Neonatal screening for galactosemia by quantitative analysis of hexose monophosphates using tandem mass spectrometry: A retrospective study

Background: Classic galactosemia (OMIM 230400) is an inherited disorder in the metabolism of galactose caused by deficiency of the enzyme galactose 1- phosphate uridyl transferase (EC 2.7.7.12). Galactosemia leads to accumulat ion of galactose and galactose 1-phosphate (gal-1-P) in blood and tissues a nd, if untreated, produces neonatal death or severe mental retardation, cir rhosis of the liver, and cataracts. Hence, the disorder is included in many neonatal screening programs. Methods: We retrospectively analyzed filter-paper blood samples obtained 4- 8 days postpartum for routine neonatal screening from 12 galactosemia patie nts and 2055 random controls. Total hexose monophosphates (HMPs) were used as a marker of gal-1-P and were assayed by negative-ion mode electrospray t andem mass spectrometry (tandem MS) with settings biased toward gal-1-P det ection. The predominant precursor/ product ion pair m/z 259/79 was used to quantify total HMPs by external standardization. Results: Linear calibration curves were obtained in the range 0-8 mmol/L ga l-1-P. The detection limit was 0.1 mmol/L HMP, and total CVs ranged from 13 % at the detection limit to <8% at >1 mmol/L HMP. The method was in agreeme nt with an alkaline phosphatase-galactose dehydrogenase method. All samples from galactosemia patients contained increased HMP concentrations (range f or patients, 2.6-5.2 mmol/L; range for reference group, <0.10-0.94 mmol/L). The diagnostic sensitivity and specificity were 100% at a cutoff of 1.2 mm ol/L HMP. A Duarte/classic galactosemia compound heterozygous sample could be discriminated clearly from both patient and reference samples. Conclusion: Quantitative analysis of HMPs by tandem MS can be used in labor atory investigations of galactosemia. (C) 2001 American Association for Cli nical Chemistry.