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

Abstract

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. 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. Of 61,344 samples, 99.6% had succinylacetone concentrations < or =5 micromol/L. With a cutoff of 10 micromol/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 micromol/L, respectively, and the tyrosine concentrations were 54 and 129 micromol/L. Hepatorenal tyrosinemia was subsequently confirmed in both patients. Retrospective analysis of the neonatal screening samples of 2 additional known patients revealed increased succinylacetone concentrations of 46 and 169 micromol/L, respectively. Tandem mass spectrometric quantification directly from residual blood spots is a useful method for the early detection of hepatorenal tyrosinemia in newborn-screening programs.