume) containing formic acid, hydrazine hydrate, and 100 nmol/L 5,7-dioxooctanoic acid as internal standard. Analysis was performed by tandem mass spectrometry in a separate run. Results: Of 61 344 samples, 99.6% had succinylacetone concentrations <5 mol/L. With a cutoff of 10 mol/L, no false-positive results were obtained. In 2 patients, the succinylacetone concentrations in the dried blood spots from the 36th and 56th hours of life were 152 and 271 mol/L, respectively, and the tyrosine concentrations were 54 and 129 mol/L. Hepatorenal tyrosinemia was subsequently confirmed in both patients. Retrospective analysis of the neonatal screening samples of 2 addi-

Performance of succinylacetone assays and their associated proficiency testing outcomes

“…Hepatorenal tyrosinemia newborn screening (NBS) tests based on tyrosine elevation lack specificity because neonatal hypertyrosinemia also occurs in other physiological and pathological conditions and lack sensitivity because tyrosine levels are not consistently elevated in affected newborns [2][3][4]. Succinylacetone (SUAC) is accumulated in the blood of newborns with hepatorenal tyrosinemia and is specific for that disorder [5].…”

“…Succinylacetone (SUAC) is accumulated in the blood of newborns with hepatorenal tyrosinemia and is specific for that disorder [5]. The development of tandem mass spectrometry (MS/MS) NBS methods for measuring SUAC concentration [2,4,6] has produced higher specificity of measurements, resulted in reduced risk of falsepositive and false-negative reports, and achieved better acceptance of hepatorenal tyrosinemia in NBS panels.…”

Combined Newborn Screening for Succinylacetone, Amino Acids, and Acylcarnitines in Dried Blood Spots

“…The extract is then analyzed by MS/MS. This method requires dedicated MS/MS equipment, which hinders adoption of this method into routine screening (6 ). Several other programs, for example in Minnesota, have implemented a second-tier approach where SUAC is determined only when the concentration of tyrosine in the primary screening is above a conservatively chosen cutoff value (7,8 ).…”

Application of a Second-Tier Newborn Screening Assay for C5 Isoforms

“…By using a recently established second-tier test based on the tandem-MS technique (Janzen et al 2013), we could identify pivalic acid in a dried blood sample taken during routine neonatal screening. Second-tier tests are not uncommon in newborn screening to identify false-positive results, for example in tyrosinemia type I (Sander et al 2006). …”